Fix DesktopGrass.Native.Tests source/include paths for the module layout

The test project references the app's sources and headers; upstream they sit at
../../src/DesktopGrass.Native (tests/ vs src/ layout). In the PowerToys module the
app and tests are siblings under src/modules/DesktopGrass/, so the references are
now ../DesktopGrass.Native. Verified: builds in-tree and passes all 305 Catch2 cases.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

.github/actions/spell-check/allow/code.txt

@@ -51,6 +51,7 @@ resw
 resx
 srt
 Stereolithography
+taskmgr
 terabyte
 UYVY
 xbf
@@ -336,6 +337,10 @@ MRUCMPPROC
 MRUINFO
 REGSTR
 
+#Xaml
+NVI
+Storyboards
+
 # Misc Win32 APIs and PInvokes
 DEFAULTTONEAREST
 INVOKEIDLIST
@@ -360,7 +365,10 @@ FILESYSONLY
 URLIS
 WAITTIMEOUT
 DEFAULTTONEAREST
-
+DWRITE
+LWIN
+VCENTER
+VREDRAW
 
 # COM/WinRT interface prefixes and type fragments
 BAlt

.github/actions/spell-check/excludes.txt

@@ -105,7 +105,9 @@
 ^src/common/ManagedCommon/ColorFormatHelper\.cs$
 ^src/common/notifications/BackgroundActivatorDLL/cpp\.hint$
 ^src/common/sysinternals/Eula/
-^doc/devdocs/modules/cmdpal/initial-sdk-spec/list-elements-mock-002\.pdn$
+^src/modules/cmdpal/Tests/Microsoft\.CommandPalette\.Extensions\.Toolkit\.UnitTests/FuzzyMatcherComparisonTests.cs$
+^src/modules/cmdpal/Tests/Microsoft\.CommandPalette\.Extensions\.Toolkit\.UnitTests/FuzzyMatcherDiacriticsTests.cs$
+^src/modules/cmdpal/doc/initial-sdk-spec/list-elements-mock-002\.pdn$
 ^src/modules/cmdpal/ext/SamplePagesExtension/Pages/SampleMarkdownImagesPage\.cs$
 ^src/modules/cmdpal/Microsoft\.CmdPal\.UI/Settings/InternalPage\.SampleData\.cs$
 ^src/modules/cmdpal/Tests/Microsoft\.CmdPal\.Common\.UnitTests/.*\.TestData\.cs$

.github/actions/spell-check/expect.txt

@@ -25,6 +25,7 @@ advapi
 advfirewall
 AFeature
 affordances
+afterfx
 AFX
 agentskills
 AGGREGATABLE
@@ -62,6 +63,7 @@ APPEXECLINK
 appext
 apphost
 APPLICATIONFRAMEHOST
+Applocal
 appmanifest
 APPMODEL
 APPNAME
@@ -80,6 +82,7 @@ ARPPRODUCTICON
 ARRAYSIZE
 ARROWKEYS
 arrowshape
+artboard
 ARTIFACTSTAGINGDIRECTORY
 asf
 Ashcraft
@@ -117,7 +120,6 @@ Badmode
 Badparam
 bbwe
 BCIE
-bck
 BESTEFFORT
 bezelled
 bhid
@@ -156,6 +158,7 @@ breadcrumb
 Browsable
 BROWSEINFO
 bsd
+BSOD
 bthprops
 bti
 BTNFACE
@@ -163,6 +166,7 @@ bugreport
 bugreportfile
 BUILDARCH
 BUILDNUMBER
+buildsystems
 buildtransitive
 builttoroam
 BUNDLEINFO
@@ -200,6 +204,7 @@ checkmarks
 CHILDACTIVATE
 CHILDWINDOW
 CHOOSEFONT
+chu
 CIBUILD
 cidl
 CIELCh
@@ -222,6 +227,7 @@ CLIPSIBLINGS
 closesocket
 clp
 CLSCTX
+CLSIDs
 clsids
 Clusion
 cmder
@@ -332,6 +338,7 @@ dacl
 DAffine
 DAFFINETRANSFORM
 datareader
+Datasheet
 datatracker
 Dayof
 dbcc
@@ -368,6 +375,7 @@ DEFPUSHBUTTON
 deinitialization
 DELA
 DELD
+deld
 DELETEDKEYIMAGE
 DELETESCANS
 DEMOTYPE
@@ -392,6 +400,7 @@ DEVMODE
 DEVMODEW
 DEVNODES
 devpal
+devpackages
 DEVTYP
 dfx
 DIALOGEX
@@ -435,9 +444,9 @@ drawingcolor
 dreamsofameaningfullife
 drivedetectionwarning
 DROPFILES
+DSPDLOG
 DSTINVERT
 DString
-DSVG
 dto
 DUMMYUNIONNAME
 dumpbin
@@ -501,7 +510,6 @@ ETDT
 etl
 etw
 eula
-eurochange
 eventvwr
 evt
 EWXFORCE
@@ -542,6 +550,7 @@ FFFF
 fffffffzzz
 FFh
 Figma
+figma
 FILEEXPLORER
 fileexploreraddons
 fileexplorerpreview
@@ -631,9 +640,11 @@ gpu
 grabandmove
 GRABANDMOVEMODULEINTERFACE
 gradians
+GRC
 grctlext
 GRGX
 Gridcustomlayout
+gridlines
 GSM
 gtm
 guiddata
@@ -720,6 +731,7 @@ hotkeys
 hotlight
 hotspot
 HPAINTBUFFER
+HPS
 HRAWINPUT
 HREDRAW
 hres
@@ -783,6 +795,7 @@ imgflip
 inapp
 inbox
 INCONTACT
+indesign
 Indo
 inetcpl
 Infobar
@@ -793,6 +806,7 @@ INITDIALOG
 INITGUID
 initialfile
 INITTOLOGFONTSTRUCT
+inkscape
 INLINEPREFIX
 inlines
 Inno
@@ -836,6 +850,7 @@ issecret
 ISSEPARATOR
 issuecomment
 istep
+Italicise
 ith
 IUI
 IUWP
@@ -843,6 +858,7 @@ IWIC
 jeli
 jfif
 jgeosdfsdsgmkedfgdfgdfgbkmhcgcflmi
+JIDEA
 jjw
 jobject
 JOBOBJECT
@@ -854,6 +870,7 @@ Jsons
 jsonval
 jxr
 Kantai
+KBSC
 keybd
 KEYBDDATA
 KEYBDINPUT
@@ -871,6 +888,7 @@ keynum
 keyremaps
 keyring
 keyvault
+kfull
 KILLFOCUS
 killrunner
 kmph
@@ -974,6 +992,7 @@ lstrcmpi
 lstrcpyn
 lstrlen
 LTEXT
+LTM
 LTRREADING
 luid
 lusrmgr
@@ -1029,6 +1048,7 @@ Mgmt
 Microwaved
 middleclickaction
 midl
+midtones
 mii
 MIIM
 mikeclayton
@@ -1042,7 +1062,7 @@ MINMAXINFO
 minwindef
 Mip
 Miracast
-MIRACAST
+miracast
 mkdn
 mlcfg
 mmc
@@ -1073,6 +1093,7 @@ MOVESIZEEND
 MOVESIZESTART
 MRM
 mru
+msaccess
 MSAL
 msc
 mscorlib
@@ -1081,8 +1102,6 @@ msdata
 msdia
 MSDL
 MSGFLT
-MSHCTX
-MSHLFLAGS
 msiexec
 MSIFASTINSTALL
 MSIHANDLE
@@ -1092,13 +1111,16 @@ msixbundle
 MSIXCA
 MSLLHOOKSTRUCT
 Mso
+mspub
 msrc
 msstore
 mstsc
 msvcp
 mswhql
+MT
 MTND
 multimonitor
+Multiplayer
 MULTIPLEUSE
 multizone
 muxc
@@ -1141,7 +1163,6 @@ netcpl
 netframework
 netsetup
 netsh
-newcolor
 NEWDIALOGSTYLE
 NEWFILE
 NEWFILEHEADER
@@ -1202,6 +1223,7 @@ NORMALDISPLAY
 NORMALUSER
 NOSEARCH
 NOSENDCHANGING
+NOSIZE
 nosize
 notdefault
 NOTHOUSANDS
@@ -1242,7 +1264,6 @@ OFN
 ofs
 OICI
 OICIIO
-oldcolor
 olditem
 oldpath
 oldtheme
@@ -1309,6 +1330,7 @@ pchast
 PCIDLIST
 PCTSTR
 PCWSTR
+pdbs
 PDBs
 PDEVMODE
 PDFs
@@ -1337,6 +1359,7 @@ phbm
 phbmp
 phicon
 Photoshop
+photoshop
 phwnd
 pici
 pidl
@@ -1364,14 +1387,15 @@ POINTERID
 POINTERUPDATE
 Pokedex
 Pomodoro
-Popups
 popups
 POPUPWINDOW
+portfile
 POSITIONITEM
 POWERBROADCAST
 powerdisplay
 POWERDISPLAYMODULEINTERFACE
 powerocr
+powerpnt
 POWERRENAMECONTEXTMENU
 powerrenameinput
 POWERRENAMETEST
@@ -1427,6 +1451,7 @@ projectname
 PROPERTYKEY
 PROPVARIANT
 prot
+Prt
 PRTL
 prvpane
 psapi
@@ -1472,6 +1497,7 @@ QUERYOPEN
 QUEUESYNC
 quickaccent
 quicklinks
+quickmask
 QUNS
 RAII
 randi
@@ -1492,7 +1518,6 @@ READMODE
 READOBJECTS
 recents
 RECTDESTINATION
-rectp
 RECTSOURCE
 recursesubdirs
 recyclebin
@@ -1580,14 +1605,15 @@ SAMESHORTCUTPREVIOUSLYMAPPED
 samsung
 sancov
 SAVEFAILED
-scanled
 schedtasks
 SCID
+SCL
 Scode
 SCREENFONTS
 screenruler
 screensaver
 screenshots
+Scrollback
 scrollviewer
 sddl
 SDKDDK
@@ -1757,6 +1783,7 @@ STDAPI
 stdc
 stdcpp
 stdcpplatest
+stdext
 STDMETHODCALLTYPE
 STDMETHODIMP
 steamapps
@@ -1879,6 +1906,7 @@ TNP
 Toggleable
 tontrager
 Toolhelp
+toolsets
 toolwindow
 TOPDOWNDIB
 TOUCHEVENTF
@@ -1928,6 +1956,7 @@ ums
 uncompilable
 UNCPRIORITY
 UNDNAME
+ungroup
 UNICODETEXT
 unins
 uninsdeletekey
@@ -1940,6 +1969,8 @@ UNLEN
 UNORM
 unparsable
 unremapped
+Unsend
+Unsubscribes
 untriaged
 unvirtualized
 unwide
@@ -1974,6 +2005,7 @@ vcgtq
 VCINSTALLDIR
 vcp
 Vcpkg
+vcpkg
 vcpname
 VCRT
 vcruntime
@@ -1996,6 +2028,7 @@ VIRTKEY
 VIRTUALDESK
 VISEGRADRELAY
 visiblecolorformats
+visio
 visualeffects
 vkey
 vmovl
@@ -2080,13 +2113,16 @@ winlogon
 winmd
 winml
 WINNT
+winproj
 winres
 winrt
 winsdk
 winsta
 WINTHRESHOLD
 WINVER
+winword
 winxamlmanager
+wireframes
 withinrafael
 Withscript
 wixproj
@@ -2157,6 +2193,7 @@ xxxxxx
 ycombinator
 yinle
 yinyue
+yoko
 YVIRTUALSCREEN
 zamora
 Zenbook

.github/actions/spell-check/patterns.txt

@@ -18,6 +18,13 @@ MIcrosoftEdgeLauncherCsharp
 # marker for ignoring a comment to the end of the line
 // #no-spell-check.*$
 
+# JavaScript regex literals that start with \b can be reported as "b..." words.
+# Example: /\bclass\s+.../
+^\s*/\\[b].{3,}?/[gim]*\s*(?:\)(?:;|$)|,$)
+
+# GitHub API header token used in code (not natural language).
+\bx-ratelimit-reset\b
+
 # Gaelic
 Gàidhlig
 

.github/policies/resourceManagement.yml

@@ -163,7 +163,7 @@ configuration:
             association: Collaborator
       then:
       - addReply:
-          reply: Hi! We've identified this issue as a duplicate of another one that already exists on this Issue Tracker. This specific instance is being closed in favor of tracking the concern over on the referenced thread. Thanks for your report!
+          reply: We've identified this issue as a duplicate of an existing one and are closing this thread so discussion stays in one place.<br/><br/>Please see the comment above for the link to the original tracking issue, and feel free to subscribe there for updates.
       - closeIssue
       - removeLabel:
           label: Needs-Triage

.github/scripts/telemetry-pr-check.js

@@ -0,0 +1,377 @@
+#!/usr/bin/env node
+
+/**
+ * Detects telemetry-event additions/modifications in a pull request and
+ * posts (or updates) a PR comment when telemetry-related changes are found.
+ *
+ * This script is executed by .github/workflows/telemetry-pr-check.yml.
+ * Keep both files aligned when changing trigger behavior, env usage, or messaging.
+ */
+
+const fs = require('node:fs');
+const REVIEWER_LOGIN = 'chatasweetie';
+const REVIEWER_MENTION = `@${REVIEWER_LOGIN}`;
+
+const COMMENT_MARKER = '<!-- telemetry-event-check -->';
+const COMMENT_BODY_WITH_PRIVACY_UPDATE = `${COMMENT_MARKER}
+Thank you for contributing to PowerToys. We've detected that this PR might include a new or modified telemetry event. After this PR is merged, please follow these next steps:
+
+- [ ] Reach out to Jessica (${REVIEWER_MENTION}) to follow up on the next steps: https://aka.ms/pt-telemetry-process
+`;
+
+const COMMENT_BODY_WITHOUT_PRIVACY_UPDATE = `${COMMENT_MARKER}
+Thank you for contributing to PowerToys. We've detected that this PR might include a new or modified telemetry event. Please ensure the following before merging:
+
+- [ ] Add your telemetry events to [DATA_AND_PRIVACY](https://github.com/microsoft/PowerToys/blob/main/DATA_AND_PRIVACY.md).md within this PR.
+
+- [ ] Reach out to Jessica (${REVIEWER_MENTION}) to follow up on the next steps: https://aka.ms/pt-telemetry-process`;
+
+const TELEMETRY_PATH_PATTERNS = [
+  /(^|\/)trace\.(h|hpp|cpp|cs)$/i,
+  /(^|\/)telemetry\//i,
+  /(^|\/)events\/.+event\.cs$/i,
+  /^src\/common\/Telemetry\//i,
+  /^src\/common\/ManagedTelemetry\//i,
+  /^src\/runner\/trace\.(h|cpp)$/i,
+  /^src\/settings-ui\/.+\/Telemetry\//i,
+];
+
+const TELEMETRY_LINE_PATTERNS = [
+  /TraceLoggingWriteWrapper\s*\(/,
+  /\bTraceLoggingWrite\s*\(/,
+  /\bTRACELOGGING_DEFINE_PROVIDER\b/,
+  /\bTraceLoggingOptionProjectTelemetry\b/,
+  /\bProjectTelemetryPrivacyDataTag\b/,
+  /\bPROJECT_KEYWORD_MEASURE\b/,
+  /\bRegisterProvider\s*\(/,
+  /\bUnregisterProvider\s*\(/,
+  /\bPowerToysTelemetry\.Log\.WriteEvent\s*\(/,
+  /\bclass\s+\w+\s*:\s*EventBase\s*,\s*IEvent\b/,
+  /\bclass\s+\w+\s*:\s*TelemetryBase\b/,
+  /\bPartA_PrivTags\b/,
+  /\[EventData\]/,
+  /\bEventName\b/,
+];
+
+function requireEnv(name) {
+  const value = process.env[name];
+  if (!value) {
+    throw new Error(`Missing required environment variable: ${name}`);
+  }
+  return value;
+}
+
+function validateRepository(repository) {
+  if (!/^[^/]+\/[^/]+$/.test(repository)) {
+    throw new Error(
+      `GITHUB_REPOSITORY must be in owner/repo format, received: ${JSON.stringify(repository)}`
+    );
+  }
+}
+
+function readEventPayload(eventPath) {
+  let raw;
+  try {
+    raw = fs.readFileSync(eventPath, 'utf8');
+  } catch (error) {
+    throw new Error(`Failed to read event payload at ${eventPath}: ${error.message}`);
+  }
+
+  try {
+    return JSON.parse(raw);
+  } catch (error) {
+    throw new Error(`Failed to parse JSON from ${eventPath}: ${error.message}`);
+  }
+}
+
+function resolvePullNumber(event) {
+  const fromPullRequest = event?.pull_request?.number;
+  const fromWorkflowDispatch = event?.inputs?.pr_number;
+  const rawPullNumber = fromPullRequest ?? fromWorkflowDispatch;
+
+  if (rawPullNumber === undefined || rawPullNumber === null || rawPullNumber === '') {
+    throw new Error(
+      'Unable to determine pull request number from event payload. Expected pull_request.number or inputs.pr_number.'
+    );
+  }
+
+  const pullNumber = Number.parseInt(String(rawPullNumber), 10);
+  if (!Number.isInteger(pullNumber) || pullNumber <= 0) {
+    throw new Error(`Invalid pull request number: ${JSON.stringify(rawPullNumber)}`);
+  }
+
+  return pullNumber;
+}
+
+function isTelemetryPath(filePath) {
+  return TELEMETRY_PATH_PATTERNS.some((pattern) => pattern.test(filePath));
+}
+
+function changedLinesFromPatch(patch) {
+  if (!patch) {
+    return [];
+  }
+
+  return patch
+    .split('\n')
+    .filter((line) => {
+      if (line.startsWith('+++') || line.startsWith('---')) {
+        return false;
+      }
+      return line.startsWith('+') || line.startsWith('-');
+    })
+    .map((line) => line.slice(1));
+}
+
+function hasTelemetryLineSignal(lines) {
+  return lines.some((line) => TELEMETRY_LINE_PATTERNS.some((pattern) => pattern.test(line)));
+}
+
+async function apiRequest(url, method = 'GET', body) {
+  const token = requireEnv('GITHUB_TOKEN');
+  let response;
+  try {
+    response = await fetch(url, {
+      method,
+      headers: {
+        Authorization: `Bearer ${token}`,
+        Accept: 'application/vnd.github+json',
+        'Content-Type': 'application/json',
+      },
+      body: body ? JSON.stringify(body) : undefined,
+    });
+  } catch (error) {
+    throw new Error(`Network error during ${method} ${url}: ${error.message}`);
+  }
+
+  if (!response.ok) {
+    const text = await response.text();
+    const rateLimitReset = response.headers.get('x-ratelimit-reset');
+    const rateLimitHint =
+      response.status === 403 && rateLimitReset
+        ? ` (rate limit reset at epoch ${rateLimitReset})`
+        : '';
+    throw new Error(`${method} ${url} failed (${response.status})${rateLimitHint}: ${text}`);
+  }
+
+  if (response.status === 204) {
+    return null;
+  }
+
+  try {
+    return await response.json();
+  } catch (error) {
+    throw new Error(`Failed to parse JSON response for ${method} ${url}: ${error.message}`);
+  }
+}
+
+async function getAllPullFiles(apiBaseUrl, repository, pullNumber) {
+  const files = [];
+  let page = 1;
+
+  while (true) {
+    const url = `${apiBaseUrl}/repos/${repository}/pulls/${pullNumber}/files?per_page=100&page=${page}`;
+    const batch = await apiRequest(url);
+    if (!Array.isArray(batch)) {
+      throw new Error(`Unexpected response while listing PR files on page ${page}.`);
+    }
+
+    if (batch.length === 0) {
+      break;
+    }
+
+    files.push(...batch);
+
+    if (batch.length < 100) {
+      break;
+    }
+
+    page += 1;
+  }
+
+  return files;
+}
+
+async function getPullRequest(apiBaseUrl, repository, pullNumber) {
+  const url = `${apiBaseUrl}/repos/${repository}/pulls/${pullNumber}`;
+  const pullRequest = await apiRequest(url);
+  if (!pullRequest || typeof pullRequest !== 'object') {
+    throw new Error('Unexpected response while fetching pull request details.');
+  }
+  return pullRequest;
+}
+
+async function ensureReviewerRequested(apiBaseUrl, repository, pullNumber, pullRequest) {
+  const authorLogin = String(pullRequest?.user?.login || '').toLowerCase();
+  const targetReviewer = REVIEWER_LOGIN.toLowerCase();
+
+  if (authorLogin === targetReviewer) {
+    console.log(`Skipping reviewer request: ${REVIEWER_LOGIN} is the PR author.`);
+    return;
+  }
+
+  const requestedReviewers = Array.isArray(pullRequest?.requested_reviewers)
+    ? pullRequest.requested_reviewers
+    : [];
+  const alreadyRequested = requestedReviewers.some(
+    (reviewer) => String(reviewer?.login || '').toLowerCase() === targetReviewer
+  );
+
+  if (alreadyRequested) {
+    console.log(`Reviewer ${REVIEWER_LOGIN} is already requested.`);
+    return;
+  }
+
+  const url = `${apiBaseUrl}/repos/${repository}/pulls/${pullNumber}/requested_reviewers`;
+  try {
+    await apiRequest(url, 'POST', { reviewers: [REVIEWER_LOGIN] });
+    console.log(`Requested reviewer ${REVIEWER_LOGIN}.`);
+  } catch (error) {
+    // Reviewer request should not fail the telemetry guidance workflow.
+    console.warn(
+      `Unable to request reviewer ${REVIEWER_LOGIN}: ${error instanceof Error ? error.message : String(error)}`
+    );
+  }
+}
+
+async function findExistingTelemetryComment(apiBaseUrl, repository, pullNumber) {
+  let page = 1;
+
+  while (true) {
+    const commentsUrl = `${apiBaseUrl}/repos/${repository}/issues/${pullNumber}/comments?per_page=100&page=${page}`;
+    const comments = await apiRequest(commentsUrl);
+
+    if (!Array.isArray(comments)) {
+      throw new Error(`Unexpected response while listing issue comments on page ${page}.`);
+    }
+
+    const existing = comments.find(
+      (comment) => typeof comment.body === 'string' && comment.body.includes(COMMENT_MARKER)
+    );
+    if (existing) {
+      return existing;
+    }
+
+    if (comments.length < 100) {
+      return null;
+    }
+
+    page += 1;
+  }
+}
+
+function detectTelemetryChanges(files) {
+  const matches = [];
+
+  for (const file of files) {
+    const filename = file.filename || '';
+    const telemetryPath = isTelemetryPath(filename);
+    const changedLines = changedLinesFromPatch(file.patch);
+    const telemetryLineSignal = hasTelemetryLineSignal(changedLines);
+
+    // Some large diffs omit patch content. If the file path is telemetry-centric,
+    // treat it as a telemetry modification to avoid false negatives.
+    const patchUnavailable = !file.patch && telemetryPath;
+
+    if (telemetryPath || telemetryLineSignal || patchUnavailable) {
+      matches.push({
+        filename,
+        telemetryPath,
+        telemetryLineSignal,
+        patchUnavailable,
+      });
+    }
+  }
+
+  return matches;
+}
+
+function hasDataAndPrivacyChange(files) {
+  return files.some((file) => {
+    const filename = (file.filename || '').toLowerCase();
+    return filename === 'data_and_privacy.md';
+  });
+}
+
+async function upsertPrComment(apiBaseUrl, repository, pullNumber, body) {
+  const existing = await findExistingTelemetryComment(apiBaseUrl, repository, pullNumber);
+
+  if (existing) {
+    const updateUrl = `${apiBaseUrl}/repos/${repository}/issues/comments/${existing.id}`;
+    await apiRequest(updateUrl, 'PATCH', { body });
+    console.log(`Updated existing telemetry comment (id: ${existing.id}).`);
+    return;
+  }
+
+  const createUrl = `${apiBaseUrl}/repos/${repository}/issues/${pullNumber}/comments`;
+  await apiRequest(createUrl, 'POST', { body });
+  console.log('Created telemetry comment on PR.');
+}
+
+async function main() {
+  const eventPath = requireEnv('GITHUB_EVENT_PATH');
+  const repository = requireEnv('GITHUB_REPOSITORY');
+  const apiBaseUrl = process.env.GITHUB_API_URL || 'https://api.github.com';
+  validateRepository(repository);
+
+  let parsedApiBaseUrl;
+  try {
+    parsedApiBaseUrl = new URL(apiBaseUrl);
+  } catch {
+    throw new Error(`Invalid GITHUB_API_URL: ${JSON.stringify(apiBaseUrl)}`);
+  }
+
+  const event = readEventPayload(eventPath);
+  const pullNumber = resolvePullNumber(event);
+
+  console.log(`Event name: ${process.env.GITHUB_EVENT_NAME || 'unknown'}`);
+  console.log(`Repository: ${repository}`);
+  console.log(`PR number: ${pullNumber}`);
+
+  const files = await getAllPullFiles(parsedApiBaseUrl.origin, repository, pullNumber);
+
+  if (files.length === 0) {
+    console.log('No changed files found for PR; skipping telemetry comment update.');
+    return;
+  }
+
+  const matches = detectTelemetryChanges(files);
+  const dataAndPrivacyChanged = hasDataAndPrivacyChange(files);
+
+  console.log(`Scanned ${files.length} changed files.`);
+  console.log(`Telemetry matches found: ${matches.length}.`);
+  console.log(`DATA_AND_PRIVACY.md changed: ${dataAndPrivacyChanged}.`);
+
+  if (matches.length === 0) {
+    console.log('No telemetry-related additions/modifications detected.');
+    return;
+  }
+
+  for (const match of matches) {
+    console.log(
+      `- ${match.filename} (telemetryPath=${match.telemetryPath}, telemetryLineSignal=${match.telemetryLineSignal}, patchUnavailable=${match.patchUnavailable})`
+    );
+  }
+
+  try {
+    const pullRequest = await getPullRequest(parsedApiBaseUrl.origin, repository, pullNumber);
+    await ensureReviewerRequested(parsedApiBaseUrl.origin, repository, pullNumber, pullRequest);
+  } catch (error) {
+    console.warn(
+      'Failed to fetch PR details or request reviewer; continuing to post telemetry guidance comment.'
+    );
+    console.warn(error instanceof Error ? error.stack || error.message : error);
+  }
+
+  const commentBody = dataAndPrivacyChanged
+    ? COMMENT_BODY_WITH_PRIVACY_UPDATE
+    : COMMENT_BODY_WITHOUT_PRIVACY_UPDATE;
+
+  await upsertPrComment(apiBaseUrl, repository, pullNumber, commentBody);
+}
+
+main().catch((error) => {
+  console.error('Telemetry PR check failed.');
+  console.error(error instanceof Error ? error.stack || error.message : error);
+  process.exit(1);
+});

.github/workflows/auto-label-issues.yml

@@ -28,7 +28,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Apply area labels with AI
-        uses: actions/github-script@v9
+        uses: actions/github-script@v7
         env:
           # actions/github-script does not propagate `github-token` to
           # process.env. Expose it explicitly so the inline script can
@@ -88,8 +88,8 @@ jobs:
                 'Product-Advanced Paste',
                 'Product-Always On Top',
                 'Product-Awake',
-                'Product-ColorPicker',
-                'Product-Command Not Found',
+                'Product-Color Picker',
+                'Product-CommandNotFound',
                 'Product-Command Palette',
                 'Product-CropAndLock',
                 'Product-Environment Variables',
@@ -98,7 +98,7 @@ jobs:
                 'Product-File Locksmith',
                 'Product-Find My Mouse',
                 'Product-Grab And Move',
-                'Product-Hosts',
+                'Product-Hosts File Editor',
                 'Product-Image Resizer',
                 'Product-Keyboard Manager',
                 'Product-LightSwitch',
@@ -109,7 +109,7 @@ jobs:
                 'Product-Mouse Without Borders',
                 'Product-New+',
                 'Product-Peek',
-                'Product-Power Display',
+                'Product-PowerDisplay',
                 'Product-PowerRename',
                 'Product-PowerToys Run',
                 'Product-Quick Accent',

.github/workflows/telemetry-pr-check.yml

@@ -0,0 +1,35 @@
+# NOTE: This workflow depends on .github/scripts/telemetry-pr-check.js for telemetry detection and PR comments.
+# Keep this workflow and script behavior in sync when making changes.
+name: Telemetry PR Check
+
+on:
+  pull_request_target:
+    types: [opened, reopened, synchronize, ready_for_review]
+  workflow_dispatch:
+    inputs:
+      pr_number:
+        description: "Pull Request Number to test against"
+        required: true
+        type: string
+
+permissions:
+  contents: read
+  pull-requests: write
+
+concurrency:
+  group: telemetry-pr-check-${{ github.event.pull_request.number }}
+  cancel-in-progress: true
+
+jobs:
+  detect-telemetry-events:
+    if: ${{ github.event.pull_request.draft == false }}
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v6
+
+      - name: Detect telemetry event changes and comment PR
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+        run: node .github/scripts/telemetry-pr-check.js

.gitignore

@@ -370,3 +370,8 @@ installer/*/*.wxs.bk
 .squad-workstream
 .github/agents/**squad**.md
 .github/workflows/**squad**.yml
+
+# vcpkg manifest mode installed packages
+vcpkg_installed/
+
+deps/vcpkg/

.gitmodules

@@ -1,6 +0,0 @@
-[submodule "deps/spdlog"]
-	path = deps/spdlog
-	url = https://github.com/gabime/spdlog.git
-[submodule "deps/expected-lite"]
-	path = deps/expected-lite
-	url = https://github.com/martinmoene/expected-lite.git

.pipelines/ESRPSigning_core.json

@@ -212,6 +212,7 @@
             "WinUI3Apps\\PowerToys.NewPlus.ShellExtension.win10.dll",
 
             "PowerAccent.Core.dll",
+            "PowerAccent.Common.dll",
             "PowerToys.PowerAccent.dll",
             "PowerToys.PowerAccent.exe",
             "PowerToys.PowerAccentModuleInterface.dll",
@@ -243,8 +244,12 @@
             "WinUI3Apps\\PowerToys.RegistryPreview.dll",
             "WinUI3Apps\\PowerToys.RegistryPreview.exe",
 
-            "PowerToys.ShortcutGuide.exe",
-            "PowerToys.ShortcutGuideModuleInterface.dll",
+            "WinUI3Apps\\PowerToys.ShortcutGuide.exe",
+            "WinUI3Apps\\PowerToys.ShortcutGuide.dll",
+            "WinUI3Apps\\PowerToys.ShortcutGuideModuleInterface.dll",
+            "WinUI3Apps\\PowerToys.ShortcutGuide.IndexYmlGenerator.dll",
+            "WinUI3Apps\\PowerToys.ShortcutGuide.IndexYmlGenerator.exe",
+            "WinUI3Apps\\ShortcutGuide.CPPProject.dll",
 
             "PowerToys.ZoomIt.exe",
             "PowerToys.ZoomItModuleInterface.dll",
@@ -383,6 +388,11 @@
                 "ColorCode.Core.dll", 
                 "Microsoft.SemanticKernel.Connectors.Ollama.dll",
                 "OllamaSharp.dll",
+                "WinUI3Apps\\Google.Apis.dll",
+                "WinUI3Apps\\Google.Apis.Auth.dll",
+                "WinUI3Apps\\Google.Apis.Core.dll",
+                "WinUI3Apps\\Google.GenAI.dll",
+                "WinUI3Apps\\YamlDotNet.dll",
 
                 "boost_regex-vc143-mt-gd-x32-1_87.dll",
                 "boost_regex-vc143-mt-gd-x64-1_87.dll",

.pipelines/v2/release.yml

@@ -104,6 +104,10 @@ extends:
               # Have msbuild use the release nuget config profile
               additionalBuildOptions: /p:RestoreConfigFile="$(Build.SourcesDirectory)\.pipelines\release-nuget.config" /p:EnableCmdPalAOT=true
               beforeBuildSteps:
+                # Install the Terrapin retrieval tool, which replaces vcpkg's download handler
+                # to redirect it to a safe Microsoft-controlled location
+                - template: .pipelines/v2/templates/steps-install-terrapin.yml@self
+
                 # Sets versions for all PowerToy created DLLs
                 - pwsh: |-
                     .pipelines/versionSetting.ps1 -versionNumber '${{ parameters.versionNumber }}' -DevEnvironment ''
@@ -140,6 +144,10 @@ extends:
                 signCertName: $(SigningSignCertName)
                 useManagedIdentity: $(SigningUseManagedIdentity)
                 clientId: $(SigningOriginalClientId)
+              beforeBuildSteps:
+                # Install the Terrapin retrieval tool, which replaces vcpkg's download handler
+                # to redirect it to a safe Microsoft-controlled location
+                - template: .pipelines/v2/templates/steps-install-terrapin.yml@self
 
       - stage: Publish
         displayName: Publish

.pipelines/v2/templates/job-build-project.yml

@@ -270,6 +270,34 @@ jobs:
       parameters:
         directory: $(build.sourcesdirectory)\src\modules\cmdpal
 
+  # --- vcpkg detection + binary cache --------------------------------------
+  # PowerToys consumes spdlog (and, over time, other native deps) via vcpkg in
+  # manifest mode. steps-install-vcpkg.yml prefers the vcpkg shipped with
+  # Visual Studio (Microsoft.VisualStudio.Component.Vcpkg) and falls back to a
+  # fresh clone of microsoft/vcpkg into deps/vcpkg if VS doesn't have it.
+  # Either way it sets the VCPKG_ROOT pipeline variable; MSBuild integration
+  # is wired globally from Cpp.Build.props (with vcpkg.targets in
+  # Cpp.Build.targets) using the three-tier VcpkgRoot fallback
+  # (env var > VS-shipped > deps/vcpkg runtime clone).
+  #
+  # Vcpkg's MSBuild integration runs `vcpkg install` once per project, so the
+  # binary cache below saves ~3-5 minutes per triplet on cache hits.
+  - template: .\steps-install-vcpkg.yml
+    parameters:
+      useVSPreview: ${{ parameters.useVSPreview }}
+
+  - ${{ if eq(parameters.enablePackageCaching, true) }}:
+    - task: Cache@2
+      displayName: 'Cache vcpkg binary archives'
+      inputs:
+        # Key on the inputs vcpkg uses to compute its package ABI: the manifest,
+        # configuration, every overlay-port file, and the agent OS.
+        key: '"vcpkg" | "$(Agent.OS)" | vcpkg.json | vcpkg-configuration.json | deps/vcpkg-overlays/**'
+        restoreKeys: |
+           "vcpkg" | "$(Agent.OS)"
+           "vcpkg"
+        path: $(LOCALAPPDATA)\vcpkg\archives
+
 
 
   - ${{ parameters.beforeBuildSteps }}

.pipelines/v2/templates/job-build-sdk.yml

@@ -15,6 +15,9 @@ parameters:
   - name: signingIdentity
     type: object
     default: {}
+  - name: beforeBuildSteps
+    type: stepList
+    default: []
 
 jobs:
 - job: "BuildSDK"
@@ -45,6 +48,8 @@ jobs:
       parameters:
         directory: $(build.sourcesdirectory)\src\modules\cmdpal
 
+  - ${{ parameters.beforeBuildSteps }}
+
   - pwsh: |-
       & "$(build.sourcesdirectory)\src\modules\cmdpal\extensionsdk\nuget\BuildSDKHelper.ps1" -Configuration "Release" -BuildStep "build" -IsAzurePipelineBuild
     displayName: Build SDK

.pipelines/v2/templates/steps-install-terrapin.yml

@@ -0,0 +1,6 @@
+steps:
+- pwsh: |-
+    nuget install -source "https://microsoft.pkgs.visualstudio.com/Dart/_packaging/PowerToysDependencies/nuget/v3/index.json" TerrapinRetrievalTool -Prerelease -OutputDirectory _trt -Config "$(Build.SourcesDirectory)\.pipelines\release-nuget.config"
+    $TerrapinRetrievalToolPath = (Get-Item _trt\TerrapinRetrievalTool.*\win-x64\TerrapinRetrievalTool.exe).FullName
+    Write-Host "##vso[task.setvariable variable=X_VCPKG_ASSET_SOURCES]x-script,${TerrapinRetrievalToolPath} -b https://vcpkg.storage.devpackages.microsoft.io/artifacts/ -a true -u None -p {url} -s {sha512} -d {dst};x-block-origin"
+  displayName: Set up the Terrapin Retrieval Tool (vcpkg cache)

.pipelines/v2/templates/steps-install-vcpkg.yml

@@ -0,0 +1,41 @@
+# Adapted from microsoft/terminal build/pipelines/templates-v2/steps-install-vcpkg.yml.
+#
+# Detects vcpkg from (in order):
+#   1. The Visual Studio installation (Microsoft.VisualStudio.Component.Vcpkg,
+#      declared in the repo-root .vsconfig).
+#   2. A local clone at deps/vcpkg, cloned and bootstrapped on demand.
+#
+# Sets the pipeline-scoped VCPKG_ROOT variable; the rest of the build
+# resolves vcpkg through it (see the three-tier VcpkgRoot fallback in
+# Cpp.Build.props). No repo-level vcpkg submodule required.
+parameters:
+- name: useVSPreview
+  type: boolean
+  default: false
+
+steps:
+  - pwsh: |-
+      # vswhere -prerelease is opt-in via the useVSPreview parameter so CI on
+      # stable VS doesn't accidentally pick up a Preview install when both
+      # are present. Matches the existing useVSPreview plumbing for
+      # verifyAndSetLatestVCToolsVersion.ps1.
+      $vswhereArgs = @('-latest', '-requires', 'Microsoft.VisualStudio.Component.Vcpkg', '-property', 'installationPath')
+      $useVSPreview = '${{ parameters.useVSPreview }}' -eq 'True'
+      if ($useVSPreview) { $vswhereArgs = @('-prerelease') + $vswhereArgs }
+      $VsInstallRoot = & 'C:\Program Files (x86)\Microsoft Visual Studio\Installer\vswhere.exe' @vswhereArgs
+      If ([String]::IsNullOrEmpty($VsInstallRoot)) {
+        Remove-Item -Recurse -Force deps/vcpkg -ErrorAction:Ignore
+        git clone https://github.com/microsoft/vcpkg deps/vcpkg
+        if ($LASTEXITCODE -ne 0) { throw "git clone vcpkg failed (exit $LASTEXITCODE)" }
+        Push-Location deps/vcpkg
+        & ./bootstrap-vcpkg.bat -disableMetrics
+        if ($LASTEXITCODE -ne 0) { Pop-Location; throw "bootstrap-vcpkg failed (exit $LASTEXITCODE)" }
+        $VcpkgRoot = $PWD
+        Pop-Location
+        Write-Host "Using vcpkg from local checkout ($VcpkgRoot)"
+      } Else {
+        $VcpkgRoot = Join-Path $VsInstallRoot 'VC\vcpkg'
+        Write-Host "Using vcpkg from Visual Studio installation ($VcpkgRoot)"
+      }
+      Write-Host "##vso[task.setvariable variable=VCPKG_ROOT]$VcpkgRoot"
+    displayName: Detect VS vcpkg or bootstrap locally

.pipelines/verifyCommonProps.ps1

@@ -48,6 +48,11 @@ foreach ($csprojFile in $csprojFilesArray) {
         continue
     }
 
+    # The PowerAccent.Common project does not target WinRT, so skip it
+    if ($csprojFile -like '*PowerAccent.Common.csproj') {
+        continue
+    }
+
     $importExists = Test-ImportSharedCsWinRTProps -filePath $csprojFile
     if (!$importExists) {
         Write-Output "$csprojFile need to import 'Common.Dotnet.CsWinRT.props'."

.vsconfig

@@ -18,6 +18,7 @@
     "Microsoft.VisualStudio.Component.VC.ATL.ARM64.Spectre",
     "Microsoft.VisualStudio.Component.VC.ATL",
     "Microsoft.VisualStudio.Component.VC.ATL.Spectre",
+    "Microsoft.VisualStudio.Component.Vcpkg",
     "Microsoft.VisualStudio.ComponentGroup.WindowsAppSDK.Cs"
   ]
 }

Cpp.Build.props

@@ -39,7 +39,8 @@
   <PropertyGroup>
     <PreferredToolArchitecture>x64</PreferredToolArchitecture>
     <PreferredToolArchitecture Condition="'$(PROCESSOR_ARCHITECTURE)' == 'ARM64' or '$(PROCESSOR_ARCHITEW6432)' == 'ARM64'">arm64</PreferredToolArchitecture>
-    <VcpkgEnabled>false</VcpkgEnabled>
+    <!-- vcpkg.targets is imported via Cpp.Build.targets after Microsoft.Cpp.targets. -->
+    <ForceImportAfterCppTargets>$(MSBuildThisFileDirectory)Cpp.Build.targets</ForceImportAfterCppTargets>
     <ReplaceWildcardsInProjectItems>true</ReplaceWildcardsInProjectItems>
     <ExternalIncludePath>$(MSBuildThisFileDirectory)deps;$(MSBuildThisFileDirectory)packages;$(ExternalIncludePath)</ExternalIncludePath>
     <!-- Enable control flow guard for C++ projects that don't consume any C++ files -->
@@ -121,6 +122,48 @@
     <SpectreMitigation>Spectre</SpectreMitigation>
   </PropertyGroup>
 
+  <!--
+    vcpkg integration. Set globally and loaded before Microsoft.Cpp.props (via
+    ForceImportBeforeCppProps) so that vcpkg.props' ClCompile hook is in place
+    before the C++ targets run. VcpkgRoot is resolved via the same three-tier
+    fallback used by microsoft/terminal (env var → VS-shipped → deps/vcpkg).
+  -->
+  <PropertyGroup Label="vcpkg">
+    <VcpkgEnabled>true</VcpkgEnabled>
+    <VcpkgEnableManifest>true</VcpkgEnableManifest>
+    <VcpkgManifestEnabled>true</VcpkgManifestEnabled>
+    <VcpkgManifestRoot>$(MSBuildThisFileDirectory)</VcpkgManifestRoot>
+    <VcpkgOSTarget>windows</VcpkgOSTarget>
+    <VcpkgUseStatic>true</VcpkgUseStatic>
+    <!--
+      Force VcpkgConfiguration to follow $(Configuration). Without this,
+      vcpkg.props infers VcpkgConfiguration from $(UseDebugLibraries), which
+      Microsoft.Cpp.Default.props has already defaulted to 'false' by the
+      time vcpkg.props is imported here (the PowerToys-wide Debug override
+      below runs LATER). That would silently link the Release-built spdlog
+      into Debug consumers and trigger LNK2038 (MT/MTd, _ITERATOR_DEBUG_LEVEL).
+    -->
+    <VcpkgConfiguration>$(Configuration)</VcpkgConfiguration>
+    <!-- vcpkg validates triplets case-sensitively; PowerToys uses ARM64 capital-case. -->
+    <VcpkgPlatformTarget Condition="'$(Platform)' == 'ARM64'">arm64</VcpkgPlatformTarget>
+    <VcpkgApplocalDeps>false</VcpkgApplocalDeps>
+    <VcpkgInstalledDir>$(MSBuildThisFileDirectory)vcpkg_installed\$(Platform)\</VcpkgInstalledDir>
+    <VcpkgRoot Condition="'$(VcpkgRoot)' == ''">$(VCPKG_ROOT)</VcpkgRoot>
+    <VcpkgRoot Condition="'$(VcpkgRoot)' == '' and '$(VsInstallRoot)' != ''">$(VsInstallRoot)\VC\vcpkg</VcpkgRoot>
+    <VcpkgRoot Condition="'$(VcpkgRoot)' == '' or !Exists('$(VcpkgRoot)\vcpkg.exe')">$(MSBuildThisFileDirectory)deps\vcpkg</VcpkgRoot>
+    <CAExcludePath>$(CAExcludePath);$(VcpkgInstalledDir)</CAExcludePath>
+    <VCPkgLocalAppDataDisabled>true</VCPkgLocalAppDataDisabled>
+  </PropertyGroup>
+  <!-- Fail fast with an actionable message instead of opaque C1083 spdlog/spdlog.h errors. -->
+  <Target Name="PowerToysEnsureVcpkgAvailable"
+          BeforeTargets="PrepareForBuild"
+          Condition="'$(MSBuildProjectExtension)' == '.vcxproj' and '$(VcpkgEnabled)' == 'true' and !Exists('$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.props')">
+    <Error Text="PowerToys requires the 'vcpkg' Visual Studio component, but it was not found.%0A%0AOpen the Visual Studio Installer, click Modify on your VS install, search for 'vcpkg', enable 'C++ vcpkg package manager', and click Modify. (Visual Studio will also prompt you to install missing .vsconfig components when you open PowerToys.slnx.)%0A%0AIf you have vcpkg installed elsewhere, set the VCPKG_ROOT environment variable to its root before building.%0A%0ASearched: '$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.props'" />
+  </Target>
+  <Import Project="$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.props"
+          Condition="'$(MSBuildProjectExtension)' == '.vcxproj' and Exists('$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.props')" />
+
+
   <!-- Debug/Release props -->
   <PropertyGroup Condition="'$(Configuration)'=='Debug'" Label="Configuration">
     <UseDebugLibraries>true</UseDebugLibraries>

Cpp.Build.targets

@@ -0,0 +1,16 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project>
+  <!--
+    PowerToys global C++ post-targets. Wired in via
+    <ForceImportAfterCppTargets> in Cpp.Build.props so MSBuild loads this
+    file AFTER Microsoft.Cpp.targets for every .vcxproj.
+
+    Conditionally imports vcpkg.targets to hook ClCompile into vcpkg's
+    VcpkgInstallManifestDependencies target so spdlog headers are
+    auto-discovered on the include path and spdlog.lib is auto-linked.
+    vcpkg.props is imported in Cpp.Build.props (before Microsoft.Cpp.props);
+    vcpkg.targets needs the matching "after" hook here.
+  -->
+  <Import Project="$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.targets"
+          Condition="'$(MSBuildProjectExtension)' == '.vcxproj' and '$(VcpkgEnabled)' == 'true' and Exists('$(VcpkgRoot)\scripts\buildsystems\msbuild\vcpkg.targets')" />
+</Project>

Directory.Packages.props

@@ -41,34 +41,34 @@
     <PackageVersion Include="MessagePack" Version="3.1.3" />
     <PackageVersion Include="Microsoft.CodeAnalysis.NetAnalyzers" Version="10.0.102" />
     <PackageVersion Include="Microsoft.CommandPalette.Extensions" Version="0.9.260303001" />
-    <PackageVersion Include="Microsoft.Data.Sqlite" Version="10.0.7" />
+    <PackageVersion Include="Microsoft.Data.Sqlite" Version="10.0.8" />
     <!-- Including Microsoft.Bcl.AsyncInterfaces to force version, since it's used by Microsoft.SemanticKernel. -->
-    <PackageVersion Include="Microsoft.Bcl.AsyncInterfaces" Version="10.0.7" />
+    <PackageVersion Include="Microsoft.Bcl.AsyncInterfaces" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Graphics.Win2D" Version="1.3.2" />
     <PackageVersion Include="Microsoft.Windows.CppWinRT" Version="2.0.250303.1" />
     <PackageVersion Include="Microsoft.Diagnostics.Tracing.TraceEvent" Version="3.1.16" />
-    <PackageVersion Include="Microsoft.Extensions.AI" Version="9.9.1" />
-    <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="9.9.1-preview.1.25474.6" />
-    <PackageVersion Include="Microsoft.Extensions.Caching.Abstractions" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="10.0.7" />
-    <PackageVersion Include="Microsoft.Extensions.Hosting.WindowsServices" Version="10.0.7" />
+    <PackageVersion Include="Microsoft.Extensions.AI" Version="10.2.0" />
+    <PackageVersion Include="Microsoft.Extensions.AI.OpenAI" Version="10.0.1-preview.1.25571.5" />
+    <PackageVersion Include="Microsoft.Extensions.Caching.Abstractions" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Caching.Memory" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.DependencyInjection" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Logging" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Logging.Abstractions" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Hosting" Version="10.0.8" />
+    <PackageVersion Include="Microsoft.Extensions.Hosting.WindowsServices" Version="10.0.8" />
     <PackageVersion Include="Microsoft.AI.Foundry.Local" Version="0.3.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel" Version="1.66.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.OpenAI" Version="1.66.0" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.AzureAIInference" Version="1.66.0-beta" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.Google" Version="1.66.0-alpha" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.MistralAI" Version="1.66.0-alpha" />
-    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.Ollama" Version="1.66.0-alpha" />
+    <PackageVersion Include="Microsoft.SemanticKernel" Version="1.71.0" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.OpenAI" Version="1.71.0" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.AzureAIInference" Version="1.71.0-beta" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.Google" Version="1.71.0-alpha" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.MistralAI" Version="1.71.0-alpha" />
+    <PackageVersion Include="Microsoft.SemanticKernel.Connectors.Ollama" Version="1.71.0-alpha" />
     <PackageVersion Include="Microsoft.Toolkit.Uwp.Notifications" Version="7.1.2" />
     <PackageVersion Include="Microsoft.Web.WebView2" Version="1.0.3719.77" />
     <!-- Package Microsoft.Win32.SystemEvents added as a hack for being able to exclude the runtime assets so they don't conflict with 8.0.1. This is a dependency of System.Drawing.Common but the 8.0.1 version wasn't published to nuget. -->
-    <PackageVersion Include="Microsoft.Win32.SystemEvents" Version="10.0.7" />
+    <PackageVersion Include="Microsoft.Win32.SystemEvents" Version="10.0.8" />
     <PackageVersion Include="Microsoft.WindowsPackageManager.ComInterop" Version="1.10.340" />
-    <PackageVersion Include="Microsoft.Windows.Compatibility" Version="10.0.7" />
+    <PackageVersion Include="Microsoft.Windows.Compatibility" Version="10.0.8" />
     <PackageVersion Include="Microsoft.Windows.CsWin32" Version="0.3.269" />
     <!-- CsWinRT version needs to be set to have a WinRT.Runtime.dll at the same version contained inside the NET SDK we're currently building on CI. -->
     <!-- 
@@ -90,11 +90,12 @@
     <PackageVersion Include="MSTest" Version="$(MSTestVersion)" />
     <PackageVersion Include="MSTest.TestFramework" Version="$(MSTestVersion)" />
     <PackageVersion Include="NJsonSchema" Version="11.4.0" />
-    <PackageVersion Include="Newtonsoft.Json" Version="13.0.3" />
+    <PackageVersion Include="Newtonsoft.Json" Version="13.0.4" />
     <PackageVersion Include="NLog" Version="5.2.8" />
     <PackageVersion Include="NLog.Extensions.Logging" Version="5.3.8" />
     <PackageVersion Include="NLog.Schema" Version="5.2.8" />
-    <PackageVersion Include="OpenAI" Version="2.5.0" />
+    <PackageVersion Include="OpenAI" Version="2.7.0" />
+    <PackageVersion Include="Polly.Core" Version="8.6.5" />
     <PackageVersion Include="ReverseMarkdown" Version="4.1.0" />
     <PackageVersion Include="RtfPipe" Version="2.0.7677.4303" />
     <PackageVersion Include="ScipBe.Common.Office.OneNote" Version="3.0.1" />
@@ -105,28 +106,28 @@
     <PackageVersion Include="StreamJsonRpc" Version="2.21.69" />
     <PackageVersion Include="StyleCop.Analyzers" Version="1.2.0-beta.556" />
     <!-- Package System.CodeDom added as a hack for being able to exclude the runtime assets so they don't conflict with 8.0.1. This is a dependency of System.Management but the 8.0.1 version wasn't published to nuget. -->
-    <PackageVersion Include="System.CodeDom" Version="10.0.7" />
+    <PackageVersion Include="System.CodeDom" Version="10.0.8" />
     <PackageVersion Include="System.CommandLine" Version="2.0.0-beta4.22272.1" />
-    <PackageVersion Include="System.ComponentModel.Composition" Version="10.0.7" />
-    <PackageVersion Include="System.Configuration.ConfigurationManager" Version="10.0.7" />
-    <PackageVersion Include="System.Data.OleDb" Version="10.0.7" />
+    <PackageVersion Include="System.ComponentModel.Composition" Version="10.0.8" />
+    <PackageVersion Include="System.Configuration.ConfigurationManager" Version="10.0.8" />
+    <PackageVersion Include="System.Data.OleDb" Version="10.0.8" />
     <!-- Package System.Diagnostics.EventLog added as a hack for being able to exclude the runtime assets so they don't conflict with 8.0.1. This is a dependency of System.Data.OleDb but the 8.0.1 version wasn't published to nuget. -->
-    <PackageVersion Include="System.Diagnostics.EventLog" Version="10.0.7" />
+    <PackageVersion Include="System.Diagnostics.EventLog" Version="10.0.8" />
     <!-- Package System.Diagnostics.PerformanceCounter added as a hack for being able to exclude the runtime assets so they don't conflict with 8.0.11. -->
-    <PackageVersion Include="System.Diagnostics.PerformanceCounter" Version="10.0.7" />
-    <PackageVersion Include="System.ClientModel" Version="1.7.0" />
-    <PackageVersion Include="System.Drawing.Common" Version="10.0.7" />
+    <PackageVersion Include="System.Diagnostics.PerformanceCounter" Version="10.0.8" />
+    <PackageVersion Include="System.ClientModel" Version="1.8.1" />
+    <PackageVersion Include="System.Drawing.Common" Version="10.0.8" />
     <PackageVersion Include="System.IO.Abstractions" Version="22.0.13" />
     <PackageVersion Include="System.IO.Abstractions.TestingHelpers" Version="22.0.13" />
-    <PackageVersion Include="System.Management" Version="10.0.7" />
+    <PackageVersion Include="System.Management" Version="10.0.8" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
-    <PackageVersion Include="System.Numerics.Tensors" Version="9.0.11" />
+    <PackageVersion Include="System.Numerics.Tensors" Version="10.0.2" />
     <PackageVersion Include="System.Private.Uri" Version="4.3.2" />
     <PackageVersion Include="System.Reactive" Version="6.0.1" />
-    <PackageVersion Include="System.Runtime.Caching" Version="10.0.7" />
-    <PackageVersion Include="System.ServiceProcess.ServiceController" Version="10.0.7" />
-    <PackageVersion Include="System.Text.Encoding.CodePages" Version="10.0.7" />
-    <PackageVersion Include="System.Text.Json" Version="10.0.7" />
+    <PackageVersion Include="System.Runtime.Caching" Version="10.0.8" />
+    <PackageVersion Include="System.ServiceProcess.ServiceController" Version="10.0.8" />
+    <PackageVersion Include="System.Text.Encoding.CodePages" Version="10.0.8" />
+    <PackageVersion Include="System.Text.Json" Version="10.0.8" />
     <PackageVersion Include="System.Text.RegularExpressions" Version="4.3.1" />
     <PackageVersion Include="ToolGood.Words.Pinyin" Version="3.1.0.3" />
     <PackageVersion Include="UnicodeInformation" Version="2.6.0" />
@@ -134,8 +135,8 @@
     <PackageVersion Include="UTF.Unknown" Version="2.6.0" />
     <PackageVersion Include="WinUIEx" Version="2.8.0" />
     <PackageVersion Include="WmiLight" Version="6.14.0" />
-    <PackageVersion Include="WPF-UI" Version="3.0.5" />
     <PackageVersion Include="WyHash" Version="1.0.5" />
+    <PackageVersion Include="YamlDotNet" Version="16.3.0" />
     <PackageVersion Include="WixToolset.Heat" Version="5.0.2" />
     <PackageVersion Include="WixToolset.Firewall.wixext" Version="5.0.2" />
     <PackageVersion Include="WixToolset.Util.wixext" Version="5.0.2" />

NOTICE.md

@@ -1600,5 +1600,5 @@ SOFTWARE.
 - UTF.Unknown
 - WinUIEx
 - WmiLight
-- WPF-UI
 - WyHash
+- YamlDotNet

PowerToys.slnx

@@ -57,6 +57,7 @@
     <Project Path="src/common/UnitTests-CommonLib/UnitTests-CommonLib.vcxproj" Id="1a066c63-64b3-45f8-92fe-664e1cce8077" />
     <Project Path="src/common/UnitTests-CommonUtils/UnitTests-CommonUtils.vcxproj" Id="8b5cfb38-ccba-40a8-ad7a-89c57b070884" />
     <Project Path="src/common/updating/updating.vcxproj" Id="17da04df-e393-4397-9cf0-84dabe11032e" />
+    <Project Path="src/common/updating/UnitTests/UpdatingUnitTests.vcxproj" Id="a1b2c3d4-e5f6-7890-abcd-ef1234567890" />
     <Project Path="src/common/version/version.vcxproj" Id="cc6e41ac-8174-4e8a-8d22-85dd7f4851df" />
   </Folder>
   <Folder Name="/common/interop/">
@@ -67,10 +68,7 @@
     <Project Path="src/common/interop/PowerToys.Interop.vcxproj" Id="f055103b-f80b-4d0c-bf48-057c55620033" />
   </Folder>
   <Folder Name="/common/log/">
-    <Project Path="src/common/logger/logger.vcxproj" Id="d9b8fc84-322a-4f9f-bbb9-20915c47ddfd">
-      <BuildDependency Project="src/logging/logging.vcxproj" />
-    </Project>
-    <Project Path="src/logging/logging.vcxproj" Id="7e1e3f13-2bd6-3f75-a6a7-873a2b55c60f" />
+    <Project Path="src/common/logger/logger.vcxproj" Id="d9b8fc84-322a-4f9f-bbb9-20915c47ddfd" />
   </Folder>
   <Folder Name="/common/notifications/">
     <Project Path="src/common/notifications/BackgroundActivator/BackgroundActivator.vcxproj" Id="0b593a6c-4143-4337-860e-db5710fb87db" />
@@ -470,6 +468,12 @@
       <Platform Solution="*|x64" Project="x64" />
     </Project>
   </Folder>
+  <Folder Name="/modules/DesktopGrass/">
+    <Project Path="src/modules/DesktopGrass/DesktopGrass.Native/DesktopGrass.Native.vcxproj" Id="b0d4e1b0-1f5e-4c2d-9f44-da8c3f1a2a11" />
+  </Folder>
+  <Folder Name="/modules/DesktopGrass/Tests/">
+    <Project Path="src/modules/DesktopGrass/DesktopGrass.Native.Tests/DesktopGrass.Native.Tests.vcxproj" />
+  </Folder>
   <Folder Name="/modules/imageresizer/">
     <Project Path="src/modules/imageresizer/dll/ImageResizerExt.vcxproj" Id="0b43679e-edfa-4da0-ad30-f4628b308b1b" />
     <Project Path="src/modules/imageresizer/ImageResizerCLI/ImageResizerCLI.csproj">
@@ -801,6 +805,14 @@
     <Project Path="src/modules/peek/peek/peek.vcxproj" Id="a1425b53-3d61-4679-8623-e64a0d3d0a48" />
   </Folder>
   <Folder Name="/modules/PowerAccent/">
+    <Project Path="src/modules/poweraccent/PowerAccent.Common.UnitTests/PowerAccent.Common.UnitTests.csproj">
+      <Platform Solution="*|ARM64" Project="ARM64" />
+      <Platform Solution="*|x64" Project="x64" />
+    </Project>
+    <Project Path="src/modules/poweraccent/PowerAccent.Common/PowerAccent.Common.csproj">
+      <Platform Solution="*|ARM64" Project="ARM64" />
+      <Platform Solution="*|x64" Project="x64" />
+    </Project>
     <Project Path="src/modules/poweraccent/PowerAccent.Core/PowerAccent.Core.csproj">
       <Platform Solution="*|ARM64" Project="ARM64" />
       <Platform Solution="*|x64" Project="x64" />
@@ -989,9 +1001,16 @@
       <Platform Solution="*|x64" Project="x64" />
     </Project>
   </Folder>
-  <Folder Name="/modules/shortcutguide/">
-    <Project Path="src/modules/ShortcutGuide/ShortcutGuide/ShortcutGuide.vcxproj" Id="2edb3eb4-fa92-4bff-b2d8-566584837231" />
-    <Project Path="src/modules/ShortcutGuide/ShortcutGuideModuleInterface/ShortcutGuideModuleInterface.vcxproj" Id="2d604c07-51fc-46bb-9eb7-75aecc7f5e81" />
+  <Folder Name="/modules/ShortcutGuide/">
+    <Project Path="src/modules/ShortcutGuide/ShortcutGuide.IndexYmlGenerator/ShortcutGuide.IndexYmlGenerator.csproj">
+      <Platform Solution="*|ARM64" Project="ARM64" />
+      <Platform Solution="*|x64" Project="x64" />
+    </Project>
+    <Project Path="src/modules/ShortcutGuide/ShortcutGuide.Ui/ShortcutGuide.Ui.csproj">
+      <Platform Solution="*|ARM64" Project="ARM64" />
+      <Platform Solution="*|x64" Project="x64" />
+    </Project>
+    <Project Path="src/modules/ShortcutGuide/ShortcutGuideModuleInterface/ShortcutGuideModuleInterface.vcxproj" Id="e487304a-b1fb-4e6b-8e70-014051af5b99" />
   </Folder>
   <Folder Name="/modules/Workspaces/">
     <Project Path="src/modules/Workspaces/Workspaces.ModuleServices/Workspaces.ModuleServices.csproj">
@@ -1126,3 +1145,5 @@
   <Project Path="src/Update/PowerToys.Update.vcxproj" Id="44ce9ae1-4390-42c5-bacc-0fd6b40aa203" />
   <Project Path="tools/project_template/ModuleTemplate/ModuleTemplateCompileTest.vcxproj" Id="64a80062-4d8b-4229-8a38-dfa1d7497749" />
 </Solution>
+
+

deps/expected.props

@@ -1,7 +0,0 @@
-<Project>
-	<ItemDefinitionGroup>
-		<ClCompile>
-			<AdditionalIncludeDirectories>$(MSBuildThisFileDirectory)expected-lite\include\nonstd\;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-		</ClCompile>
-	</ItemDefinitionGroup>
-</Project>

deps/spdlog-msvc-fix/include/spdlog-msvc-fix.h

@@ -1,94 +0,0 @@
-// spdlog-msvc-fix.h
-//
-// Workaround for MSVC 14.51 (compiler version 19.51, _MSC_VER >= 1951) removing
-// stdext::checked_array_iterator. Force-included for all spdlog consumers via
-// deps/spdlog.props, because spdlog v1.8.5's bundled fmt format.h(357) still
-// references this type inside #if defined(_SECURE_SCL) && _SECURE_SCL -- a
-// branch entered in Debug builds where _ITERATOR_DEBUG_LEVEL > 0.
-//
-// On MSVC 14.50 and earlier, the type still exists in <iterator>, so this shim
-// is a no-op via the _MSC_VER guard. On MSVC 14.51+, it provides a minimal
-// pointer-backed substitute that satisfies the bundled fmt's usage:
-//
-//   template <typename T> using checked_ptr = stdext::checked_array_iterator<T*>;
-//   template <typename T> checked_ptr<T> make_checked(T* p, size_t size) {
-//     return {p, size};
-//   }
-//   ... return make_checked(get_data(c) + size, n);
-//
-// When deps/spdlog is bumped past v1.14 (which ships fmt 10.2 and drops this
-// dependency), this shim and its <ForcedIncludeFiles> entry in deps/spdlog.props
-// can be deleted.
-
-#pragma once
-
-#if defined(__cplusplus) && defined(_MSC_VER) && _MSC_VER >= 1951
-
-#include <cstddef>
-#include <iterator>
-#include <type_traits>
-
-namespace stdext
-{
-    template <typename _Ptr>
-    class checked_array_iterator
-    {
-        _Ptr _Myarray = nullptr;
-        std::size_t _Mysize = 0;
-        std::size_t _Myindex = 0;
-
-    public:
-        using iterator_category = std::random_access_iterator_tag;
-        using value_type = std::remove_cv_t<std::remove_pointer_t<_Ptr>>;
-        using difference_type = std::ptrdiff_t;
-        using pointer = _Ptr;
-        using reference = std::remove_pointer_t<_Ptr>&;
-
-        constexpr checked_array_iterator() = default;
-
-        constexpr checked_array_iterator(_Ptr arr, std::size_t size, std::size_t idx = 0) noexcept
-            : _Myarray(arr), _Mysize(size), _Myindex(idx)
-        {
-        }
-
-        constexpr reference operator*() const noexcept { return _Myarray[_Myindex]; }
-        constexpr pointer operator->() const noexcept { return _Myarray + _Myindex; }
-        constexpr reference operator[](difference_type n) const noexcept
-        {
-            return _Myarray[_Myindex + static_cast<std::size_t>(n)];
-        }
-
-        constexpr checked_array_iterator& operator++() noexcept { ++_Myindex; return *this; }
-        constexpr checked_array_iterator operator++(int) noexcept { auto t = *this; ++_Myindex; return t; }
-        constexpr checked_array_iterator& operator--() noexcept { --_Myindex; return *this; }
-        constexpr checked_array_iterator operator--(int) noexcept { auto t = *this; --_Myindex; return t; }
-
-        constexpr checked_array_iterator& operator+=(difference_type n) noexcept
-        {
-            _Myindex = static_cast<std::size_t>(static_cast<difference_type>(_Myindex) + n);
-            return *this;
-        }
-        constexpr checked_array_iterator& operator-=(difference_type n) noexcept
-        {
-            _Myindex = static_cast<std::size_t>(static_cast<difference_type>(_Myindex) - n);
-            return *this;
-        }
-
-        friend constexpr checked_array_iterator operator+(checked_array_iterator it, difference_type n) noexcept { it += n; return it; }
-        friend constexpr checked_array_iterator operator+(difference_type n, checked_array_iterator it) noexcept { return it + n; }
-        friend constexpr checked_array_iterator operator-(checked_array_iterator it, difference_type n) noexcept { it -= n; return it; }
-        friend constexpr difference_type operator-(checked_array_iterator a, checked_array_iterator b) noexcept
-        {
-            return static_cast<difference_type>(a._Myindex) - static_cast<difference_type>(b._Myindex);
-        }
-
-        friend constexpr bool operator==(checked_array_iterator a, checked_array_iterator b) noexcept { return a._Myindex == b._Myindex; }
-        friend constexpr bool operator!=(checked_array_iterator a, checked_array_iterator b) noexcept { return !(a == b); }
-        friend constexpr bool operator<(checked_array_iterator a, checked_array_iterator b) noexcept { return a._Myindex < b._Myindex; }
-        friend constexpr bool operator>(checked_array_iterator a, checked_array_iterator b) noexcept { return b < a; }
-        friend constexpr bool operator<=(checked_array_iterator a, checked_array_iterator b) noexcept { return !(b < a); }
-        friend constexpr bool operator>=(checked_array_iterator a, checked_array_iterator b) noexcept { return !(a < b); }
-    };
-} // namespace stdext
-
-#endif // __cplusplus && _MSC_VER >= 1951

deps/spdlog.props

@@ -1,9 +1,14 @@
+<?xml version="1.0" encoding="utf-8"?>
 <Project>
-	<ItemDefinitionGroup>
-		<ClCompile>
-			<AdditionalIncludeDirectories>$(MSBuildThisFileDirectory)spdlog\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
-			<PreprocessorDefinitions>SPDLOG_WCHAR_TO_UTF8_SUPPORT;SPDLOG_COMPILED_LIB;SPDLOG_WCHAR_FILENAMES;%(PreprocessorDefinitions)</PreprocessorDefinitions>
-			<ForcedIncludeFiles>$(MSBuildThisFileDirectory)spdlog-msvc-fix\include\spdlog-msvc-fix.h;%(ForcedIncludeFiles)</ForcedIncludeFiles>
-		</ClCompile>
-	</ItemDefinitionGroup>
+  <!--
+    SPDLOG_* preprocessor defines for spdlog consumers. The actual vcpkg
+    integration (VcpkgEnabled, VcpkgRoot, triplet, manifest install) lives
+    in Cpp.Build.props; this file just carries the defines that match how
+    the pre-vcpkg in-tree build was configured.
+  -->
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <PreprocessorDefinitions>SPDLOG_WCHAR_TO_UTF8_SUPPORT;SPDLOG_COMPILED_LIB;SPDLOG_WCHAR_FILENAMES;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
 </Project>

deps/vcpkg-overlays/spdlog/msvc-14.51-stdext-checked-array-iterator.patch

@@ -0,0 +1,16 @@
+--- a/include/spdlog/fmt/bundled/format.h
++++ b/include/spdlog/fmt/bundled/format.h
+@@ -354,7 +354,12 @@ inline typename Container::value_type* get_data(Container& c) {
+   return c.data();
+ }
+ 
+-#if defined(_SECURE_SCL) && _SECURE_SCL
++// PowerToys: stdext::checked_array_iterator was deprecated in VS 2019 16.10
++// and removed entirely in MSVC 14.51 (compiler 19.51, _MSC_VER >= 1951;
++// see microsoft/STL STL4043). Skip the broken branch on those toolsets so the
++// pointer-based fallback below is used instead. Drop this guard once
++// deps/spdlog is bumped past v1.14 (which ships fmt 10.2 and removes this code).
++#if defined(_SECURE_SCL) && _SECURE_SCL && (!defined(_MSC_VER) || _MSC_VER < 1951)
+ // Make a checked iterator to avoid MSVC warnings.
+ template <typename T> using checked_ptr = stdext::checked_array_iterator<T*>;
+ template <typename T> checked_ptr<T> make_checked(T* p, size_t size) {

deps/vcpkg-overlays/spdlog/portfile.cmake

@@ -0,0 +1,43 @@
+# PowerToys overlay port for spdlog.
+#
+# Pinned to the same git commit that the deleted deps/spdlog submodule pointed
+# at, so this is a 1:1 submodule->vcpkg migration with no version change
+# (per the maintainer guidance: convert one submodule at a time, atomic
+# commit, don't also bump the version).
+#
+# A single hunk patch works around MSVC 14.51 STL4043 (removal of
+# stdext::checked_array_iterator) in spdlog's bundled fmt 7. Drop this overlay
+# (and switch to upstream vcpkg's spdlog port) once PowerToys bumps spdlog
+# past v1.14, which ships fmt 10.2 and removes the affected code path.
+
+vcpkg_from_github(
+    OUT_SOURCE_PATH SOURCE_PATH
+    REPO gabime/spdlog
+    REF 616866fcf40340ea25a8f218369bad810ef58e72
+    SHA512 2076c527c7768627e6856b2f7ef663b185fd6251894cffd9299203d00f3d2de5696461060442dd72b96c9d3f0fd27f7f63ad2edfdf295e9b06c5fac6d6212faf
+    HEAD_REF v1.x
+    PATCHES
+        msvc-14.51-stdext-checked-array-iterator.patch
+)
+
+vcpkg_cmake_configure(
+    SOURCE_PATH "${SOURCE_PATH}"
+    OPTIONS
+        -DSPDLOG_BUILD_EXAMPLE=OFF
+        -DSPDLOG_BUILD_TESTS=OFF
+        -DSPDLOG_BUILD_BENCH=OFF
+        -DSPDLOG_FMT_EXTERNAL=OFF
+        -DSPDLOG_WCHAR_SUPPORT=ON
+        -DSPDLOG_WCHAR_FILENAMES=ON
+        -DSPDLOG_NO_EXCEPTIONS=OFF
+        -DSPDLOG_BUILD_SHARED=OFF
+)
+
+vcpkg_cmake_install()
+vcpkg_cmake_config_fixup(PACKAGE_NAME spdlog CONFIG_PATH lib/cmake/spdlog)
+vcpkg_fixup_pkgconfig()
+vcpkg_copy_pdbs()
+
+file(REMOVE_RECURSE "${CURRENT_PACKAGES_DIR}/debug/include")
+
+vcpkg_install_copyright(FILE_LIST "${SOURCE_PATH}/LICENSE")

deps/vcpkg-overlays/spdlog/vcpkg.json

@@ -0,0 +1,18 @@
+{
+  "name": "spdlog",
+  "version-string": "1.8.5-pt-616866fc",
+  "port-version": 0,
+  "description": "Very fast, header-only/compiled, C++ logging library. PowerToys overlay pinned to gabime/spdlog@616866fc (the exact submodule commit before this migration), with a single-hunk patch that works around MSVC 14.51 removing stdext::checked_array_iterator (STL4043).",
+  "homepage": "https://github.com/gabime/spdlog",
+  "license": "MIT",
+  "dependencies": [
+    {
+      "name": "vcpkg-cmake",
+      "host": true
+    },
+    {
+      "name": "vcpkg-cmake-config",
+      "host": true
+    }
+  ]
+}

doc/devdocs/development/debugging.md

@@ -97,6 +97,10 @@ The Shell Process Debugging Tool is a Visual Studio extension that helps debug m
 - Check Event Viewer for application crashes related to `PowerToys.Settings.exe`
 - Crash dumps can be obtained from Event Viewer
 
+### Debugging Command Palette
+Command Palette can be easily debugged using the solution filter in `src/modules/cmdpal/Command Palette.slnf`. This will open Command Palette as its own Visual Studio solution that can be run and debugged directly in Visual Studio without the need for the Shell Process Debugging Tool.
+
+
 ## Troubleshooting Build Errors
 
 ### Missing Image Files or Corrupted Build State

doc/devdocs/modules/shortcut_guide.md

@@ -9,12 +9,14 @@
 [Pull Requests](https://github.com/microsoft/PowerToys/pulls?q=is%3Apr+is%3Aopen+label%3A%22Product-Shortcut+Guide%22+)
 
 ## Overview
-Shortcut Guide is a PowerToy that displays an overlay of available keyboard shortcuts when the Windows key is pressed and held. It provides a visual reference for Windows key combinations, helping users discover and utilize built-in Windows shortcuts.
+Shortcut Guide is a PowerToy that displays an overlay of available keyboard shortcuts when a user-set keyboard shortcut is pressed. It helps users discover and remember keyboard shortcuts for Windows and apps.
+
+> [!NOTE]
+> The spec for the manifest files is in development and will be linked here once available.
 
 ## Usage
-- Press and hold the Windows key to display the overlay of available shortcuts
-- Press the hotkey again to dismiss the overlay
-- The overlay displays Windows shortcuts with their corresponding actions
+- Press the user-defined hotkey to display the overlay
+- Press the hotkey again or press ESC to dismiss the overlay
 
 ## Build and Debug Instructions
 
@@ -25,67 +27,89 @@ Shortcut Guide is a PowerToy that displays an overlay of available keyboard shor
 4. The executable is named PowerToys.ShortcutGuide.exe
 
 ### Debug
-1. Right-click the ShortcutGuide project and select 'Set as Startup Project'
+1. Right-click the ShortcutGuide.Ui project and select 'Set as Startup Project'
 2. Right-click the project again and select 'Debug'
 
-## Code Structure
+> [!NOTE]
+> When run in debug mode, the window behaves differently than in release mode. It will not automatically close when loosing focus, it will be displayed on top of all other windows, and it is not hidden from the taskbar. 
 
-![Diagram](../images/shortcutguide/diagram.png)
+## Project Structure
 
-### Core Files
+The Shortcut Guide module consists of the following 4 projects:
 
-#### [`dllmain.cpp`](/src/modules/shortcut_guide/dllmain.cpp)
-Contains DLL boilerplate code. Implements the PowertoyModuleIface, including enable/disable functionality and GPO policy handling. Captures hotkey events and starts the PowerToys.ShortcutGuide.exe process to display the shortcut guide window.
+### [`ShortcutGuide.Ui`](/src/modules/ShortcutGuide/ShortcutGuide.Ui/ShortcutGuide.Ui.csproj
 
-#### [`shortcut_guide.cpp`](/src/modules/shortcut_guide/shortcut_guide.cpp)
-Contains the module interface code. It initializes the settings values and the keyboard event listener. Defines the OverlayWindow class, which manages the overall logic and event handling for the PowerToys Shortcut Guide.
+This is the main UI project for the Shortcut Guide module. Upon startup it does the following tasks:
 
-#### [`overlay_window.cpp`](/src/modules/shortcut_guide/overlay_window.cpp)
-Contains the code for loading the SVGs, creating and rendering of the overlay window. Manages and displays overlay windows with SVG graphics through two main classes:
-- D2DOverlaySVG: Handles loading, resizing, and manipulation of SVG graphics
-- D2DOverlayWindow: Manages the display and behavior of the overlay window
+1. Copies the built-in manifest files to the users manifest directory (overwriting existing files).
+2. Generate the `index.yml` manifest file.
+3. Populate the PowerToys shortcut manifest with the user-defined shortcuts.
+4. Starts the UI.
 
-#### [`keyboard_state.cpp`](/src/modules/shortcut_guide/keyboard_state.cpp)
-Contains helper methods for checking the current state of the keyboard.
+### Related files in PowerToys.Interop
 
-#### [`target_state.cpp`](/src/modules/shortcut_guide/target_state.cpp)
-State machine that handles the keyboard events. It's responsible for deciding when to show the overlay, when to suppress the Start menu (if the overlay is displayed long enough), etc. Handles state transitions and synchronization to ensure the overlay is shown or hidden appropriately based on user interactions.
+#### [`excluded_app.cpp`](/src/modules/ShortcutGuide/ShortcutGuide.CPPProject/excluded_app.cpp)
 
-#### [`trace.cpp`](/src/modules/shortcut_guide/trace.cpp)
-Contains code for telemetry.
+This file contains one function with the following signature:
 
-### Supporting Files
+```cpp
+__declspec(dllexport) bool IsCurrentWindowExcludedFromShortcutGuide()
+```
 
-#### [`animation.cpp`](/src/modules/shortcut_guide/animation.cpp)
-Handles the timing and interpolation of animations. Calculates the current value of an animation based on elapsed time and a specified easing function.
+This function checks if the current window is excluded from the Shortcut Guide overlay. It returns `true` if the current window is excluded otherwise it returns `false`.
 
-#### [`d2d_svg.cpp`](/src/modules/shortcut_guide/d2d_svg.cpp)
-Provides functionality for loading, resizing, recoloring, rendering, and manipulating SVG images using Direct2D.
+#### [`tasklist_positions.cpp`](/src/modules/ShortcutGuide/ShortcutGuide.CPPProject/tasklist_positions.cpp)
 
-#### [`d2d_text.cpp`](/src/modules/shortcut_guide/d2d_text.cpp)
-Handles creation, resizing, alignment, and rendering of text using Direct2D and DirectWrite.
+This file contains helper functions to retrieve the positions of the taskbar buttons. It exports the following function:
 
-#### [`d2d_window.cpp`](/src/modules/shortcut_guide/d2d_window.cpp)
-Manages a window using Direct2D and Direct3D for rendering. Handles window creation, resizing, rendering, and destruction.
+```cpp
+__declspec(dllexport) TasklistButton* get_buttons(HMONITOR monitor, int* size)
+```
 
-#### [`native_event_waiter.cpp`](/src/modules/shortcut_guide/native_event_waiter.cpp)
-Waits for a named event and executes a specified action when the event is triggered. Uses a separate thread to handle event waiting and action execution.
+This function retrieves the positions of the taskbar buttons for a given monitor. It returns an array of `TasklistButton` structures (max 10), which contain the position and size of each button.
 
-#### [`tasklist_positions.cpp`](/src/modules/shortcut_guide/tasklist_positions.cpp)
-Handles retrieving and updating the positions and information of taskbar buttons in Windows.
+`monitor` must be the monitor handle of the monitor containing the taskbar instance of which the buttons should be retrieved.
 
-#### [`main.cpp`](/src/modules/shortcut_guide/main.cpp)
-The entry point for the PowerToys Shortcut Guide application. Handles initialization, ensures single instance execution, manages parent process termination, creates and displays the overlay window, and runs the main event loop.
+`size` will contain the resulting array size.
+
+It determines the positions through Windows `FindWindowEx` function.
+For the primary taskbar it searches for:
+* A window called "Shell_TrayWnd"
+* that contains a window called "ReBarWindow32"
+* that contains a window called "MSTaskSwWClass"
+* that contains a window called "MSTaskListWClass"
+
+For any secondary taskbar it searches for:
+* A window called "Shell_SecondaryTrayWnd"
+* that contains a window called "WorkerW"
+* that contains a window called "MSTaskListWClass"
+
+It then enumerates all the button elements inside "MSTaskListWClass" while skipping such with a same name (which implies the user does not use combining taskbar buttons) 
+
+If this method fails, which it will for newer versions of Windows, it falls back to searching for:
+* A window called "Shell_TrayWnd" or "Shell_SecondaryTrayWnd"
+* that contains a window called "Windows.UI.Composition.DesktopWindowContentBridge"
+* that contains a window called "Windows.UI.Input.InputSite.WindowClass"
+* the first child element
+
+It then enumerates all the button elements inside the selected while skipping such with a same name (which implies the user does not use combining taskbar buttons) and such that do not start with "Appid:" (which are not actual taskbar buttons related to apps, but others like the widgets or the search button).
+
+### [`ShortcutGuide.IndexYmlGenerator`](/src/modules/ShortcutGuide/ShortcutGuide.IndexYmlGenerator/)
+
+This application generates the `index.yml` manifest file.
+
+It is a separate project so that its code can be easier ported to WinGet in the future.
+
+### [`ShortcutGuideModuleInterface`](/src/modules/ShortcutGuide/ShortcutGuideModuleInterface/ShortcutGuideModuleInterface.vcxproj)
+
+The module interface that handles opening and closing the user interface.
 
 ## Features and Limitations
 
-- The overlay displays Windows shortcuts (Windows key combinations)
-- The module supports localization, but only for the Windows controls on the left side of the overlay
+- Currently the displayed shortcuts (Except the ones from PowerToys) are not localized.
 - It's currently rated as a P3 (lower priority) module
 
 ## Future Development
 
-A community-contributed version 2 is in development that will support:
-- Application-specific shortcuts based on the active application
-- Additional shortcuts beyond Windows key combinations
-- PowerToys shortcuts
+- Implementing with WinGet to get new shortcut manifest files
+- Adding localization support for the built-in manifest files

doc/specs/WinGet Manifest Keyboard Shortcuts schema.md

@@ -0,0 +1,318 @@
+# WinGet Manifest Keyboard Shortcuts schema
+
+## 1 What this spec is about
+
+This spec provides an extension to the existing [WinGet manifest schema](https://github.com/microsoft/winget-pkgs/blob/master/doc/manifest/README.md) in form of an additional yaml file, that describes keyboard shortcuts the application provides.
+
+These yaml files are saved on a per-user base and so called manifest interpreters can then display these manifests in a human-friendly version.
+
+### 1.1 What this spec is not about
+
+This spec does not provide a way to back up or save user-defined keyboard shortcuts.
+
+## 2 Save location of manifests
+
+### 2.1 WinGet 
+
+These files are saved online along with the other manifest files in the [WinGet Package repository](https://github.com/microsoft/winget-pkgs).
+
+### 2.2 Locally
+
+All manifests and one index file are saved locally under `%LocalAppData%/Microsoft/WinGet/KeyboardShortcuts`. All apps are allowed to add their manifest files there. In addition Package Managers (like WinGet) and manifest interpreters (like PowerToys Shortcut Guide) can control and add other manifests themselves.
+
+#### 2.2.1 Downloading manifests
+
+When WinGet or other package managers download a package, they should also download the corresponding keyboard shortcuts manifest file and save it in the local directory, given such a file exists in the WinGet repository.
+
+The downloader is also responsible for updating the local `index.yaml` file, which contains all the information about the different manifest files that are saved in the same directory.
+
+#### 2.2.2 Updating manifests
+
+When a manifest interpreter starts, it should download the latest version of the manifests from the WinGet repository and save them in the local directory. If a manifest interpreter is not able to download the manifests or they do not exist, it should use the locally saved manifests.
+
+The updater is also responsible for updating the local `index.yaml` file, which contains all the information about the different manifest files that are saved in the same directory.
+
+> Note: WinGet must provide a way to update the keyboard shortcuts manifests given a package id.
+
+### 2.3 File names
+
+The file name of a keyboard shortcuts file is the WinGet package identifier, plus the locale of the strings of the file and at last the `.KBSC.yaml` file extension.
+
+For example the package "test.bar" saves its manifest with `en-US` strings in `test.bar.en-US.KBSC.yaml`.
+
+#### 2.3.1 No winget package available
+
+If an application has no corresponding WinGet package its name starts with a plus (`+`) symbol.
+
+### 2.4 Reserved namespaces
+
+Every name starting with `+WindowsNT` is reserved for the Windows OS and its components.
+
+## 3 File syntax
+
+All relevant files are written in [YAML](https://yaml.org/spec).
+
+> Note: A JSON schema will be provided as soon as the spec reaches a further step
+
+### 3.1 Manifest Schema vNext Keyboard Shortcuts File
+
+```
+PackageName:                # The package unique identifier
+WindowFilter:               # The filter of window processes to which the shortcuts apply to
+BackgroundProcess:          # Optionally allows applying WindowFilter to background processes
+Shortcuts:                  # List of sections with keyboard shortcuts
+  - SectionName:            # Name of the category of shortcuts
+    Properties:             # List of shortcuts in the category
+      - Name:               # Name of the shortcut
+        Description:        # Optional description of the shortcut
+        AdditionalInfo:     # Optional additional information about the shortcut
+        Recommended:        # Optionally determines if the shortcut is displayed in a designated recommended area
+        Shortcut:           # An array of shortcuts that need to be pressed
+          - Win:            # Determines if the Windows Key is part of the shortcut
+            Ctrl:           # Determines if the Ctrl Key is part of the shortcut
+            Shift:          # Determines if the Shift Key is part of the shortcut
+            Alt:            # Determines if the Alt Key is part of the shortcut
+            Keys:           # Array of keys that need to be pressed
+```
+
+Per Application/Package one or more Keyboard manifests can be declared. Every manifest must have a different locale and the same `PackageName`, `WindowFilter` and `BackgroundProcess` fields.
+
+<details>
+ <summary><b>PackageName</b> - The package unique identifier</summary>
+
+ Package identifier (see 2.1 for more information on the package identifier).
+
+</details>
+
+<details>
+ <summary><b>WindowFilter</b> - The filter of window processes to which the shortcuts apply to</summary>
+
+ This field declares for which process name the shortcuts should be shown (To rephrase: For which processes the shortcut will have an effect if pressed). The value can be either an exact process executable name, for example `explorer.exe` or `chrome.exe`, or a single asterisk (`*`) to apply to any process. No other wildcard patterns are supported by this specification.
+
+</details>
+
+<details>
+ <summary><b>BackgroundProcess</b> - Optionally allows applying WindowFilter to background processes.</summary>
+
+ **Optional field**
+
+ Defaults to `False`. Determines if WindowFilter should apply to background processes as well (Rephrased: When the process is running, the shortcuts will apply).
+
+</details>
+
+<details>
+ <summary><b>Shortcuts</b> - List of sections with keyboard shortcuts</summary>
+ 
+ List of different section (also called categories) of shortcuts.
+</details>
+
+<details>
+ <summary><b>SectionName</b> - Name of the category of shortcuts</summary>
+
+ Name of the section of shortcuts. 
+
+**Special sections**:
+
+Special sections start with an identifier enclosed between `<` and `>`. This declares the category as a special display. If the interpreter of the manifest file can't understand the content this section should be left out.
+
+</details>
+
+<details>
+ <summary><b>Properties</b> - List of shortcuts in the category</summary>
+</details>
+
+<details>
+ <summary><b>Name</b> - Name of the shortcut</summary>
+
+ Name of the shortcut. This is the name that will be displayed in the interpreter.
+
+</details>
+
+
+<details>
+ <summary><b>Description</b> - Optional description of the shortcut</summary>
+
+ Optional description of the shortcut. This is the description that will be displayed by the interpreter.
+</details>
+
+<details>
+ <summary><b>AdditionalInfo</b> - Optional additional information about the shortcut</summary>
+
+ Array of additional information about the shortcut. This is the additional information that will be displayed by the interpreter and are not part of this manifest.
+
+ **Example**:
+
+ For example, if the shortcut is only available on a certain Windows version, this information could be added here.
+ ```yaml
+  AdditionalInfo:
+    - MinWindowsVersion: "10.0.19041.0"
+  ```
+</details>
+
+<details>
+ <summary><b>Shortcut</b> - An array of shortcuts that need to be pressed</summary>
+
+  An array of shortcuts that need to be pressed. This allows defining sequential shortcuts that need to be pressed in order to trigger the action.
+
+</details>
+
+<details>
+ <summary><b>Win</b> - Determines if the Windows Key is part of the shortcut</summary>
+
+ Refers to the left Windows Key on the keyboard.
+</details>
+
+<details>
+ <summary><b>Ctrl</b> - Determines if the Ctrl Key is part of the shortcut</summary>
+
+ Refers to the left Ctrl Key on the keyboard.
+</details>
+
+<details>
+ <summary><b>Shift</b> - Determines if the Shift Key is part of the shortcut</summary>
+
+ Refers to the left Shift Key on the keyboard.
+</details>
+
+<details>
+ <summary><b>Alt</b> - Determines if the Alt Key is part of the shortcut</summary>
+
+  Refers to the left Alt Key on the keyboard.
+</details>
+
+
+<details>
+ <summary><b>Recommended</b> - Optionally determines if the shortcut is displayed in a designated recommended area</summary>
+
+ **Optional field**
+
+ Defaults to `False`. Determines if the shortcut should be displayed in a designated recommended area. This is a visual hint for the user that this shortcut is important.
+
+</details>
+
+<details>
+ <summary><b>Keys</b> - Array of keys that need to be pressed</summary>
+
+ A string array of all the keys that need to be pressed. If a number is supplied, it should be read as a [KeyCode](https://learn.microsoft.com/windows/win32/inputdev/virtual-key-codes) and displayed accordingly (based on the Keyboard Layout of the user).
+
+**Special keys**:
+
+Special keys are enclosed between `<` and `>` and correspond to a key that should be displayed in a certain way. If the interpreter of the manifest file can't understand the content, the brackets should be left out.
+
+|Name|Description|
+|----|-----------|
+|`<Office>`| Corresponds to the Office key on some Windows keyboards |
+|`<Copilot>`| Corresponds to the Copilot key on some Windows keyboards |
+|`<Left>`| Corresponds to the left arrow key |
+|`<Right>`| Corresponds to the right arrow key |
+|`<Up>`| Corresponds to the up arrow key |
+|`<Down>`| Corresponds to the down arrow key |
+|`<Enter>`| Corresponds to the Enter key |
+|`<Space>`| Corresponds to the Space key |
+|`<Tab>`| Corresponds to the Tab key |
+|`<Backspace>`| Corresponds to the Backspace key |
+|`<Delete>`| Corresponds to the Delete key |
+|`<Insert>`| Corresponds to the Insert key |
+|`<Home>`| Corresponds to the Home key |
+|`<End>`| Corresponds to the End key |
+|`<PrtScr>`| Corresponds to the Print Screen key |
+|`<Pause>`| Corresponds to the pause key |
+|`<PageUp>`| Corresponds to the Page Up key |
+|`<PageDown>`| Corresponds to the Page Down key |
+|`<Escape>`| Corresponds to the Escape key |
+|`<Arrow>`| Corresponds to either the left, right, up or down arrow key |
+|`<ArrowLR>`| Corresponds to either the left or right arrow key |
+|`<ArrowUD>`| Corresponds to either the up or down arrow key |
+|`<Underlined letter>`| Corresponds to any letter that is _underlined_ in the UI |
+
+</details>
+
+#### 3.2.2 Example
+
+```yaml
+PackageName: Microsoft.PowerToys
+WindowFilter: "*"
+BackgroundProcess: True
+Shortcuts:
+  - SectionName: General
+    Properties:
+      - Name: Advanced Paste
+        Shortcut:
+          - Win: True
+            Ctrl: False
+            Alt: False
+            Shift: False
+            Keys:
+              - 86
+        Description: Open Advanced Paste window
+      - Name: Advanced Paste
+        Shortcut:
+          - Win: True
+            Ctrl: True
+            Alt: True
+            Shift: False
+            Keys:
+              - 86
+        Description: Paste as plain text directly
+
+```
+
+
+### 3.2 `index.yaml` file
+
+The `index.yaml` file is a file that contains all the information about the different manifest files that are saved in the same directory. This file is only available locally and is not saved in the WinGet repository as it is specific to the user.
+
+```yaml
+DefaultShellName:           # The package identifier of the default shell used in Windows
+Index:                      # List of all manifest files
+  - WindowFilter:           # The filter of window processes to which the shortcuts apply to
+    BackgroundProcess:      # Optionally allows applying WindowFilter to background processes
+    Apps:                   # List of all manifest files for the filter
+```
+
+<details>
+ <summary><b>DefaultShellName</b> - The package identifier of the default shell used in Windows</summary>
+  
+ This declares the package identifier of the default shell used in Windows. Most commonly it is `+WindowsNT.Shell`. Although not enforced, only the shell declared in the registry key `HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon\Shell` should be used here.
+
+</details>
+
+<details>
+ <summary><b>Index</b> - List of all manifest files</summary>
+</details>
+
+<details>
+ <summary><b>WindowFilter</b> - The filter of window processes to which the shortcuts apply to</summary>
+
+ See the `WindowFilter` field in the manifest file for more information.
+
+</details>
+
+<details>
+ <summary><b>BackgroundProcess</b> - Optionally allows applying WindowFilter to background processes</summary>
+ 
+ **Optional field**
+
+ See the `BackgroundProcess` field in the manifest file for more information.
+
+</details>
+
+<details>
+ <summary><b>Apps</b> - List of all the package identifiers applying for the filter</summary>
+</details>
+
+#### 3.2.1 Example
+
+```yaml
+DefaultShellName: "+WindowsNT.Shell"
+Index:
+  - Filter: "*"
+    BackgroundProcess: True
+    Apps: ["+WindowsNT.Shell", "Microsoft.PowerToys"]
+  - Filter: "explorer.exe"
+    Apps: ["+WindowsNT.WindowsExplorer"]
+  - Filter: "taskmgr.exe"
+    Apps: ["+WindowsNT.TaskManager"]
+  - Filter: "msedge.exe"
+    Apps: ["+WindowsNT.Edge"]
+```

doc/thirdPartyRunPlugins.md

@@ -79,3 +79,4 @@ Below are community created plugins that target a website or software.  They are
 | [Linear](https://github.com/vednig/powertoys-linear) | [vednig](https://github.com/vednig) | Create Linear Issues directly from Powertoys Run |
 | [PerplexitySearchShortcut](https://github.com/0x6f677548/PowerToys-Run-PerplexitySearchShortcut) | [0x6f677548](https://github.com/0x6f677548) | Search Perplexity |
 | [SpeedTest](https://github.com/ruslanlap/PowerToysRun-SpeedTest) | [ruslanlap](https://github.com/ruslanlap) | One-command internet speed tests with real-time results, modern UI, and shareable links. |
+| [DiskAnalyzer](https://github.com/thetsaw/PowerToys.Plugin) | [thetsaw](https://github.com/thetsaw) | Scan folders, find the largest files, and view drive space usage with visual progress bars. |

installer/PowerToysSetup.slnx

@@ -8,9 +8,6 @@
   </Project>
   <Project Path="../src/common/Telemetry/EtwTrace/EtwTrace.vcxproj" Id="8f021b46-362b-485c-bfba-ccf83e820cbd" />
   <Project Path="../src/common/version/version.vcxproj" Id="cc6e41ac-8174-4e8a-8d22-85dd7f4851df" />
-  <Project Path="../src/logging/logging.vcxproj" Id="7e1e3f13-2bd6-3f75-a6a7-873a2b55c60f">
-    <Build Solution="Debug|ARM64" Project="false" />
-  </Project>
   <Project Path="PowerToysSetupCustomActionsVNext/PowerToysSetupCustomActionsVNext.vcxproj" Id="b3a354b0-1e54-4b55-a962-fb5af9330c19">
     <Build Solution="Debug|ARM64" Project="false" />
   </Project>

installer/PowerToysSetupVNext/DesktopGrass.wxs

@@ -0,0 +1,25 @@
+<Wix xmlns="http://wixtoolset.org/schemas/v4/wxs">
+
+  <?include $(sys.CURRENTDIR)\Common.wxi?>
+
+  <Fragment>
+    <!--
+      DesktopGrass ships a single statically-linked native executable
+      (DesktopGrass.Native.exe, /MT CRT, no external runtime dependencies). It is
+      emitted to the root build output and harvested automatically by the root
+      sweep in generateAllFileComponents.ps1 into BaseApplicationsComponentGroup.
+
+      This component group only carries the module's uninstall marker so the
+      feature can be referenced explicitly from Product.wxs, matching the
+      per-module convention used by Awake/Hosts/etc.
+    -->
+    <ComponentGroup Id="DesktopGrassComponentGroup">
+      <Component Id="RemoveDesktopGrassRegistry" Guid="42C1C544-8FD8-422A-85A2-139D99D38B52" Directory="INSTALLFOLDER">
+        <RegistryKey Root="$(var.RegistryScope)" Key="Software\Classes\powertoys\components">
+          <RegistryValue Type="string" Name="RemoveDesktopGrassRegistry" Value="" KeyPath="yes" />
+        </RegistryKey>
+      </Component>
+    </ComponentGroup>
+
+  </Fragment>
+</Wix>

installer/PowerToysSetupVNext/PowerToysInstallerVNext.wixproj

@@ -115,6 +115,7 @@ call powershell.exe -NonInteractive -executionpolicy Unrestricted -File $(MSBuil
     <Compile Include="BaseApplications.wxs" />
     <Compile Include="CmdPal.wxs" />
     <Compile Include="ColorPicker.wxs" />
+    <Compile Include="DesktopGrass.wxs" />
     <Compile Include="EnvironmentVariables.wxs" />
     <Compile Include="FileExplorerPreview.wxs" />
     <Compile Include="FileLocksmith.wxs" />

installer/PowerToysSetupVNext/Product.wxs

@@ -45,6 +45,7 @@
       <ComponentGroupRef Id="WinUI3ApplicationsComponentGroup" />
       <ComponentGroupRef Id="AwakeComponentGroup" />
       <ComponentGroupRef Id="ColorPickerComponentGroup" />
+      <ComponentGroupRef Id="DesktopGrassComponentGroup" />
       <ComponentGroupRef Id="FileExplorerPreviewComponentGroup" />
       <ComponentGroupRef Id="FileLocksmithComponentGroup" />
       <ComponentGroupRef Id="HostsComponentGroup" />

installer/PowerToysSetupVNext/ShortcutGuide.wxs

@@ -2,26 +2,39 @@
 
   <?include $(sys.CURRENTDIR)\Common.wxi?>
 
-  <?define ShortcutGuideSvgFiles=?>
-  <?define ShortcutGuideSvgFilesPath=$(var.BinDir)\Assets\ShortcutGuide\?>
+  <?define ShortcutGuideAssetsFiles=?>
+  <?define ShortcutGuideAssetsFilesPath=$(var.BinDir)WinUI3Apps\Assets\ShortcutGuide\?>
+  <?define ShortcutGuideManifestsFiles=?>
+  <?define ShortcutGuideManifestsFilesPath=$(var.BinDir)WinUI3Apps\Assets\ShortcutGuide\Manifests\?>
 
   <Fragment>
-    <!-- Shortcut guide files -->
-    <DirectoryRef Id="BaseApplicationsAssetsFolder">
-      <Directory Id="ShortcutGuideSvgsInstallFolder" Name="ShortcutGuide" />
+    <DirectoryRef Id="WinUI3AppsAssetsFolder">
+      <Directory Id="ShortcutGuideAssetsFolder" Name="ShortcutGuide">
+        <Directory Id="ShortcutGuideManifestsFolder" Name="Manifests" />
+      </Directory>
     </DirectoryRef>
-    <DirectoryRef Id="ShortcutGuideSvgsInstallFolder" FileSource="$(var.ShortcutGuideSvgFilesPath)">
+    <DirectoryRef Id="ShortcutGuideAssetsFolder" FileSource="$(var.ShortcutGuideAssetsFilesPath)">
     <!-- Generated by generateFileComponents.ps1 -->
-    <!--ShortcutGuideSvgFiles_Component_Def-->
+    <!--ShortcutGuideAssetsFiles_Component_Def-->
+    </DirectoryRef>
+    <DirectoryRef Id="ShortcutGuideManifestsFolder" FileSource="$(var.ShortcutGuideManifestsFilesPath)">
+    <!-- Generated by generateFileComponents.ps1 -->
+    <!--ShortcutGuideManifestsFiles_Component_Def-->
     </DirectoryRef>
 
     <!-- Shortcut guide -->
-    <ComponentGroup Id="ShortcutGuideComponentGroup">
-      <Component Id="RemoveShortcutGuideFolder" Guid="AD1ABC55-B593-4A60-A86A-BA8C0ED493A5" Directory="ShortcutGuideSvgsInstallFolder">
+    <ComponentGroup Id="ShortcutGuideComponentGroup" >
+      <Component Id="RemoveShortcutGuideFolder" Guid="AD1ABC55-B593-4A60-A86A-BA8C0ED493A5" Directory="ShortcutGuideAssetsFolder" >
         <RegistryKey Root="$(var.RegistryScope)" Key="Software\Classes\powertoys\components">
-          <RegistryValue Type="string" Name="RemoveShortcutGuideFolder" Value="" KeyPath="yes" />
+          <RegistryValue Type="string" Name="RemoveShortcutGuideFolder" Value="" KeyPath="yes"/>
         </RegistryKey>
-        <RemoveFolder Id="RemoveFolderShortcutGuideSvgsInstallFolder" Directory="ShortcutGuideSvgsInstallFolder" On="uninstall" />
+        <RemoveFolder Id="RemoveFolderShortcutGuideAssetsInstallFolder" Directory="ShortcutGuideAssetsFolder" On="uninstall"/>
+      </Component>
+      <Component Id="RemoveShortcutGuideManifestsFolder" Guid="F47E2C3A-8D91-4B6F-A2E5-9C8D7F6A1B3E" Directory="ShortcutGuideManifestsFolder" >
+        <RegistryKey Root="$(var.RegistryScope)" Key="Software\Classes\powertoys\components">
+          <RegistryValue Type="string" Name="RemoveShortcutGuideManifestsFolder" Value="" KeyPath="yes"/>
+        </RegistryKey>
+        <RemoveFolder Id="RemoveFolderShortcutGuideManifestsInstallFolder" Directory="ShortcutGuideManifestsFolder" On="uninstall"/>
       </Component>
     </ComponentGroup>
 

installer/PowerToysSetupVNext/generateAllFileComponents.ps1

@@ -28,7 +28,7 @@ Function Generate-FileList() {
 
     $fileExclusionList = @("*.pdb", "*.lastcodeanalysissucceeded", "createdump.exe", "powertoys.exe")
 
-    $fileInclusionList = @("*.dll", "*.exe", "*.json", "*.msix", "*.png", "*.gif", "*.ico", "*.cur", "*.svg", "index.html", "reg.js", "gitignore.js", "srt.js", "monacoSpecialLanguages.js", "customTokenThemeRules.js", "*.pri")
+    $fileInclusionList = @("*.dll", "*.exe", "*.json", "*.msix", "*.png", "*.gif", "*.ico", "*.cur", "*.svg", "index.html", "reg.js", "gitignore.js", "srt.js", "monacoSpecialLanguages.js", "customTokenThemeRules.js", "*.pri", "*.yml")
 
     # MFC DLLs leak into the output via WindowsAppSDKSelfContained but no PowerToys binary imports them.
     # Verified with dumpbin /dependents across all 2176 binaries — zero consumers.
@@ -112,6 +112,8 @@ Function Generate-FileComponents() {
 
     foreach ($file in $fileList) {
         $fileTmp = $file -replace "-", "_"
+        $fileTmp = $fileTmp -replace "[^A-Za-z0-9_.]", "_"
+        if ($fileTmp -match "^[^A-Za-z_]") { $fileTmp = "_$fileTmp" }
         $componentDefs +=
     @"
               <File Id="$($fileListName)_File_$($fileTmp)" Source="`$(var.$($fileListName)Path)\$($file)" />`r`n
@@ -397,8 +399,24 @@ Generate-FileComponents -fileListName "ValueGeneratorImagesCmpFiles" -wxsFilePat
 ## Plugins
 
 #ShortcutGuide
-Generate-FileList -fileDepsJson "" -fileListName ShortcutGuideSvgFiles -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs -depsPath "$PSScriptRoot..\..\..\$platform\Release\Assets\ShortcutGuide\"
-Generate-FileComponents -fileListName "ShortcutGuideSvgFiles" -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs
+# Ensure manifest yml files are in the build output (the Build target's CopyToOutputDirectory
+# may not run reliably under -graph mode in solution builds).
+$sgManifestsSrc = "$PSScriptRoot..\..\..\src\modules\ShortcutGuide\ShortcutGuide.Ui\Assets\ShortcutGuide\Manifests"
+$sgManifestsDst = "$PSScriptRoot..\..\..\$platform\Release\WinUI3Apps\Assets\ShortcutGuide\Manifests"
+Write-Host "ShortcutGuide manifests: src=$sgManifestsSrc exists=$(Test-Path $sgManifestsSrc)"
+Write-Host "ShortcutGuide manifests: dst=$sgManifestsDst exists=$(Test-Path $sgManifestsDst)"
+if (Test-Path $sgManifestsSrc) {
+    New-Item -Path $sgManifestsDst -ItemType Directory -Force | Out-Null
+    Copy-Item "$sgManifestsSrc\*.yml" -Destination $sgManifestsDst -Force
+    $copied = (Get-ChildItem "$sgManifestsDst\*.yml" -ErrorAction SilentlyContinue).Count
+    Write-Host "ShortcutGuide manifests: copied $copied yml files to build output"
+} else {
+    Write-Host "WARNING: ShortcutGuide manifest source not found at $sgManifestsSrc"
+}
+Generate-FileList -fileDepsJson "" -fileListName ShortcutGuideAssetsFiles -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs -depsPath "$PSScriptRoot..\..\..\$platform\Release\WinUI3Apps\Assets\ShortcutGuide\"
+Generate-FileComponents -fileListName "ShortcutGuideAssetsFiles" -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs
+Generate-FileList -fileDepsJson "" -fileListName ShortcutGuideManifestsFiles -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs -depsPath "$PSScriptRoot..\..\..\$platform\Release\WinUI3Apps\Assets\ShortcutGuide\Manifests\"
+Generate-FileComponents -fileListName "ShortcutGuideManifestsFiles" -wxsFilePath $PSScriptRoot\ShortcutGuide.wxs
 
 #Settings
 Generate-FileList -fileDepsJson "" -fileListName SettingsV2AssetsFiles -wxsFilePath $PSScriptRoot\Settings.wxs -depsPath "$PSScriptRoot..\..\..\$platform\Release\WinUI3Apps\Assets\Settings\"

src/ActionRunner/actionRunner.vcxproj

@@ -14,7 +14,6 @@
   <PropertyGroup Label="Configuration">
     
   </PropertyGroup>
-  <Import Project="$(RepoRoot)deps\expected.props" />
   <PropertyGroup>
     <ConfigurationType>Application</ConfigurationType>
   </PropertyGroup>

src/Update/PowerToys.Update.cpp

@@ -14,6 +14,8 @@
 #include <common/updating/updating.h>
 #include <common/updating/updateState.h>
 #include <common/updating/installer.h>
+#include <common/updating/configBackup.h>
+#include <common/updating/updateLifecycle.h>
 
 #include <common/utils/elevation.h>
 #include <common/utils/HttpClient.h>
@@ -21,6 +23,8 @@
 #include <common/utils/resources.h>
 #include <common/utils/timeutil.h>
 
+#include <wil/resource.h>
+
 #include <common/SettingsAPI/settings_helpers.h>
 
 #include <common/logger/logger.h>
@@ -36,17 +40,59 @@ using namespace cmdArg;
 
 namespace fs = std::filesystem;
 
+void CleanupStaleTempUpdaters()
+{
+    // Remove orphaned PowerToys.Update.*.exe files from previous runs
+    try
+    {
+        std::error_code ec;
+        const auto tempDir = fs::temp_directory_path();
+        for (const auto& entry : fs::directory_iterator(tempDir, ec))
+        {
+            if (ec)
+            {
+                break;
+            }
+
+            if (!entry.is_regular_file())
+            {
+                continue;
+            }
+
+            const auto filename = entry.path().filename().wstring();
+            if (filename.starts_with(L"PowerToys.Update.") && filename.ends_with(L".exe"))
+            {
+                // Skip our own file (current PID)
+                const auto ownFilename = L"PowerToys.Update." + std::to_wstring(GetCurrentProcessId()) + L".exe";
+                if (filename == ownFilename)
+                {
+                    continue;
+                }
+
+                fs::remove(entry.path(), ec);
+                // Failure to delete is expected if another updater is still running
+            }
+        }
+    }
+    catch (...)
+    {
+        // Best-effort cleanup; don't block the update
+    }
+}
+
 std::optional<fs::path> CopySelfToTempDir()
 {
+    CleanupStaleTempUpdaters();
+
     std::error_code error;
-    auto dst_path = fs::temp_directory_path() / "PowerToys.Update.exe";
+    auto dst_path = fs::temp_directory_path() / (L"PowerToys.Update." + std::to_wstring(GetCurrentProcessId()) + L".exe");
     fs::copy_file(get_module_filename(), dst_path, fs::copy_options::overwrite_existing, error);
     if (error)
     {
         return std::nullopt;
     }
 
-    return std::move(dst_path);
+    return dst_path;
 }
 
 std::optional<fs::path> ObtainInstaller(bool& isUpToDate)
@@ -57,34 +103,9 @@ std::optional<fs::path> ObtainInstaller(bool& isUpToDate)
 
     auto state = UpdateState::read();
 
-    const auto new_version_info = std::move(get_github_version_info_async()).get();
-    if (std::holds_alternative<version_up_to_date>(*new_version_info))
-    {
-        isUpToDate = true;
-        Logger::error("Invoked with -update_now argument, but no update was available");
-        return std::nullopt;
-    }
-
-    if (state.state == UpdateState::readyToDownload || state.state == UpdateState::errorDownloading)
-    {
-        if (!new_version_info)
-        {
-            Logger::error(L"Couldn't obtain github version info: {}", new_version_info.error());
-            return std::nullopt;
-        }
-
-        // Cleanup old updates before downloading the latest
-        updating::cleanup_updates();
-
-        auto downloaded_installer = std::move(download_new_version_async(std::get<new_version_download_info>(*new_version_info))).get();
-        if (!downloaded_installer)
-        {
-            Logger::error("Couldn't download new installer");
-        }
-
-        return downloaded_installer;
-    }
-    else if (state.state == UpdateState::readyToInstall)
+    // Handle readyToInstall first — the installer is already on disk,
+    // so we don't need a GitHub API call (which may fail if offline).
+    if (state.state == UpdateState::readyToInstall)
     {
         fs::path installer{ get_pending_updates_path() / state.downloadedInstallerFilename };
         if (fs::is_regular_file(installer))
@@ -97,12 +118,44 @@ std::optional<fs::path> ObtainInstaller(bool& isUpToDate)
             return std::nullopt;
         }
     }
-    else if (state.state == UpdateState::upToDate)
+
+    if (state.state == UpdateState::upToDate)
     {
         isUpToDate = true;
         return std::nullopt;
     }
 
+    const auto new_version_info = std::move(get_github_version_info_async()).get();
+
+    // Check for error BEFORE dereferencing — the old code crashed here
+    // when GitHub API was unreachable (new_version_info held an error string).
+    if (!new_version_info)
+    {
+        Logger::error(L"Couldn't obtain github version info: {}", new_version_info.error());
+        return std::nullopt;
+    }
+
+    if (std::holds_alternative<version_up_to_date>(*new_version_info))
+    {
+        isUpToDate = true;
+        Logger::error("Invoked with -update_now argument, but no update was available");
+        return std::nullopt;
+    }
+
+    if (state.state == UpdateState::readyToDownload || state.state == UpdateState::errorDownloading)
+    {
+        // Cleanup old updates before downloading the latest
+        updating::cleanup_updates();
+
+        auto downloaded_installer = std::move(download_new_version_async(std::get<new_version_download_info>(*new_version_info))).get();
+        if (!downloaded_installer)
+        {
+            Logger::error("Couldn't download new installer");
+        }
+
+        return downloaded_installer;
+    }
+
     Logger::error("Invoked with -update_now argument, but update state was invalid");
     return std::nullopt;
 }
@@ -116,13 +169,32 @@ bool InstallNewVersionStage1(fs::path installer)
 
         if (pt_main_window != nullptr)
         {
-            SendMessageW(pt_main_window, WM_CLOSE, 0, 0);
+            // Get the process that owns the tray window so we can wait for it to exit
+            DWORD ptProcessId = 0;
+            GetWindowThreadProcessId(pt_main_window, &ptProcessId);
+
+            // Use SendMessageTimeoutW to avoid blocking indefinitely if the
+            // tray window thread is hung or unresponsive.
+            DWORD_PTR result = 0;
+            SendMessageTimeoutW(pt_main_window, WM_CLOSE, 0, 0, SMTO_ABORTIFHUNG, 5000, &result);
+
+            // Wait for PT to actually exit before launching installer.
+            // Without this, the installer may find PT files locked.
+            if (ptProcessId != 0)
+            {
+                wil::unique_handle ptProcess{ OpenProcess(SYNCHRONIZE, FALSE, ptProcessId) };
+                if (ptProcess)
+                {
+                    WaitForSingleObject(ptProcess.get(), 10000); // 10 second timeout
+                }
+            }
         }
 
-        std::wstring arguments{ UPDATE_NOW_LAUNCH_STAGE2 };
-        arguments += L" \"";
-        arguments += installer.c_str();
-        arguments += L"\"";
+        // Pass the install directory so Stage 2 can relaunch PowerToys after install
+        const std::wstring installDir = get_module_folderpath();
+
+        std::wstring arguments = updating::BuildStage2Arguments(
+            UPDATE_NOW_LAUNCH_STAGE2, installer, fs::path(installDir));
         SHELLEXECUTEINFOW sei{ sizeof(sei) };
         sei.fMask = { SEE_MASK_FLAG_NO_UI | SEE_MASK_NOASYNC };
         sei.lpFile = copy_in_temp->c_str();
@@ -190,9 +262,16 @@ int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
     LPWSTR* args = CommandLineToArgvW(GetCommandLineW(), &nArgs);
     if (!args || nArgs < 2)
     {
+        if (args)
+        {
+            LocalFree(args);
+        }
         return 1;
     }
 
+    // D3 fix: ensure args is freed on all exit paths
+    auto freeArgs = wil::scope_exit([&] { LocalFree(args); });
+
     std::wstring_view action{ args[1] };
 
     std::filesystem::path logFilePath(PTSettingsHelper::get_root_save_folder_location());
@@ -201,6 +280,11 @@ int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
 
     if (action == UPDATE_NOW_LAUNCH_STAGE1)
     {
+        // Backup config files before the update to protect against corruption
+        Logger::info("Backing up config files before update");
+        auto backupResult = updating::BackupConfigFiles(fs::path(PTSettingsHelper::get_root_save_folder_location()));
+        Logger::info("Config backup complete: {} files backed up, {} errors", backupResult.filesBackedUp, backupResult.errors);
+
         bool isUpToDate = false;
         auto installerPath = ObtainInstaller(isUpToDate);
         bool failed = !installerPath.has_value();
@@ -217,6 +301,12 @@ int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
     }
     else if (action == UPDATE_NOW_LAUNCH_STAGE2)
     {
+        if (nArgs < 3)
+        {
+            Logger::error("Stage 2 invoked without installer path argument");
+            return 1;
+        }
+
         using namespace std::string_view_literals;
         const bool failed = !InstallNewVersionStage2(args[2]);
         if (failed)
@@ -227,6 +317,39 @@ int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
                 state.state = UpdateState::errorDownloading;
             });
         }
+
+        // Always check for corrupted configs after Stage 2, regardless
+        // of install success/failure. A failed install may still corrupt configs.
+        Logger::info("Checking for corrupted config files after update");
+        auto restoreResult = updating::RestoreCorruptedConfigs(fs::path(PTSettingsHelper::get_root_save_folder_location()));
+        Logger::info("Config restore check complete: {}/{} files restored, {} errors",
+                     restoreResult.filesRestored, restoreResult.filesChecked, restoreResult.errors);
+
+        if (!failed)
+        {
+            // Relaunch PowerToys from the install directory
+            if (updating::CanRelaunchAfterUpdate(nArgs))
+            {
+                std::wstring ptExePath = updating::BuildPowerToysExePath(args[3]);
+
+                Logger::info(L"Relaunching PowerToys after update: {}", ptExePath);
+
+                SHELLEXECUTEINFOW sei{ sizeof(sei) };
+                sei.fMask = { SEE_MASK_FLAG_NO_UI | SEE_MASK_NOASYNC };
+                sei.lpFile = ptExePath.c_str();
+                sei.nShow = SW_SHOWNORMAL;
+                sei.lpParameters = UPDATE_REPORT_SUCCESS;
+
+                if (!ShellExecuteExW(&sei))
+                {
+                    Logger::error(L"Failed to relaunch PowerToys after update");
+                }
+            }
+            else
+            {
+                Logger::warn("Install directory not provided to Stage 2 - cannot relaunch PowerToys");
+            }
+        }
         return failed;
     }
 

src/Update/PowerToys.Update.vcxproj

@@ -14,7 +14,6 @@
   <PropertyGroup Label="Configuration">
     
   </PropertyGroup>
-  <Import Project="$(RepoRoot)deps\expected.props" />
   <PropertyGroup>
     <ConfigurationType>Application</ConfigurationType>
   </PropertyGroup>

src/common/ManagedCommon/IdRecoveryHelper.cs

@@ -2,43 +2,35 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-using System;
 using System.Collections.Generic;
-using System.Collections.ObjectModel;
-using System.Linq;
-using System.Text;
-using System.Threading.Tasks;
 
 namespace ManagedCommon
 {
     public static class IdRecoveryHelper
     {
         /// <summary>
-        /// Fixes invalid IDs in the given list by assigning unique values.
-        /// It ensures that all IDs are non-empty and unique, correcting any duplicates or empty IDs.
+        /// Ensures that all items in the provided list have unique IDs. Duplicate IDs are replaced
+        /// with the next available unique ID.
         /// </summary>
-        /// <param name="items">The list of items that may contain invalid IDs.</param>
+        /// <param name="items">The list of items that may contain duplicate IDs.</param>
         public static void RecoverInvalidIds<T>(IEnumerable<T> items)
             where T : class, IHasId
         {
-            var idSet = new HashSet<int>();
-            int newId = 0;
-            var sortedItems = items.OrderBy(i => i.Id).ToList(); // Sort items by ID for consistent processing
+            var seenIds = new HashSet<int>();
+            int nextAvailableId = 0;
 
-            // Iterate through the list and fix invalid IDs
-            foreach (var item in sortedItems)
+            foreach (var item in items)
             {
-                // If the ID is invalid or already exists in the set (duplicate), assign a new unique ID
-                if (!idSet.Add(item.Id))
+                // If this ID is already used, assign a new unique ID.
+                if (!seenIds.Add(item.Id))
                 {
-                    // Find the next available unique ID
-                    while (idSet.Contains(newId))
+                    // Find the next unused ID.
+                    while (!seenIds.Add(nextAvailableId))
                     {
-                        newId++;
+                        nextAvailableId++;
                     }
 
-                    item.Id = newId;
-                    idSet.Add(newId); // Add the newly assigned ID to the set
+                    item.Id = nextAvailableId;
                 }
             }
         }

src/common/UnitTests-CommonUtils/UnitTests-CommonUtils.vcxproj

@@ -27,7 +27,7 @@
   <PropertyGroup Label="UserMacros" />
   <ItemDefinitionGroup>
     <ClCompile>
-      <AdditionalIncludeDirectories>..\;..\utils;..\Telemetry;..\..\;..\..\..\deps\;..\..\..\deps\spdlog\include;..\..\..\packages\Microsoft.Windows.ImplementationLibrary.1.0.260126.7\include;$(VCInstallDir)UnitTest\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
+      <AdditionalIncludeDirectories>..\;..\utils;..\Telemetry;..\..\;..\..\..\deps\;..\..\..\packages\Microsoft.Windows.ImplementationLibrary.1.0.260126.7\include;$(VCInstallDir)UnitTest\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
       <LanguageStandard>stdcpp23</LanguageStandard>
       <PreprocessorDefinitions>SPDLOG_WCHAR_TO_UTF8_SUPPORT;SPDLOG_HEADER_ONLY;%(PreprocessorDefinitions)</PreprocessorDefinitions>
     </ClCompile>

src/common/interop/Constants.cpp

@@ -259,6 +259,10 @@ namespace winrt::PowerToys::Interop::implementation
     {
         return CommonSharedConstants::TERMINATE_POWER_DISPLAY_EVENT;
     }
+    hstring Constants::AutoDisablePowerDisplayEvent()
+    {
+        return CommonSharedConstants::POWER_DISPLAY_AUTO_DISABLE_EVENT;
+    }
     hstring Constants::RefreshPowerDisplayMonitorsEvent()
     {
         return CommonSharedConstants::REFRESH_POWER_DISPLAY_MONITORS_EVENT;

src/common/interop/Constants.h

@@ -68,6 +68,7 @@ namespace winrt::PowerToys::Interop::implementation
         static hstring ShowCmdPalEvent();
         static hstring TogglePowerDisplayEvent();
         static hstring TerminatePowerDisplayEvent();
+        static hstring AutoDisablePowerDisplayEvent();
         static hstring RefreshPowerDisplayMonitorsEvent();
         static hstring SettingsUpdatedPowerDisplayEvent();
         static hstring PowerDisplaySendSettingsTelemetryEvent();

src/common/interop/Constants.idl

@@ -65,6 +65,7 @@ namespace PowerToys
             static String ShowCmdPalEvent();
             static String TogglePowerDisplayEvent();
             static String TerminatePowerDisplayEvent();
+            static String AutoDisablePowerDisplayEvent();
             static String RefreshPowerDisplayMonitorsEvent();
             static String SettingsUpdatedPowerDisplayEvent();
             static String PowerDisplaySendSettingsTelemetryEvent();

src/common/interop/PowerToys.Interop.vcxproj

@@ -41,7 +41,6 @@
   </PropertyGroup>
   <PropertyGroup Label="Configuration">
     <ConfigurationType>DynamicLibrary</ConfigurationType>
-    
     <CharacterSet>Unicode</CharacterSet>
     <GenerateManifest>false</GenerateManifest>
   </PropertyGroup>
@@ -100,6 +99,7 @@
     <ClInclude Include="Constants.h">
       <DependentUpon>KeyboardListener.idl</DependentUpon>
     </ClInclude>
+    <ClInclude Include="excluded_app.h" />
     <ClInclude Include="HotkeyManager.h">
       <DependentUpon>HotkeyManager.idl</DependentUpon>
     </ClInclude>
@@ -114,6 +114,7 @@
     <ClInclude Include="pch.h" />
     <ClInclude Include="resource.h" />
     <ClInclude Include="shared_constants.h" />
+    <ClInclude Include="tasklist_positions.h" />
     <ClInclude Include="TwoWayPipeMessageIPCManaged.h">
       <DependentUpon>TwoWayPipeMessageIPCManaged.idl</DependentUpon>
     </ClInclude>
@@ -127,6 +128,7 @@
     <ClCompile Include="Constants.cpp">
       <DependentUpon>KeyboardListener.idl</DependentUpon>
     </ClCompile>
+    <ClCompile Include="excluded_app.cpp" />
     <ClCompile Include="HotkeyManager.cpp">
       <DependentUpon>HotkeyManager.idl</DependentUpon>
     </ClCompile>
@@ -140,6 +142,7 @@
     <ClCompile Include="pch.cpp">
       <PrecompiledHeader>Create</PrecompiledHeader>
     </ClCompile>
+    <ClCompile Include="tasklist_positions.cpp" />
     <ClCompile Include="TwoWayPipeMessageIPCManaged.cpp">
       <DependentUpon>TwoWayPipeMessageIPCManaged.idl</DependentUpon>
     </ClCompile>
@@ -165,6 +168,9 @@
     <Midl Include="TwoWayPipeMessageIPCManaged.idl" />
   </ItemGroup>
   <ItemGroup>
+    <ProjectReference Include="..\SettingsAPI\SettingsAPI.vcxproj">
+      <Project>{6955446d-23f7-4023-9bb3-8657f904af99}</Project>
+    </ProjectReference>
     <ProjectReference Include="..\version\version.vcxproj">
       <Project>{cc6e41ac-8174-4e8a-8d22-85dd7f4851df}</Project>
     </ProjectReference>

src/common/interop/PowerToys.Interop.vcxproj.filters

@@ -54,6 +54,12 @@
     <ClInclude Include="Constants.h">
       <Filter>Header Files</Filter>
     </ClInclude>
+    <ClInclude Include="excluded_app.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
+    <ClInclude Include="tasklist_positions.h">
+      <Filter>Header Files</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="keyboard_layout.cpp">
@@ -83,6 +89,12 @@
     <ClCompile Include="Constants.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="excluded_app.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
+    <ClCompile Include="tasklist_positions.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ResourceCompile Include="interop.rc">

src/common/interop/excluded_app.cpp

@@ -0,0 +1,41 @@
+#include "pch.h"
+#include "excluded_app.h"
+#include <../utils/string_utils.h>
+
+extern "C"
+{
+    __declspec(dllexport) bool IsCurrentWindowExcludedFromShortcutGuide()
+    {
+        PowerToysSettings::PowerToyValues settings = PowerToysSettings::PowerToyValues::load_from_settings_file(L"Shortcut Guide");
+        auto settingsObject = settings.get_raw_json();
+        std::wstring apps = settingsObject.GetNamedObject(L"properties").GetNamedObject(L"disabled_apps").GetNamedString(L"value").c_str();
+        auto excludedUppercase = apps;
+        CharUpperBuffW(excludedUppercase.data(), static_cast<DWORD>(excludedUppercase.length()));
+        std::wstring_view view(excludedUppercase);
+        view = left_trim<wchar_t>(trim<wchar_t>(view));
+
+        m_excludedApps.clear();
+
+        while (!view.empty())
+        {
+            auto pos = (std::min)(view.find_first_of(L"\r\n"), view.length());
+            m_excludedApps.emplace_back(view.substr(0, pos));
+            view.remove_prefix(pos);
+            view = left_trim<wchar_t>(trim<wchar_t>(view));
+        }
+
+        if (m_excludedApps.empty())
+        {
+            return false;
+        }
+
+        if (HWND foregroundApp{ GetForegroundWindow() })
+        {
+            auto processPath = get_process_path(foregroundApp);
+            CharUpperBuffW(processPath.data(), static_cast<DWORD>(processPath.length()));
+
+            return check_excluded_app(foregroundApp, processPath, m_excludedApps);
+        }
+        return false;
+    }
+}

src/common/interop/excluded_app.h

@@ -0,0 +1,7 @@
+#pragma once
+
+extern "C"
+{
+    std::vector<std::wstring> m_excludedApps;
+    __declspec(dllexport) bool IsCurrentWindowExcludedFromShortcutGuide();
+}

src/common/interop/pch.h

@@ -12,3 +12,29 @@
 #include <winrt/Windows.Foundation.Collections.h>
 #include <Windows.h>
 #include <Endpointvolume.h>
+#include <vector>
+#include <UIAutomation.h>
+#include <dxgi1_3.h>
+#include <d3d11_2.h>
+#include <d2d1_3.h>
+#include <d2d1_3helper.h>
+#include <d2d1helper.h>
+#include <dwrite.h>
+#include <dcomp.h>
+#include <dwmapi.h>
+#include <Shobjidl.h>
+#include <Shlwapi.h>
+#include <string>
+#include <algorithm>
+#include <chrono>
+#include <mutex>
+#include <thread>
+#include <functional>
+#include <condition_variable>
+#include <stdexcept>
+#include <tuple>
+#include <unordered_set>
+#include <filesystem>
+#include <common/utils/excluded_apps.h>
+#include <common/utils/process_path.h>
+#include <../SettingsAPI/settings_objects.h>

src/common/interop/shared_constants.h

@@ -165,6 +165,7 @@ namespace CommonSharedConstants
     const wchar_t SETTINGS_UPDATED_POWER_DISPLAY_EVENT[] = L"Local\\PowerToysPowerDisplay-SettingsUpdatedEvent-2e4d6f8a-1c3b-5e7f-9a1d-4c6e8f0b2d3e";
     const wchar_t POWER_DISPLAY_SEND_SETTINGS_TELEMETRY_EVENT[] = L"Local\\PowerToysPowerDisplay-SettingsTelemetryEvent-8c4f2a1d-5e3b-7f9c-1a6d-3b8e5f2c9a7d";
     const wchar_t HOTKEY_UPDATED_POWER_DISPLAY_EVENT[] = L"Local\\PowerToysPowerDisplay-HotkeyUpdatedEvent-9d5f3a2b-7e1c-4b8a-6f3d-2a9e5c7b1d4f";
+    const wchar_t POWER_DISPLAY_AUTO_DISABLE_EVENT[] = L"Local\\PowerToysPowerDisplay-AutoDisableEvent-1a7bd9af-d2e0-4e57-8879-0e1c353994d0";
     const wchar_t RESCAN_POWER_DISPLAY_MONITORS_EVENT[] = L"Local\\PowerToysPowerDisplay-RescanMonitorsEvent-7f3e8c5a-1d4b-4a9e-bc6f-5d8a2b9e3c4f";
 
     // IPC Messages used in PowerDisplay (Named Pipe communication)

src/common/interop/tasklist_positions.cpp

@@ -0,0 +1,246 @@
+#include "pch.h"
+#include "tasklist_positions.h"
+
+// Tried my hardest adapting this to C#, but FindWindowW didn't work properly in C#. ~Noraa Junker
+
+static winrt::com_ptr<IUIAutomation> automation;
+static winrt::com_ptr<IUIAutomationElement> element;
+static winrt::com_ptr<IUIAutomationCondition> true_condition;
+
+extern "C"
+{
+    HWND GetTaskbarHwndForCursorMonitor(HMONITOR monitor)
+    {
+        POINT pt;
+        if (!GetCursorPos(&pt))
+            return nullptr;
+
+        // Find the primary taskbar
+        HWND primaryTaskbar = FindWindowW(L"Shell_TrayWnd", nullptr);
+        if (primaryTaskbar)
+        {
+            MONITORINFO mi = { sizeof(mi) };
+            if (GetWindowRect(primaryTaskbar, &mi.rcMonitor))
+            {
+                HMONITOR primaryMonitor = MonitorFromRect(&mi.rcMonitor, MONITOR_DEFAULTTONEAREST);
+                if (primaryMonitor == monitor)
+                    return primaryTaskbar;
+            }
+        }
+
+        // Find the secondary taskbar(s)
+        HWND secondaryTaskbar = nullptr;
+        while ((secondaryTaskbar = FindWindowExW(nullptr, secondaryTaskbar, L"Shell_SecondaryTrayWnd", nullptr)) != nullptr)
+        {
+            MONITORINFO mi = { sizeof(mi) };
+            RECT rc;
+            if (GetWindowRect(secondaryTaskbar, &rc))
+            {
+                HMONITOR taskbarMonitor = MonitorFromRect(&rc, MONITOR_DEFAULTTONEAREST);
+                if (monitor == taskbarMonitor)
+                    return secondaryTaskbar;
+            }
+        }
+
+        return nullptr;
+    }
+
+    void update(HMONITOR monitor)
+    {
+        // Get HWND of the tasklist for the monitor under the cursor
+        auto taskbar_hwnd = GetTaskbarHwndForCursorMonitor(monitor);
+        if (!taskbar_hwnd)
+            return;
+
+        wchar_t class_name[64] = {};
+        GetClassNameW(taskbar_hwnd, class_name, 64);
+
+        HWND tasklist_hwnd = nullptr;
+
+        if (wcscmp(class_name, L"Shell_TrayWnd") == 0)
+        {
+            // Primary taskbar structure
+            tasklist_hwnd = FindWindowExW(taskbar_hwnd, 0, L"ReBarWindow32", nullptr);
+            if (!tasklist_hwnd)
+                return;
+            tasklist_hwnd = FindWindowExW(tasklist_hwnd, 0, L"MSTaskSwWClass", nullptr);
+            if (!tasklist_hwnd)
+                return;
+            tasklist_hwnd = FindWindowExW(tasklist_hwnd, 0, L"MSTaskListWClass", nullptr);
+            if (!tasklist_hwnd)
+                return;
+        }
+        else if (wcscmp(class_name, L"Shell_SecondaryTrayWnd") == 0)
+        {
+            // Secondary taskbar structure
+            HWND worker_hwnd = FindWindowExW(taskbar_hwnd, 0, L"WorkerW", nullptr);
+            if (!worker_hwnd)
+                return;
+            tasklist_hwnd = FindWindowExW(worker_hwnd, 0, L"MSTaskListWClass", nullptr);
+            if (!tasklist_hwnd)
+                return;
+        }
+        else
+        {
+            // Unknown taskbar type
+            return;
+        }
+
+        if (!automation)
+        {
+            winrt::check_hresult(CoCreateInstance(CLSID_CUIAutomation,
+                                                  nullptr,
+                                                  CLSCTX_INPROC_SERVER,
+                                                  IID_IUIAutomation,
+                                                  automation.put_void()));
+            winrt::check_hresult(automation->CreateTrueCondition(true_condition.put()));
+        }
+        element = nullptr;
+        winrt::check_hresult(automation->ElementFromHandle(tasklist_hwnd, element.put()));
+    }
+
+    void update_new(HMONITOR monitor)
+    {
+        // Get HWND of the tasklist for the monitor under the cursor
+        auto taskbar_hwnd = GetTaskbarHwndForCursorMonitor(monitor);
+        if (!taskbar_hwnd)
+            return;
+
+        wchar_t class_name[64] = {};
+        GetClassNameW(taskbar_hwnd, class_name, 64);
+
+        HWND tasklist_hwnd = nullptr;
+
+        if (wcscmp(class_name, L"Shell_TrayWnd") == 0 || wcscmp(class_name, L"Shell_SecondaryTrayWnd") == 0)
+        {
+            // Primary taskbar structure
+            tasklist_hwnd = FindWindowExW(taskbar_hwnd, 0, L"Windows.UI.Composition.DesktopWindowContentBridge", nullptr);
+            if (!tasklist_hwnd)
+                return;
+            tasklist_hwnd = FindWindowExW(tasklist_hwnd, 0, L"Windows.UI.Input.InputSite.WindowClass", nullptr);
+            if (!tasklist_hwnd)
+                return;
+        }
+        else
+        {
+            // Unknown taskbar type
+            return;
+        }
+
+        if (!automation)
+        {
+            winrt::check_hresult(CoCreateInstance(CLSID_CUIAutomation,
+                                                  nullptr,
+                                                  CLSCTX_INPROC_SERVER,
+                                                  IID_IUIAutomation,
+                                                  automation.put_void()));
+            winrt::check_hresult(automation->CreateTrueCondition(true_condition.put()));
+        }
+
+        winrt::com_ptr<IUIAutomationElement> tempElement;
+        element = nullptr;
+        winrt::check_hresult(automation->ElementFromHandle(tasklist_hwnd, tempElement.put()));
+
+        winrt::check_hresult(
+            tempElement->FindFirst(TreeScope_Children, true_condition.get(), element.put()));
+    }
+
+    bool update_buttons(std::vector<TasklistButton>& buttons)
+    {
+        if (!automation || !element)
+        {
+            return false;
+        }
+        winrt::com_ptr<IUIAutomationElementArray> elements;
+        if (element->FindAll(TreeScope_Children, true_condition.get(), elements.put()) < 0)
+            return false;
+        if (!elements)
+            return false;
+        int count;
+        if (elements->get_Length(&count) < 0)
+            return false;
+        winrt::com_ptr<IUIAutomationElement> child;
+        std::vector<TasklistButton> found_buttons;
+        found_buttons.reserve(count);
+        for (int i = 0; i < count; ++i)
+        {
+            child = nullptr;
+            if (elements->GetElement(i, child.put()) < 0)
+                return false;
+            TasklistButton button = {};
+            if (VARIANT var_rect; child->GetCurrentPropertyValue(UIA_BoundingRectanglePropertyId, &var_rect) >= 0)
+            {
+                if (var_rect.vt == (VT_R8 | VT_ARRAY))
+                {
+                    LONG pos;
+                    double value;
+                    pos = 0;
+                    SafeArrayGetElement(var_rect.parray, &pos, &value);
+                    button.x = static_cast<long>(value);
+                    pos = 1;
+                    SafeArrayGetElement(var_rect.parray, &pos, &value);
+                    button.y = static_cast<long>(value);
+                    pos = 2;
+                    SafeArrayGetElement(var_rect.parray, &pos, &value);
+                    button.width = static_cast<long>(value);
+                    pos = 3;
+                    SafeArrayGetElement(var_rect.parray, &pos, &value);
+                    button.height = static_cast<long>(value);
+                }
+                VariantClear(&var_rect);
+            }
+            else
+            {
+                return false;
+            }
+            if (BSTR automation_id; child->get_CurrentAutomationId(&automation_id) >= 0)
+            {
+                wcsncpy_s(button.name, automation_id, _countof(button.name));
+                SysFreeString(automation_id);
+                if (wcsncmp(button.name, L"Appid:", wcslen(L"Appid:")) != 0)
+                {
+                    continue;
+                }
+            }
+            found_buttons.push_back(button);
+        }
+        // assign keynums
+        buttons.clear();
+        for (auto& button : found_buttons)
+        {
+            if (buttons.empty())
+            {
+                button.keynum = 1;
+                buttons.push_back(std::move(button));
+            }
+            else
+            {
+                if (button.x < buttons.back().x || button.y < buttons.back().y) // skip 2nd row
+                    break;
+                if (wcsncmp(button.name, buttons.back().name, _countof(button.name)) == 0)
+                    continue; // skip buttons from the same app
+                button.keynum = buttons.back().keynum + 1;
+                buttons.push_back(std::move(button));
+                if (buttons.back().keynum == 10)
+                    break; // no more than 10 buttons
+            }
+        }
+        return true;
+    }
+
+    __declspec(dllexport) TasklistButton* get_buttons(HMONITOR monitor, int* size)
+    {
+        update(monitor);
+        static std::vector<TasklistButton> buttons;
+        update_buttons(buttons);
+        *size = static_cast<int>(buttons.size());
+        if (*size == 0)
+        {
+            // After a certain Windows update, the old method stopped working, try the new one
+            update_new(monitor);
+            update_buttons(buttons);
+            *size = static_cast<int>(buttons.size());
+        }
+        return buttons.data();
+    }
+}

src/common/interop/tasklist_positions.h

@@ -0,0 +1,19 @@
+#pragma once
+
+struct TasklistButton
+{
+    wchar_t name[256];
+    int x;
+    int y;
+    int width;
+    int height;
+    int keynum;
+};
+
+extern "C"
+{
+    // Helper to get the taskbar HWND for the monitor under the cursor
+    HWND GetTaskbarHwndForCursorMonitor(HMONITOR monitor);
+    bool update_buttons(std::vector<TasklistButton>& buttons);
+    __declspec(dllexport) TasklistButton* get_buttons(HMONITOR monitor, int* size);
+}

src/common/logger/logger.vcxproj

@@ -70,9 +70,6 @@
     </ClCompile>
   </ItemGroup>
   <ItemGroup>
-    <ProjectReference Include="..\..\logging\logging.vcxproj">
-      <Project>{7e1e3f13-2bd6-3f75-a6a7-873a2b55c60f}</Project>
-    </ProjectReference>
     <ProjectReference Include="..\version\version.vcxproj">
       <Project>{cc6e41ac-8174-4e8a-8d22-85dd7f4851df}</Project>
     </ProjectReference>

src/common/updating/UnitTests/UpdatingTests.cpp

@@ -0,0 +1,679 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#include "pch.h"
+
+#include <algorithm>
+#include <filesystem>
+#include <fstream>
+#include <iterator>
+#include <string>
+#include <vector>
+
+#include <common/updating/configBackup.h>
+#include <common/updating/updateLifecycle.h>
+
+using namespace Microsoft::VisualStudio::CppUnitTestFramework;
+
+namespace fs = std::filesystem;
+
+namespace UpdatingUnitTests
+{
+    // Helper to create a temp directory for test isolation.
+    // Each instance gets a unique subdirectory to prevent test interference.
+    class TempDir
+    {
+    public:
+        TempDir()
+        {
+            wchar_t tempPath[MAX_PATH + 1];
+            GetTempPathW(MAX_PATH, tempPath);
+            static std::atomic<int> counter{0};
+            m_path = fs::path(tempPath) / (L"PowerToysUpdateTests_" + std::to_wstring(counter++));
+
+            // Ensure clean state
+            std::error_code ec;
+            fs::remove_all(m_path, ec);
+            fs::create_directories(m_path, ec);
+        }
+
+        ~TempDir()
+        {
+            std::error_code ec;
+            fs::remove_all(m_path, ec);
+        }
+
+        const fs::path& path() const { return m_path; }
+
+        // Write a file with the given content
+        void WriteFile(const fs::path& relativePath, const std::string& content)
+        {
+            auto fullPath = m_path / relativePath;
+            fs::create_directories(fullPath.parent_path());
+            std::ofstream file(fullPath, std::ios::binary);
+            file.write(content.data(), content.size());
+        }
+
+        // Write a file with raw bytes (including null bytes for corruption testing)
+        void WriteFileBytes(const fs::path& relativePath, const std::vector<char>& bytes)
+        {
+            auto fullPath = m_path / relativePath;
+            fs::create_directories(fullPath.parent_path());
+            std::ofstream file(fullPath, std::ios::binary);
+            file.write(bytes.data(), bytes.size());
+        }
+
+        // Read file content as string
+        std::string ReadFile(const fs::path& relativePath)
+        {
+            auto fullPath = m_path / relativePath;
+            std::ifstream file(fullPath, std::ios::binary);
+            return std::string(std::istreambuf_iterator<char>(file), std::istreambuf_iterator<char>());
+        }
+
+        bool FileExists(const fs::path& relativePath)
+        {
+            return fs::exists(m_path / relativePath);
+        }
+
+    private:
+        fs::path m_path;
+    };
+
+    TEST_CLASS(IsJsonFileCorruptedTests)
+    {
+    public:
+        // Tests IsJsonFileCorrupted: valid JSON with no null bytes returns false.
+        // Covers: configBackup.h IsJsonFileCorrupted — happy path, full file scan.
+        TEST_METHOD(CleanJsonFileIsNotCorrupted)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark","startup":true})");
+
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"settings.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: zero-length file returns false (empty is not corrupted).
+        // Covers: configBackup.h IsJsonFileCorrupted — file.read returns 0 bytes immediately.
+        TEST_METHOD(EmptyFileIsNotCorrupted)
+        {
+            TempDir dir;
+            dir.WriteFile(L"empty.json", "");
+
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"empty.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: file containing embedded null bytes returns true.
+        // Covers: configBackup.h IsJsonFileCorrupted — null byte detection within buffer.
+        TEST_METHOD(FileWithNullBytesIsCorrupted)
+        {
+            TempDir dir;
+            std::vector<char> corrupted = { '{', '"', 'a', '"', ':', '\0', '\0', '\0', '}' };
+            dir.WriteFileBytes(L"corrupted.json", corrupted);
+
+            Assert::IsTrue(updating::IsJsonFileCorrupted(dir.path() / L"corrupted.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: file entirely filled with 0x00 bytes returns true.
+        // Reproduces the exact bug from #46179 where installer zeroed out JSON files.
+        // Covers: configBackup.h IsJsonFileCorrupted — first byte is null.
+        TEST_METHOD(FileFilledWithNullBytesIsCorrupted)
+        {
+            TempDir dir;
+            std::vector<char> allNulls(1024, '\0');
+            dir.WriteFileBytes(L"workspaces.json", allNulls);
+
+            Assert::IsTrue(updating::IsJsonFileCorrupted(dir.path() / L"workspaces.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: path that does not exist returns false.
+        // Covers: configBackup.h IsJsonFileCorrupted — file.is_open() check.
+        TEST_METHOD(NonExistentFileIsNotCorrupted)
+        {
+            TempDir dir;
+
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"missing.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: file larger than the 4096-byte read chunk
+        // with no null bytes returns false.
+        // Covers: configBackup.h IsJsonFileCorrupted — multi-chunk while loop.
+        TEST_METHOD(LargeCleanFileIsNotCorrupted)
+        {
+            TempDir dir;
+            std::string largeContent(8192, 'x');
+            dir.WriteFile(L"large.json", largeContent);
+
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"large.json"));
+        }
+
+        // Tests IsJsonFileCorrupted: null byte placed after the first 4096-byte
+        // chunk boundary is still detected.
+        // Covers: configBackup.h IsJsonFileCorrupted — second chunk scan.
+        TEST_METHOD(NullByteAtEndOfLargeFileIsDetected)
+        {
+            TempDir dir;
+            std::string content(5000, 'x');
+            content[4999] = '\0';
+            std::vector<char> bytes(content.begin(), content.end());
+            dir.WriteFileBytes(L"sneaky.json", bytes);
+
+            Assert::IsTrue(updating::IsJsonFileCorrupted(dir.path() / L"sneaky.json"));
+        }
+    };
+
+    TEST_CLASS(BackupConfigFilesTests)
+    {
+    public:
+        // Tests BackupConfigFiles: root-level .json files are copied to ConfigBackup.
+        // Covers: configBackup.h BackupConfigFiles — root directory_iterator,
+        //         is_regular_file && extension == ".json" branch.
+        // Setup: Two root-level JSON files.
+        TEST_METHOD(BackupCopiesRootJsonFiles)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+            dir.WriteFile(L"UpdateState.json", R"({"state":0})");
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\settings.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\UpdateState.json"));
+            Assert::AreEqual(std::string(R"({"theme":"dark"})"), dir.ReadFile(L"ConfigBackup\\settings.json"));
+        }
+
+        // Tests BackupConfigFiles: .json files inside module subdirectories are
+        // copied to ConfigBackup/<module>/.
+        // Covers: configBackup.h BackupConfigFiles — is_directory branch,
+        //         module directory_iterator with extension filter.
+        // Setup: Root JSON + two module directories with JSON files.
+        TEST_METHOD(BackupCopiesModuleJsonFiles)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+            dir.WriteFile(L"FancyZones\\settings.json", R"({"zones":[]})");
+            dir.WriteFile(L"Workspaces\\workspaces.json", R"({"workspaces":[]})");
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\FancyZones\\settings.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\Workspaces\\workspaces.json"));
+            Assert::AreEqual(std::string(R"({"zones":[]})"),
+                dir.ReadFile(L"ConfigBackup\\FancyZones\\settings.json"));
+        }
+
+        // Tests BackupConfigFiles: non-.json files at root level are not copied.
+        // Covers: configBackup.h BackupConfigFiles — extension filter excludes .log.
+        // Setup: One JSON file + one .log file at root.
+        TEST_METHOD(BackupSkipsNonJsonFiles)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+            dir.WriteFile(L"debug.log", "log data");
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\settings.json"));
+            Assert::IsFalse(dir.FileExists(L"ConfigBackup\\debug.log"));
+        }
+
+        // Tests BackupConfigFiles: the "Updates" directory is explicitly skipped.
+        // Covers: configBackup.h BackupConfigFiles — dirName == L"Updates" continue.
+        // Setup: Root JSON + Updates directory containing a file.
+        TEST_METHOD(BackupSkipsUpdatesDirectory)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+            dir.WriteFile(L"Updates\\installer.exe", "fake exe");
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsFalse(dir.FileExists(L"ConfigBackup\\Updates"));
+        }
+
+        // Tests BackupConfigFiles: running backup twice overwrites the previous
+        // backup with current file content.
+        // Covers: configBackup.h BackupConfigFiles — fs::remove_all(backupDir) +
+        //         copy_options::overwrite_existing.
+        // Setup: Backup, modify original, backup again.
+        TEST_METHOD(BackupOverwritesPreviousBackup)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"version":1})");
+            updating::BackupConfigFiles(dir.path());
+
+            // Update the original
+            dir.WriteFile(L"settings.json", R"({"version":2})");
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::AreEqual(std::string(R"({"version":2})"), dir.ReadFile(L"ConfigBackup\\settings.json"));
+        }
+
+        // Tests BackupConfigFiles: non-.json files inside module subdirectories
+        // (e.g., FancyZones/zones.dat) should NOT be backed up.
+        // Covers: configBackup.h BackupConfigFiles — extension filter in module loop.
+        TEST_METHOD(BackupSkipsNonJsonFilesInModuleDirs)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({})");
+            dir.WriteFile(L"FancyZones\\settings.json", R"({"zones":[]})");
+            dir.WriteFile(L"FancyZones\\zones.dat", "binary data");
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\FancyZones\\settings.json"));
+            Assert::IsFalse(dir.FileExists(L"ConfigBackup\\FancyZones\\zones.dat"));
+        }
+
+        // Tests BackupConfigFiles: empty root directory with no files produces
+        // an empty ConfigBackup dir without errors.
+        // Covers: configBackup.h BackupConfigFiles — empty directory_iterator.
+        TEST_METHOD(BackupEmptyRootDirSucceeds)
+        {
+            TempDir dir;
+            // Root dir exists but has no files
+
+            updating::BackupConfigFiles(dir.path());
+
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup"));
+        }
+    };
+
+    TEST_CLASS(RestoreCorruptedConfigsTests)
+    {
+    public:
+        // Tests RestoreCorruptedConfigs: corrupted root-level JSON file is restored
+        // from the good backup copy.
+        // Covers: configBackup.h RestoreCorruptedConfigs — root file restore branch,
+        //         fs::exists + IsJsonFileCorrupted + backup integrity check.
+        // Setup: Good file -> backup -> corrupt original -> restore.
+        TEST_METHOD(RestoreFixesCorruptedRootFile)
+        {
+            TempDir dir;
+            const std::string goodContent = R"({"theme":"dark"})";
+            dir.WriteFile(L"settings.json", goodContent);
+
+            // Backup
+            updating::BackupConfigFiles(dir.path());
+
+            // Corrupt the original
+            std::vector<char> corrupted(goodContent.size(), '\0');
+            dir.WriteFileBytes(L"settings.json", corrupted);
+            Assert::IsTrue(updating::IsJsonFileCorrupted(dir.path() / L"settings.json"));
+
+            // Restore
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"settings.json"));
+            Assert::AreEqual(goodContent, dir.ReadFile(L"settings.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: corrupted module-level JSON file is restored
+        // from the good backup copy.
+        // Covers: configBackup.h RestoreCorruptedConfigs — module directory branch,
+        //         moduleBackupEntry restore with integrity check.
+        // Setup: Module file + root file -> backup -> corrupt module file -> restore.
+        TEST_METHOD(RestoreFixesCorruptedModuleFile)
+        {
+            TempDir dir;
+            const std::string goodContent = R"({"workspaces":[]})";
+            dir.WriteFile(L"Workspaces\\workspaces.json", goodContent);
+            dir.WriteFile(L"settings.json", R"({})");
+
+            updating::BackupConfigFiles(dir.path());
+
+            // Corrupt the module file
+            std::vector<char> corrupted(goodContent.size(), '\0');
+            dir.WriteFileBytes(L"Workspaces\\workspaces.json", corrupted);
+
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            Assert::AreEqual(goodContent, dir.ReadFile(L"Workspaces\\workspaces.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: clean (non-corrupted) files are NOT
+        // overwritten by backup — preserves user changes made after backup.
+        // Covers: configBackup.h RestoreCorruptedConfigs — IsJsonFileCorrupted
+        //         returns false, copy_file is skipped.
+        // Setup: File -> backup -> modify (but keep valid) -> restore.
+        TEST_METHOD(RestoreLeavesCleanFilesUntouched)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"version":1})");
+
+            updating::BackupConfigFiles(dir.path());
+
+            // Modify original (but keep it clean JSON)
+            dir.WriteFile(L"settings.json", R"({"version":2})");
+
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // Should NOT have been restored since it's not corrupted
+            Assert::AreEqual(std::string(R"({"version":2})"), dir.ReadFile(L"settings.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: when no ConfigBackup directory exists,
+        // restore silently does nothing (no crash, no data loss).
+        // Covers: configBackup.h RestoreCorruptedConfigs — !fs::exists(backupDir)
+        //         early return.
+        // Setup: File with no prior backup.
+        TEST_METHOD(RestoreHandlesMissingBackupDirectory)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+
+            // No backup was created - restore should silently do nothing
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            Assert::AreEqual(std::string(R"({"theme":"dark"})"), dir.ReadFile(L"settings.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: end-to-end scenario with multiple modules,
+        // some corrupted and some clean, verifying selective restore.
+        // Covers: configBackup.h RestoreCorruptedConfigs — both root and module
+        //         branches, selective restore based on corruption status.
+        // Setup: 4 modules -> backup -> corrupt 2 -> restore -> verify all 4.
+        TEST_METHOD(FullBackupAndRestoreRoundTrip)
+        {
+            TempDir dir;
+
+            // Set up a realistic config structure
+            dir.WriteFile(L"settings.json", R"({"startup":true,"theme":"dark"})");
+            dir.WriteFile(L"FancyZones\\settings.json", R"({"zones":[{"id":1}]})");
+            dir.WriteFile(L"Workspaces\\workspaces.json", R"({"workspaces":[{"name":"dev"}]})");
+            dir.WriteFile(L"KeyboardManager\\default.json", R"({"remaps":[]})");
+
+            // Backup
+            updating::BackupConfigFiles(dir.path());
+
+            // Corrupt some files (simulating #46179 scenario)
+            dir.WriteFileBytes(L"Workspaces\\workspaces.json", std::vector<char>(100, '\0'));
+            dir.WriteFileBytes(L"settings.json", std::vector<char>(50, '\0'));
+            // Leave FancyZones and KBM clean
+
+            // Restore
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // Corrupted files should be restored
+            Assert::AreEqual(std::string(R"({"startup":true,"theme":"dark"})"), dir.ReadFile(L"settings.json"));
+            Assert::AreEqual(std::string(R"({"workspaces":[{"name":"dev"}]})"), dir.ReadFile(L"Workspaces\\workspaces.json"));
+
+            // Clean files should be unchanged
+            Assert::AreEqual(std::string(R"({"zones":[{"id":1}]})"), dir.ReadFile(L"FancyZones\\settings.json"));
+            Assert::AreEqual(std::string(R"({"remaps":[]})"), dir.ReadFile(L"KeyboardManager\\default.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: when the original file has been deleted
+        // (not corrupted), restore should NOT recreate it from backup. The installer
+        // may have intentionally removed obsolete config files.
+        // Covers: configBackup.h RestoreCorruptedConfigs — fs::exists guard.
+        TEST_METHOD(RestoreSkipsDeletedOriginals)
+        {
+            TempDir dir;
+            dir.WriteFile(L"obsolete.json", R"({"old":true})");
+            updating::BackupConfigFiles(dir.path());
+
+            // Installer deletes the file
+            std::error_code ec;
+            fs::remove(dir.path() / L"obsolete.json", ec);
+
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // Should NOT be recreated
+            Assert::IsFalse(dir.FileExists(L"obsolete.json"));
+        }
+
+        // Tests RestoreCorruptedConfigs: when the backup file itself is corrupted
+        // (e.g., disk error during backup), restore should NOT copy corrupted
+        // backup over the original — that would make things worse.
+        // Covers: configBackup.h RestoreCorruptedConfigs — backup integrity check (B2 fix).
+        TEST_METHOD(RestoreSkipsCorruptedBackup)
+        {
+            TempDir dir;
+            dir.WriteFile(L"settings.json", R"({"theme":"dark"})");
+            updating::BackupConfigFiles(dir.path());
+
+            // Corrupt BOTH the original AND the backup
+            std::vector<char> nulls(50, '\0');
+            dir.WriteFileBytes(L"settings.json", nulls);
+            dir.WriteFileBytes(L"ConfigBackup\\settings.json", nulls);
+
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // Original should still be corrupted — we don't restore from bad backup
+            Assert::IsTrue(updating::IsJsonFileCorrupted(dir.path() / L"settings.json"));
+        }
+    };
+
+    // Simulates what actually happens during a PowerToys upgrade:
+    // 1. User has settings from normal use
+    // 2. Updater backs up before install (Stage 1)
+    // 3. Installer runs and corrupts some files (simulated)
+    // 4. Updater restores corrupted files (Stage 2)
+    // 5. PT relaunches and finds working configs
+    TEST_CLASS(UpgradeSimulationTests)
+    {
+    public:
+        // Tests full upgrade simulation: backup -> installer corrupts files -> restore.
+        // Verifies that corrupted files are restored and clean files are untouched.
+        // Covers: configBackup.h BackupConfigFiles + RestoreCorruptedConfigs —
+        //         end-to-end with 5 modules, 2 corrupted, 3 clean.
+        // Setup: Realistic config structure with multiple modules.
+        TEST_METHOD(SimulateUpgradeWithCorruption)
+        {
+            TempDir dir;
+
+            // === User's real config state before upgrade ===
+            dir.WriteFile(L"settings.json",
+                R"({"startup":true,"theme":"dark","run_elevated":false,"download_updates_automatically":true})");
+            dir.WriteFile(L"FancyZones\\settings.json",
+                R"({"zones":[{"id":1,"rect":{"x":0,"y":0,"w":960,"h":1080}}]})");
+            dir.WriteFile(L"Workspaces\\workspaces.json",
+                R"({"workspaces":[{"name":"dev","apps":["code","terminal"]}]})");
+            dir.WriteFile(L"KeyboardManager\\default.json",
+                R"({"remapKeys":{"inProcess":[{"original":"0x41","new":"0x42"}]}})");
+            dir.WriteFile(L"MouseWithoutBorders\\settings.json",
+                R"({"machineKey":"abc123","connectToAll":true})");
+
+            // Non-JSON files that should be left alone
+            dir.WriteFile(L"update.log", "2026-04-11 update started");
+
+            // === Stage 1: Backup before killing PT ===
+            updating::BackupConfigFiles(dir.path());
+
+            // Verify backup was created correctly
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\settings.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\FancyZones\\settings.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\Workspaces\\workspaces.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\KeyboardManager\\default.json"));
+            Assert::IsTrue(dir.FileExists(L"ConfigBackup\\MouseWithoutBorders\\settings.json"));
+            Assert::IsFalse(dir.FileExists(L"ConfigBackup\\update.log"));
+
+            // === Installer runs: some files get corrupted (the #46179 scenario) ===
+            // Workspaces JSON filled with null bytes
+            dir.WriteFileBytes(L"Workspaces\\workspaces.json", std::vector<char>(512, '\0'));
+            // Main settings partially corrupted (null bytes injected)
+            std::vector<char> partialCorrupt = { '{', '"', 's', '\0', '\0', '\0', '\0', '}' };
+            dir.WriteFileBytes(L"settings.json", partialCorrupt);
+
+            // FancyZones, KBM, and MWB survive the install fine
+            // (this is realistic - not all files get corrupted)
+
+            // === Stage 2: Restore after install completes ===
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // === Verify: PT relaunches and finds working configs ===
+
+            // Corrupted files should be restored from backup
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"settings.json"));
+            Assert::IsFalse(updating::IsJsonFileCorrupted(dir.path() / L"Workspaces\\workspaces.json"));
+            Assert::AreEqual(
+                std::string(R"({"startup":true,"theme":"dark","run_elevated":false,"download_updates_automatically":true})"),
+                dir.ReadFile(L"settings.json"));
+            Assert::AreEqual(
+                std::string(R"({"workspaces":[{"name":"dev","apps":["code","terminal"]}]})"),
+                dir.ReadFile(L"Workspaces\\workspaces.json"));
+
+            // Clean files should be untouched (not overwritten with backup)
+            Assert::AreEqual(
+                std::string(R"({"zones":[{"id":1,"rect":{"x":0,"y":0,"w":960,"h":1080}}]})"),
+                dir.ReadFile(L"FancyZones\\settings.json"));
+            Assert::AreEqual(
+                std::string(R"({"remapKeys":{"inProcess":[{"original":"0x41","new":"0x42"}]}})"),
+                dir.ReadFile(L"KeyboardManager\\default.json"));
+            Assert::AreEqual(
+                std::string(R"({"machineKey":"abc123","connectToAll":true})"),
+                dir.ReadFile(L"MouseWithoutBorders\\settings.json"));
+        }
+
+        // Tests upgrade from an old version that has fewer modules than the new version.
+        // Verifies that new module configs (created by the installer) are not touched
+        // by restore, while corrupted old configs are restored.
+        // Covers: configBackup.h RestoreCorruptedConfigs — module dir in root that
+        //         has no corresponding backup entry.
+        // Setup: Old version with 1 module -> backup -> new installer adds module -> corrupt old -> restore.
+        TEST_METHOD(SimulateUpgradeFromVeryOldVersion)
+        {
+            TempDir dir;
+
+            // Old version had fewer modules - only settings.json
+            dir.WriteFile(L"settings.json", R"({"theme":"dark","powertoys_version":"v0.60.0"})");
+
+            // Backup
+            updating::BackupConfigFiles(dir.path());
+
+            // New installer creates new module dirs that didn't exist before
+            dir.WriteFile(L"NewModule\\settings.json", R"({"enabled":true})");
+
+            // Old settings get corrupted during upgrade
+            dir.WriteFileBytes(L"settings.json", std::vector<char>(100, '\0'));
+
+            // Restore
+            updating::RestoreCorruptedConfigs(dir.path());
+
+            // Old settings restored
+            Assert::AreEqual(
+                std::string(R"({"theme":"dark","powertoys_version":"v0.60.0"})"),
+                dir.ReadFile(L"settings.json"));
+
+            // New module settings untouched (no backup existed for them)
+            Assert::AreEqual(
+                std::string(R"({"enabled":true})"),
+                dir.ReadFile(L"NewModule\\settings.json"));
+        }
+    };
+
+    // Tests for the update lifecycle: argument passing between Stage 1 and Stage 2,
+    // relaunch path construction, and the handoff that was broken in #42004/#43011/#44071.
+    TEST_CLASS(UpdateLifecycleTests)
+    {
+    public:
+        // Tests BuildStage2Arguments: output contains the stage 2 flag, installer path,
+        // and install directory — all three components needed for Stage 2.
+        // Covers: updateLifecycle.h BuildStage2Arguments — concatenation logic.
+        // Setup: Typical paths with spaces (Program Files).
+        TEST_METHOD(BuildStage2ArgumentsContainsInstallerAndInstallDir)
+        {
+            const auto args = updating::BuildStage2Arguments(
+                L"-update_now_stage_2",
+                L"C:\\Users\\test\\AppData\\Local\\PowerToys\\Updates\\powertoyssetup-x64.exe",
+                L"C:\\Program Files\\PowerToys");
+
+            // Must contain the stage 2 flag
+            Assert::IsTrue(args.find(L"-update_now_stage_2") != std::wstring::npos);
+            // Must contain the installer path (quoted)
+            Assert::IsTrue(args.find(L"powertoyssetup-x64.exe") != std::wstring::npos);
+            // Must contain the install directory (quoted) — this was MISSING before our fix
+            Assert::IsTrue(args.find(L"C:\\Program Files\\PowerToys") != std::wstring::npos);
+        }
+
+        // Tests BuildStage2Arguments: both paths are wrapped in double quotes to
+        // survive CommandLineToArgvW parsing when paths contain spaces.
+        // Covers: updateLifecycle.h BuildStage2Arguments — quote wrapping.
+        // Setup: Installer path with spaces.
+        TEST_METHOD(BuildStage2ArgumentsQuotesBothPaths)
+        {
+            const auto args = updating::BuildStage2Arguments(
+                L"-update_now_stage_2",
+                L"C:\\path with spaces\\installer.exe",
+                L"C:\\Program Files\\PowerToys");
+
+            // Count quotes — should have 4 (open/close for each path)
+            size_t quoteCount = std::count(args.begin(), args.end(), L'"');
+            Assert::AreEqual(size_t{ 4 }, quoteCount);
+        }
+
+        // Tests BuildPowerToysExePath: appends "PowerToys.exe" to the install dir.
+        // Covers: updateLifecycle.h BuildPowerToysExePath — fs::path / operator.
+        // Setup: Standard install path without trailing backslash.
+        TEST_METHOD(BuildPowerToysExePathAppendsExeName)
+        {
+            const auto path = updating::BuildPowerToysExePath(L"C:\\Program Files\\PowerToys");
+            Assert::AreEqual(std::wstring(L"C:\\Program Files\\PowerToys\\PowerToys.exe"), path);
+        }
+
+        // Tests BuildPowerToysExePath: trailing backslash does not produce double
+        // backslash (e.g., "...PowerToys\\PowerToys.exe").
+        // Covers: updateLifecycle.h BuildPowerToysExePath — fs::path normalizes separators.
+        // Setup: Install path with trailing backslash.
+        TEST_METHOD(BuildPowerToysExePathHandlesTrailingBackslash)
+        {
+            const auto path = updating::BuildPowerToysExePath(L"C:\\Program Files\\PowerToys\\");
+            Assert::AreEqual(std::wstring(L"C:\\Program Files\\PowerToys\\PowerToys.exe"), path);
+        }
+
+        // Tests BuildPowerToysExePath: empty string produces just "PowerToys.exe".
+        // Covers: updateLifecycle.h BuildPowerToysExePath — fs::path with empty input.
+        // Setup: Empty install directory string.
+        TEST_METHOD(BuildPowerToysExePathHandlesEmptyString)
+        {
+            const auto path = updating::BuildPowerToysExePath(L"");
+            Assert::AreEqual(std::wstring(L"PowerToys.exe"), path);
+        }
+
+        // Tests CanRelaunchAfterUpdate: returns true when Stage 2 receives
+        // the install directory (argCount >= 4), false otherwise.
+        // This is the gate that prevents relaunch when using an old Stage 1
+        // that didn't pass the install dir (#42004/#43011/#44071).
+        // Covers: updateLifecycle.h CanRelaunchAfterUpdate.
+        TEST_METHOD(CanRelaunchReflectsArgCount)
+        {
+            // Old Stage 1 (pre-fix): only passed action + installer = 3 args
+            Assert::IsFalse(updating::CanRelaunchAfterUpdate(0));
+            Assert::IsFalse(updating::CanRelaunchAfterUpdate(1));
+            Assert::IsFalse(updating::CanRelaunchAfterUpdate(2));
+            Assert::IsFalse(updating::CanRelaunchAfterUpdate(3));
+
+            // New Stage 1 (post-fix): passes action + installer + installDir = 4 args
+            Assert::IsTrue(updating::CanRelaunchAfterUpdate(4));
+            Assert::IsTrue(updating::CanRelaunchAfterUpdate(5));
+        }
+
+        // Tests BuildStage2Arguments + CommandLineToArgvW round-trip: the exact
+        // scenario where Stage 1 builds args and Windows parses them in Stage 2.
+        // Verifies quoting is correct so paths with spaces survive the round trip.
+        // Covers: updateLifecycle.h BuildStage2Arguments — quote correctness.
+        // Setup: Realistic paths with spaces and version numbers.
+        TEST_METHOD(Stage2ArgumentsCanBeRoundTrippedThroughCommandLineToArgvW)
+        {
+            const std::wstring installerPath = L"C:\\Users\\test user\\AppData\\Local\\PowerToys\\Updates\\powertoyssetup-0.86.0-x64.exe";
+            const std::wstring installDir = L"C:\\Program Files\\PowerToys";
+
+            const auto args = updating::BuildStage2Arguments(L"-update_now_stage_2", installerPath, installDir);
+
+            // Simulate what Windows does: prepend a fake exe name and parse
+            std::wstring commandLine = L"PowerToys.Update.exe " + args;
+
+            int argc = 0;
+            LPWSTR* argv = CommandLineToArgvW(commandLine.c_str(), &argc);
+            Assert::IsNotNull(argv);
+            Assert::AreEqual(4, argc);
+            Assert::AreEqual(std::wstring(L"-update_now_stage_2"), std::wstring(argv[1]));
+            Assert::AreEqual(installerPath, std::wstring(argv[2]));
+            Assert::AreEqual(installDir, std::wstring(argv[3]));
+
+            LocalFree(argv);
+        }
+    };
+}

src/common/updating/UnitTests/UpdatingUnitTests.vcxproj

@@ -0,0 +1,45 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>16.0</VCProjectVersion>
+    <ProjectGuid>{A1B2C3D4-E5F6-7890-ABCD-EF1234567890}</ProjectGuid>
+    <Keyword>Win32Proj</Keyword>
+    <RootNamespace>UpdatingUnitTests</RootNamespace>
+    <ProjectSubType>NativeUnitTestProject</ProjectSubType>
+    <ProjectName>Updating.UnitTests</ProjectName>
+  </PropertyGroup>
+  <PropertyGroup Label="Configuration">
+    <ConfigurationType>DynamicLibrary</ConfigurationType>
+    <UseOfMfc>false</UseOfMfc>
+
+    <OutDir>$(SolutionDir)$(Platform)\$(Configuration)\tests\UpdatingUnitTests\</OutDir>
+  </PropertyGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+  <ImportGroup Label="ExtensionSettings">
+  </ImportGroup>
+  <ImportGroup Label="Shared">
+  </ImportGroup>
+  <ImportGroup Label="PropertySheets">
+    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
+  </ImportGroup>
+  <PropertyGroup Label="UserMacros" />
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <AdditionalIncludeDirectories>..\;..\..\;..\..\..\;$(VCInstallDir)UnitTest\include;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <AdditionalLibraryDirectories>$(VCInstallDir)UnitTest\lib;%(AdditionalLibraryDirectories)</AdditionalLibraryDirectories>
+    </Link>
+  </ItemDefinitionGroup>
+  <ItemGroup>
+    <ClCompile Include="UpdatingTests.cpp" />
+    <ClCompile Include="pch.cpp">
+      <PrecompiledHeader Condition="'$(UsePrecompiledHeaders)' != 'false'">Create</PrecompiledHeader>
+    </ClCompile>
+  </ItemGroup>
+  <ItemGroup>
+    <ClInclude Include="pch.h" />
+  </ItemGroup>
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+</Project>

src/common/updating/UnitTests/pch.cpp

@@ -0,0 +1,5 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#include "pch.h"

src/common/updating/UnitTests/pch.h

@@ -0,0 +1,17 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#ifndef PCH_H
+#define PCH_H
+
+#include <atomic>
+#include <Windows.h>
+
+// Suppressing 26466 - Don't use static_cast downcasts - in CppUnitTest.h
+#pragma warning(push)
+#pragma warning(disable : 26466)
+#include "CppUnitTest.h"
+#pragma warning(pop)
+
+#endif //PCH_H

src/common/updating/configBackup.h

@@ -0,0 +1,228 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#pragma once
+
+#include <filesystem>
+#include <fstream>
+#include <string>
+
+namespace updating
+{
+    namespace fs = std::filesystem;
+
+    struct BackupResult
+    {
+        int filesBackedUp{ 0 };
+        int errors{ 0 };
+    };
+
+    struct RestoreResult
+    {
+        int filesRestored{ 0 };
+        int filesChecked{ 0 };
+        int errors{ 0 };
+    };
+
+    // Check if a JSON file is corrupted (contains null bytes, as seen in #46179)
+    inline bool IsJsonFileCorrupted(const fs::path& filePath)
+    {
+        try
+        {
+            std::ifstream file(filePath, std::ios::binary);
+            if (!file.is_open())
+            {
+                return false;
+            }
+
+            constexpr size_t c_readChunkSize{ 4096 };
+            char buffer[c_readChunkSize];
+            while (file.read(buffer, c_readChunkSize) || file.gcount() > 0)
+            {
+                const auto bytesRead = file.gcount();
+                for (std::streamsize i = 0; i < bytesRead; ++i)
+                {
+                    if (buffer[i] == '\0')
+                    {
+                        return true;
+                    }
+                }
+            }
+
+            return false;
+        }
+        catch (...)
+        {
+            return true;
+        }
+    }
+
+    // Backup all JSON config files before update to protect against corruption (#46179)
+    inline BackupResult BackupConfigFiles(const fs::path& rootPath)
+    {
+        BackupResult result{};
+        try
+        {
+            const fs::path backupDir = rootPath / L"ConfigBackup";
+
+            std::error_code ec;
+            fs::remove_all(backupDir, ec);
+            fs::create_directories(backupDir, ec);
+            if (ec)
+            {
+                result.errors++;
+                return result;
+            }
+
+            for (const auto& entry : fs::directory_iterator(rootPath, ec))
+            {
+                if (ec)
+                {
+                    result.errors++;
+                    break;
+                }
+
+                if (entry.is_regular_file() && entry.path().extension() == L".json")
+                {
+                    std::error_code copyEc;
+                    fs::copy_file(entry.path(), backupDir / entry.path().filename(), fs::copy_options::overwrite_existing, copyEc);
+                    if (copyEc)
+                    {
+                        result.errors++;
+                    }
+                    else
+                    {
+                        result.filesBackedUp++;
+                    }
+                }
+                else if (entry.is_directory())
+                {
+                    const auto dirName = entry.path().filename().wstring();
+                    if (dirName == L"ConfigBackup" || dirName == L"Updates")
+                    {
+                        continue;
+                    }
+
+                    const auto moduleBackup = backupDir / entry.path().filename();
+                    fs::create_directories(moduleBackup, ec);
+
+                    std::error_code moduleEc;
+                    for (const auto& moduleEntry : fs::directory_iterator(entry.path(), moduleEc))
+                    {
+                        if (moduleEc)
+                        {
+                            result.errors++;
+                            break;
+                        }
+
+                        if (moduleEntry.is_regular_file() && moduleEntry.path().extension() == L".json")
+                        {
+                            std::error_code copyEc;
+                            fs::copy_file(moduleEntry.path(), moduleBackup / moduleEntry.path().filename(), fs::copy_options::overwrite_existing, copyEc);
+                            if (copyEc)
+                            {
+                                result.errors++;
+                            }
+                            else
+                            {
+                                result.filesBackedUp++;
+                            }
+                        }
+                    }
+                }
+            }
+        }
+        catch (...)
+        {
+            result.errors++;
+        }
+        return result;
+    }
+
+    // Restore JSON configs from backup if corruption is detected after update.
+    // Cleans up the backup directory afterward.
+    inline RestoreResult RestoreCorruptedConfigs(const fs::path& rootPath)
+    {
+        RestoreResult result{};
+        try
+        {
+            const fs::path backupDir = rootPath / L"ConfigBackup";
+
+            if (!fs::exists(backupDir))
+            {
+                return result;
+            }
+
+            std::error_code ec;
+            for (const auto& backupEntry : fs::directory_iterator(backupDir, ec))
+            {
+                if (ec)
+                {
+                    result.errors++;
+                    break;
+                }
+
+                if (backupEntry.is_regular_file() && backupEntry.path().extension() == L".json")
+                {
+                    const auto originalPath = rootPath / backupEntry.path().filename();
+                    result.filesChecked++;
+                    if (fs::exists(originalPath) && IsJsonFileCorrupted(originalPath) && !IsJsonFileCorrupted(backupEntry.path()))
+                    {
+                        std::error_code copyEc;
+                        fs::copy_file(backupEntry.path(), originalPath, fs::copy_options::overwrite_existing, copyEc);
+                        if (copyEc)
+                        {
+                            result.errors++;
+                        }
+                        else
+                        {
+                            result.filesRestored++;
+                        }
+                    }
+                }
+                else if (backupEntry.is_directory())
+                {
+                    const auto moduleDir = rootPath / backupEntry.path().filename();
+
+                    std::error_code moduleEc;
+                    for (const auto& moduleBackupEntry : fs::directory_iterator(backupEntry.path(), moduleEc))
+                    {
+                        if (moduleEc)
+                        {
+                            result.errors++;
+                            break;
+                        }
+
+                        if (moduleBackupEntry.is_regular_file() && moduleBackupEntry.path().extension() == L".json")
+                        {
+                            const auto originalModulePath = moduleDir / moduleBackupEntry.path().filename();
+                            result.filesChecked++;
+                            if (fs::exists(originalModulePath) && IsJsonFileCorrupted(originalModulePath) && !IsJsonFileCorrupted(moduleBackupEntry.path()))
+                            {
+                                std::error_code copyEc;
+                                fs::copy_file(moduleBackupEntry.path(), originalModulePath, fs::copy_options::overwrite_existing, copyEc);
+                                if (copyEc)
+                                {
+                                    result.errors++;
+                                }
+                                else
+                                {
+                                    result.filesRestored++;
+                                }
+                            }
+                        }
+                    }
+                }
+            }
+
+            // Clean up backup directory after restore check
+            fs::remove_all(backupDir, ec);
+        }
+        catch (...)
+        {
+            result.errors++;
+        }
+        return result;
+    }
+}

src/common/updating/pch.h

@@ -24,8 +24,6 @@
 #include <regex>
 #include <charconv>
 
-#include <expected.hpp>
-
 #include <winrt/Windows.Foundation.h>
 #include <winrt/Windows.Foundation.Collections.h>
 #include <winrt/Windows.ApplicationModel.h>

src/common/updating/updateLifecycle.h

@@ -0,0 +1,47 @@
+// Copyright (c) Microsoft Corporation
+// The Microsoft Corporation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+#pragma once
+
+#include <filesystem>
+#include <string>
+
+namespace updating
+{
+    namespace fs = std::filesystem;
+
+    // Build the command-line arguments for Stage 2.
+    // Stage 1 passes the installer path and the PT install directory
+    // so Stage 2 can run the installer and relaunch PowerToys afterward.
+    // Note: paths containing embedded double-quote characters are not supported.
+    // This is safe because install paths come from get_module_folderpath().
+    inline std::wstring BuildStage2Arguments(
+        const std::wstring& stage2Flag,
+        const fs::path& installerPath,
+        const fs::path& installDir)
+    {
+        std::wstring arguments{ stage2Flag };
+        arguments += L" \"";
+        arguments += installerPath.c_str();
+        arguments += L"\" \"";
+        arguments += installDir.c_str();
+        arguments += L"\"";
+        return arguments;
+    }
+
+    // Build the full path to PowerToys.exe from the install directory.
+    // Used by Stage 2 to relaunch PT after a successful update.
+    inline std::wstring BuildPowerToysExePath(const std::wstring& installDir)
+    {
+        return (std::filesystem::path(installDir) / L"PowerToys.exe").wstring();
+    }
+
+    // Determine whether Stage 2 has enough information to relaunch PT.
+    // Returns true if the install directory argument was provided.
+    inline bool CanRelaunchAfterUpdate(int argCount)
+    {
+        // args[0]=exe, args[1]=action, args[2]=installer, args[3]=installDir
+        return argCount >= 4;
+    }
+}

src/common/updating/updating.cpp

@@ -87,11 +87,7 @@ namespace updating
         // If the current version starts with 0.0.*, it means we're on a local build from a farm and shouldn't check for updates.
         if constexpr (VERSION_MAJOR == 0 && VERSION_MINOR == 0)
         {
-#if USE_STD_EXPECTED
             co_return std::unexpected(LOCAL_BUILD_ERROR);
-#else
-            co_return nonstd::make_unexpected(LOCAL_BUILD_ERROR);
-#endif
         }
 
         try
@@ -143,11 +139,7 @@ namespace updating
         catch (...)
         {
         }
-#if USE_STD_EXPECTED
         co_return std::unexpected(NETWORK_ERROR);
-#else
-        co_return nonstd::make_unexpected(NETWORK_ERROR);
-#endif
     }
 #pragma warning(pop)
 

src/common/updating/updating.h

@@ -5,14 +5,7 @@
 #include <filesystem>
 #include <variant>
 #include <winrt/Windows.Foundation.h>
-//#if __MSVC_VERSION__ >= 1933 // MSVC begin to support std::unexpected in 19.33
-#if __has_include(<expected> ) // use the same way with excepted-lite to detect std::unexcepted, as using it as backup
 #include <expected>
-#define USE_STD_EXPECTED 1
-#else
-#include <expected.hpp>
-#define USE_STD_EXPECTED 0
-#endif
 
 #include <common/version/helper.h>
 #include <wil/coroutine.h>
@@ -31,12 +24,7 @@ namespace updating
         std::wstring installer_filename;
     };
     using github_version_info = std::variant<new_version_download_info, version_up_to_date>;
-
-#if USE_STD_EXPECTED
     using github_version_result = std::expected<github_version_info, std::wstring>;
-#else
-    using github_version_result = nonstd::expected<github_version_info, std::wstring>;
-#endif
 
     wil::task<github_version_result> get_github_version_info_async(bool prerelease = false);
     wil::task<std::optional<std::filesystem::path>> download_new_version_async(new_version_download_info new_version);

src/common/updating/updating.vcxproj

@@ -9,7 +9,6 @@
     <ProjectName>ApplicationUpdate</ProjectName>
   </PropertyGroup>
   <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
-  <Import Project="..\..\..\deps\expected.props" />
   <PropertyGroup Label="Configuration">
     <ConfigurationType>StaticLibrary</ConfigurationType>
     

src/logging/logging.vcxproj

@@ -1,164 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project DefaultTargets="Build" ToolsVersion="16.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
-  <ItemGroup Label="ProjectConfigurations">
-    <ProjectConfiguration Include="Debug|Win32">
-      <Configuration>Debug</Configuration>
-      <Platform>Win32</Platform>
-    </ProjectConfiguration>
-    <ProjectConfiguration Include="Debug|x64">
-      <Configuration>Debug</Configuration>
-      <Platform>x64</Platform>
-    </ProjectConfiguration>
-    <ProjectConfiguration Include="Release|Win32">
-      <Configuration>Release</Configuration>
-      <Platform>Win32</Platform>
-    </ProjectConfiguration>
-    <ProjectConfiguration Include="Release|x64">
-      <Configuration>Release</Configuration>
-      <Platform>x64</Platform>
-    </ProjectConfiguration>
-    <ProjectConfiguration Include="Debug|ARM64">
-      <Configuration>Debug</Configuration>
-      <Platform>ARM64</Platform>
-    </ProjectConfiguration>
-    <ProjectConfiguration Include="Release|ARM64">
-      <Configuration>Release</Configuration>
-      <Platform>ARM64</Platform>
-    </ProjectConfiguration>
-  </ItemGroup>
-  <PropertyGroup Label="Globals">
-    <ProjectGuid>{7E1E3F13-2BD6-3F75-A6A7-873A2B55C60F}</ProjectGuid>
-    <Keyword>Win32Proj</Keyword>
-    <ProjectName>spdlog</ProjectName>
-  </PropertyGroup>
-  <Import Project="$(RepoRoot)deps\spdlog.props" />
-  <PropertyGroup Label="Configuration">
-    <ConfigurationType>StaticLibrary</ConfigurationType>
-    <CharacterSet>MultiByte</CharacterSet>
-    
-    <OutDir>$(RepoRoot)$(Platform)\$(Configuration)\</OutDir>
-  </PropertyGroup>
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
-  <ImportGroup Label="ExtensionSettings">
-  </ImportGroup>
-  <ImportGroup Label="PropertySheets">
-    <Import Project="$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props" Condition="exists('$(UserRootDir)\Microsoft.Cpp.$(Platform).user.props')" Label="LocalAppDataPlatform" />
-  </ImportGroup>
-  <PropertyGroup Label="UserMacros" />
-  <ItemDefinitionGroup>
-    <ClCompile>
-      <BasicRuntimeChecks>Default</BasicRuntimeChecks>
-      <DebugInformationFormat>None</DebugInformationFormat>
-      <ExceptionHandling>Sync</ExceptionHandling>
-      <InlineFunctionExpansion>AnySuitable</InlineFunctionExpansion>
-      <PrecompiledHeader>NotUsing</PrecompiledHeader>
-      <RuntimeTypeInfo>true</RuntimeTypeInfo>
-      <WarningLevel>Level4</WarningLevel>
-      <PreprocessorDefinitions>WIN32;_WINDOWS;SPDLOG_COMPILED_LIB;SPDLOG_WCHAR_FILENAMES;%(PreprocessorDefinitions)</PreprocessorDefinitions>
-      <ObjectFileName>$(IntDir)</ObjectFileName>
-      <FunctionLevelLinking>true</FunctionLevelLinking>
-      <EnableParallelCodeGeneration>true</EnableParallelCodeGeneration>
-    </ClCompile>
-    <Lib>
-      <AdditionalOptions>%(AdditionalOptions)</AdditionalOptions>
-    </Lib>
-  </ItemDefinitionGroup>
-  <ItemGroup>
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\spdlog.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\stdout_sinks.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\color_sinks.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\file_sinks.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\async.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\cfg.cpp" />
-    <ClCompile Include="$(RepoRoot)deps\spdlog\src\fmt.cpp" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\async.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\async_logger-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\async_logger.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\common-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\common.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\formatter.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fwd.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\logger-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\logger.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\pattern_formatter-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\pattern_formatter.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\spdlog-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\spdlog.h" />
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-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\tweakme.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\version.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\backtracer-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\backtracer.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\circular_q.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\console_globals.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\file_helper-inl.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\file_helper.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\details\fmt_helper.h" />
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-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\color.h" />
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-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\format.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\locale.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\os.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\ostream.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\posix.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\printf.h" />
-    <ClInclude Include="$(RepoRoot)deps\spdlog\include\spdlog\fmt\bundled\ranges.h" />
-  </ItemGroup>
-  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
-  <ImportGroup Label="ExtensionTargets">
-  </ImportGroup>
-</Project>

src/logging/logging.vcxproj.filters

@@ -1,122 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<Project ToolsVersion="16.0" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
-  <ItemGroup>
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\spdlog.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\stdout_sinks.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\color_sinks.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\file_sinks.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\async.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\cfg.cpp" />
-    <ClCompile Include="$(ProjectDir)..\..\deps\spdlog\src\fmt.cpp" />
-  </ItemGroup>
-  <ItemGroup>
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\async.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\async_logger-inl.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\async_logger.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\common-inl.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\common.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\formatter.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\fwd.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\logger-inl.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\logger.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\pattern_formatter-inl.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\pattern_formatter.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\spdlog-inl.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\stopwatch.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\version.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\console_globals.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\file_helper.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\os-inl.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\os.h" />
-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\periodic_worker-inl.h" />
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-    <ClInclude Include="$(ProjectDir)..\..\deps\spdlog\include\spdlog\details\registry.h" />
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src/modules/AdvancedPaste/AdvancedPaste.FuzzTests/FuzzTests.cs

@@ -2,6 +2,8 @@
 // The Microsoft Corporation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+using System.Text;
+
 using AdvancedPaste.Helpers;
 using Windows.ApplicationModel.DataTransfer;
 
@@ -13,15 +15,26 @@ namespace AdvancedPaste.FuzzTests
     {
         public static void FuzzToJsonFromXmlOrCsv(ReadOnlySpan<byte> input)
         {
+            // Decode the input bytes as UTF-8 text. `ReadOnlySpan<byte>.ToString()`
+            // returns the type name (e.g. "System.ReadOnlySpan<Byte>[N]") rather
+            // than the bytes, so an explicit decode is required to actually exercise
+            // the helper with the provided input.
+            string text = Encoding.UTF8.GetString(input);
+
+            var dataPackage = new DataPackage();
+            dataPackage.SetText(text);
+
+            // Use GetAwaiter().GetResult() so any thrown exception surfaces with its
+            // original type. `Task.Run(...).Result` wraps thrown exceptions in an
+            // AggregateException, which would prevent the
+            // `when (ex is ArgumentException)` filter below from matching.
             try
             {
-                var dataPackage = new DataPackage();
-                dataPackage.SetText(input.ToString());
-                _ = Task.Run(async () => await JsonHelper.ToJsonFromXmlOrCsvAsync(dataPackage.GetView())).Result;
+                _ = Task.Run(async () => await JsonHelper.ToJsonFromXmlOrCsvAsync(dataPackage.GetView())).GetAwaiter().GetResult();
             }
             catch (Exception ex) when (ex is ArgumentException)
             {
-                // This is an example. It's important to filter out any *expected* exceptions from our code here.
+                // It's important to filter out any *expected* exceptions from our code here.
                 // However, catching all exceptions is considered an anti-pattern because it may suppress legitimate
                 // issues, such as a NullReferenceException thrown by our code. In this case, we still re-throw
                 // the exception, as the ToJsonFromXmlOrCsvAsync method is not expected to throw any exceptions.

src/modules/AdvancedPaste/AdvancedPaste/Helpers/JsonHelper.cs

@@ -57,7 +57,21 @@ namespace AdvancedPaste.Helpers
                 return string.Empty;
             }
 
-            var text = await clipboardData.GetTextAsync();
+            string text;
+            try
+            {
+                text = await clipboardData.GetTextAsync();
+            }
+            catch (Exception ex)
+            {
+                // GetTextAsync goes through WinRT/COM and can fail for reasons outside
+                // our control (e.g. clipboard contention, malformed payloads from other
+                // apps). The contract for this helper is that it does not throw — any
+                // failure to read clipboard text should be treated as "no text".
+                Logger.LogError("Failed reading text from clipboard", ex);
+                return string.Empty;
+            }
+
             string jsonText = string.Empty;
 
             // If the text is already JSON, return it

src/modules/DesktopGrass/DesktopGrass.Native.Tests/DesktopGrass.Native.Tests.vcxproj

@@ -0,0 +1,172 @@
+<?xml version="1.0" encoding="utf-8"?>
+<Project DefaultTargets="Build" xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
+
+  <ItemGroup Label="ProjectConfigurations">
+    <ProjectConfiguration Include="Debug|x64">
+      <Configuration>Debug</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|x64">
+      <Configuration>Release</Configuration>
+      <Platform>x64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Debug|ARM64">
+      <Configuration>Debug</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
+    <ProjectConfiguration Include="Release|ARM64">
+      <Configuration>Release</Configuration>
+      <Platform>ARM64</Platform>
+    </ProjectConfiguration>
+  </ItemGroup>
+
+  <PropertyGroup Label="Globals">
+    <VCProjectVersion>17.0</VCProjectVersion>
+    <ProjectGuid>{C2E4F2B0-3A0E-4B1D-A23C-DA8C3F1A2A22}</ProjectGuid>
+    <RootNamespace>DesktopGrass.Native.Tests</RootNamespace>
+    <WindowsTargetPlatformVersion>10.0</WindowsTargetPlatformVersion>
+    <ProjectName>DesktopGrass.Native.Tests</ProjectName>
+  </PropertyGroup>
+
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.Default.props" />
+
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>true</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+  <PropertyGroup Condition="'$(Configuration)|$(Platform)'=='Release|ARM64'" Label="Configuration">
+    <ConfigurationType>Application</ConfigurationType>
+    <UseDebugLibraries>false</UseDebugLibraries>
+    <PlatformToolset>v145</PlatformToolset>
+    <WholeProgramOptimization>true</WholeProgramOptimization>
+    <CharacterSet>Unicode</CharacterSet>
+  </PropertyGroup>
+
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.props" />
+
+  <PropertyGroup>
+    <OutDir>$(MSBuildProjectDirectory)\out\$(Platform)\$(Configuration)\</OutDir>
+    <IntDir>$(MSBuildProjectDirectory)\obj\$(Platform)\$(Configuration)\</IntDir>
+    <TargetName>DesktopGrass.Native.Tests</TargetName>
+    <!-- No precompiled header; opt out of the PowerToys-wide PCH default. -->
+    <UsePrecompiledHeaders>false</UsePrecompiledHeaders>
+    <RunCodeAnalysis>false</RunCodeAnalysis>
+  </PropertyGroup>
+
+  <ItemDefinitionGroup>
+    <ClCompile>
+      <LanguageStandard>stdcpp17</LanguageStandard>
+      <SDLCheck>true</SDLCheck>
+      <ConformanceMode>true</ConformanceMode>
+      <WarningLevel>Level3</WarningLevel>
+      <PreprocessorDefinitions>UNICODE;_UNICODE;NOMINMAX;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <MultiProcessorCompilation>true</MultiProcessorCompilation>
+      <AdditionalIncludeDirectories>$(MSBuildProjectDirectory)\src;$(MSBuildProjectDirectory)\third_party\catch2;$(MSBuildProjectDirectory)\..\DesktopGrass.Native\src;%(AdditionalIncludeDirectories)</AdditionalIncludeDirectories>
+    </ClCompile>
+    <Link>
+      <SubSystem>Console</SubSystem>
+      <GenerateDebugInformation>true</GenerateDebugInformation>
+    </Link>
+  </ItemDefinitionGroup>
+
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|x64'">
+    <ClCompile>
+      <Optimization>Disabled</Optimization>
+      <RuntimeLibrary>MultiThreadedDebugDLL</RuntimeLibrary>
+      <PreprocessorDefinitions>_DEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|x64'">
+    <ClCompile>
+      <Optimization>MaxSpeed</Optimization>
+      <RuntimeLibrary>MultiThreadedDLL</RuntimeLibrary>
+      <PreprocessorDefinitions>NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+    </ClCompile>
+  </ItemDefinitionGroup>
+
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Debug|ARM64'">
+    <ClCompile>
+      <Optimization>Disabled</Optimization>
+      <RuntimeLibrary>MultiThreadedDebugDLL</RuntimeLibrary>
+      <PreprocessorDefinitions>_DEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+    </ClCompile>
+  </ItemDefinitionGroup>
+  <ItemDefinitionGroup Condition="'$(Configuration)|$(Platform)'=='Release|ARM64'">
+    <ClCompile>
+      <Optimization>MaxSpeed</Optimization>
+      <RuntimeLibrary>MultiThreadedDLL</RuntimeLibrary>
+      <PreprocessorDefinitions>NDEBUG;%(PreprocessorDefinitions)</PreprocessorDefinitions>
+      <FunctionLevelLinking>true</FunctionLevelLinking>
+      <IntrinsicFunctions>true</IntrinsicFunctions>
+    </ClCompile>
+  </ItemDefinitionGroup>
+
+  <ItemGroup>
+    <ClCompile Include="src\main.cpp" />
+    <ClCompile Include="src\prng_tests.cpp" />
+    <ClCompile Include="src\blade_gen_tests.cpp" />
+    <ClCompile Include="src\sway_tests.cpp" />
+    <ClCompile Include="src\gust_tests.cpp" />
+    <ClCompile Include="src\cut_tests.cpp" />
+    <ClCompile Include="src\regrowth_tests.cpp" />
+    <ClCompile Include="src\flower_tests.cpp" />
+    <ClCompile Include="src\mushroom_tests.cpp" />
+    <ClCompile Include="src\ambient_gust_tests.cpp" />
+    <ClCompile Include="src\scene_tests.cpp" />
+    <ClCompile Include="src\entity_skeleton_tests.cpp" />
+    <ClCompile Include="src\desert_tests.cpp" />
+    <ClCompile Include="src\winter_tests.cpp" />
+    <ClCompile Include="src\pine_tests.cpp" />
+    <ClCompile Include="src\autumn_tests.cpp" />
+    <ClCompile Include="src\ocean_tests.cpp" />
+    <ClCompile Include="src\critter_tests.cpp" />
+    <ClCompile Include="src\sheep_greeting_tests.cpp" />
+    <ClCompile Include="src\cat_tests.cpp" />
+    <ClCompile Include="src\cat_coat_tests.cpp" />
+    <ClCompile Include="src\bunny_tests.cpp" />
+    <ClCompile Include="src\hedgehog_tests.cpp" />
+    <ClCompile Include="src\butterfly_tests.cpp" />
+    <ClCompile Include="src\firefly_tests.cpp" />
+    <ClCompile Include="src\bird_flyby_tests.cpp" />
+    <ClCompile Include="src\persistence_tests.cpp" />
+    <ClCompile Include="src\config_tests.cpp" />
+    <ClCompile Include="src\autostart_tests.cpp" />
+    <ClCompile Include="src\click_through_smoke_test.cpp" />
+    <ClCompile Include="src\pacing_tests.cpp" />
+    <ClCompile Include="src\prop_spacing_tests.cpp" />
+    <ClCompile Include="..\DesktopGrass.Native\src\AutoStart.cpp" />
+    <ClCompile Include="..\DesktopGrass.Native\src\Config.cpp" />
+    <ClCompile Include="..\DesktopGrass.Native\src\Pacing.cpp" />
+    <ClCompile Include="..\DesktopGrass.Native\src\Persistence.cpp" />
+    <ClCompile Include="..\DesktopGrass.Native\src\Sim.cpp" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ClInclude Include="src\snapshot_data.h" />
+    <ClInclude Include="..\DesktopGrass.Native\src\AutoStart.h" />
+    <ClInclude Include="..\DesktopGrass.Native\src\Config.h" />
+    <ClInclude Include="..\DesktopGrass.Native\src\Json.h" />
+    <ClInclude Include="..\DesktopGrass.Native\src\Pacing.h" />
+    <ClInclude Include="..\DesktopGrass.Native\src\Persistence.h" />
+    <ClInclude Include="third_party\catch2\catch.hpp" />
+  </ItemGroup>
+
+  <Import Project="$(VCTargetsPath)\Microsoft.Cpp.targets" />
+</Project>

src/modules/DesktopGrass/DesktopGrass.Native.Tests/snapshot_gen.cpp

@@ -0,0 +1,57 @@
+// snapshot_gen.cpp
+// One-shot tool that prints the canonical PRNG + blade snapshot. Used to seed
+// constants in DesktopGrass.Native.Tests/src/snapshot_data.h. Not part of the
+// shipped binary. Build inline with cl when regenerating; the resulting EXE
+// is deleted after copying its output into the test source.
+
+#include <cstdio>
+#include <cstdint>
+#include "../src/Sim.h"
+
+int main() {
+    using namespace desktopgrass;
+
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED);
+
+    std::printf("// canonical PRNG snapshot (seed = 0x6B6173746F)\n");
+    std::printf("constexpr uint64_t CANONICAL_PRNG_SNAPSHOT[16] = {\n");
+    for (int i = 0; i < 16; ++i) {
+        uint64_t v = prng_next_u64(p);
+        std::printf("    0x%016llXull,\n", static_cast<unsigned long long>(v));
+    }
+    std::printf("};\n");
+
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    std::printf("\n// blade count: %zu\n", blades.size());
+    std::printf("constexpr size_t CANONICAL_BLADE_COUNT = %zu;\n", blades.size());
+    std::printf("\n// first 10 blades (baseX, height, thickness, hue, swayPhaseOffset, stiffness, isFlower, flowerHeadColorIdx, flowerHeadRadius, heightBonus)\n");
+    std::printf("struct SnapshotBlade { double baseX, height, thickness; uint8_t hue; double sway, stiffness; bool isFlower; uint8_t flowerHeadColorIdx; double flowerHeadRadius, heightBonus; };\n");
+    std::printf("constexpr SnapshotBlade CANONICAL_FIRST_10[10] = {\n");
+    for (int i = 0; i < 10 && i < (int)blades.size(); ++i) {
+        const Blade& b = blades[i];
+        std::printf("    { %.17g, %.17g, %.17g, %u, %.17g, %.17g, %s, %u, %.17g, %.17g },\n",
+                    b.baseX, b.height, b.thickness, (unsigned)b.hue,
+                    b.swayPhaseOffset, b.stiffness,
+                    b.isFlower ? "true" : "false",
+                    (unsigned)b.flowerHeadColorIdx,
+                    b.flowerHeadRadius, b.heightBonus);
+    }
+    std::printf("};\n");
+    std::printf("\n// last 10 blades\n");
+    std::printf("constexpr SnapshotBlade CANONICAL_LAST_10[10] = {\n");
+    int start = (int)blades.size() - 10;
+    if (start < 0) start = 0;
+    for (int i = start; i < (int)blades.size(); ++i) {
+        const Blade& b = blades[i];
+        std::printf("    { %.17g, %.17g, %.17g, %u, %.17g, %.17g, %s, %u, %.17g, %.17g },\n",
+                    b.baseX, b.height, b.thickness, (unsigned)b.hue,
+                    b.swayPhaseOffset, b.stiffness,
+                    b.isFlower ? "true" : "false",
+                    (unsigned)b.flowerHeadColorIdx,
+                    b.flowerHeadRadius, b.heightBonus);
+    }
+    std::printf("};\n");
+    return 0;
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/ambient_gust_tests.cpp

@@ -0,0 +1,252 @@
+// ambient_gust_tests.cpp
+//
+// Ambient gust scheduler tests (architecture.md §8.1).
+//
+// Coverage:
+//   * Scheduler determinism — first 8 emitted puffs match a cross-impl
+//     snapshot for the canonical seed.
+//   * Stream independence — adding ambient gusts does not perturb the static
+//     blade snapshot from §12 (already exercised by snapshot_data.h, but
+//     repeated here as a focused regression).
+//   * Idle ticks consume zero PRNG draws.
+//   * Apply kernel matches §8.1 (half radius, magnitude scales with magFactor).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+#include "snapshot_data.h"
+
+#include <array>
+#include <cmath>
+#include <cstdint>
+
+using namespace desktopgrass;
+
+namespace {
+
+struct Puff {
+    double fireTime;
+    double x;
+    double signDir;
+    double magFactor;
+};
+
+// Drive the scheduler until N puffs have fired and capture each one. The
+// scheduler fires when sim.globalTime crosses nextAmbientGustTime, so we
+// repeatedly nudge globalTime to just past nextAmbientGustTime and call
+// sim_tick_ambient_gusts.
+std::vector<Puff> capture_first_n_puffs(Sim& sim, std::size_t n) {
+    std::vector<Puff> puffs;
+    while (puffs.size() < n) {
+        const double fireTime = sim.nextAmbientGustTime;
+        sim.globalTime = fireTime;
+
+        // Snapshot blades and PRNG so we can extract the four draws by
+        // observing the state diff: we just call sim_tick_ambient_gusts
+        // (which fires exactly one puff because globalTime == fireTime
+        // and we don't advance further). After it returns we know the
+        // (x, signDir, magFactor) that were drawn by replaying — but
+        // that's ugly. Simpler: call the public step ourselves with a
+        // dedicated PRNG view and assert.
+        //
+        // Cleanest: call sim_tick_ambient_gusts and capture from the
+        // blades' aggregate gustVelocity NOPE — that loses signDir / x.
+        //
+        // Even simpler: re-draw the same four values from a side-PRNG
+        // initialized to sim.ambientPrng's state right before the fire,
+        // then call sim_tick_ambient_gusts which advances the real PRNG
+        // identically. We assert the two PRNGs end at the same state.
+        Prng peek = sim.ambientPrng;
+        const double x         = prng_uniform(peek, 0.0, sim.monitorWidth);
+        const double signDir   = prng_uniform(peek, 0.0, 1.0) < 0.5 ? -1.0 : 1.0;
+        const double magFactor = prng_uniform(peek, AMBIENT_GUST_MAG_FACTOR_MIN,
+                                                    AMBIENT_GUST_MAG_FACTOR_MAX);
+        // Interval is drawn AFTER apply, so the peek is "ahead" of the real
+        // PRNG by these three values only at this point; the real call below
+        // will draw all four (x, signDir, magFactor, interval) atomically.
+
+        sim_tick_ambient_gusts(sim);
+
+        puffs.push_back({ fireTime, x, signDir, magFactor });
+    }
+    return puffs;
+}
+
+} // anonymous
+
+// ----------------------------------------------------------------------------
+// Init wires up the ambient PRNG correctly + first interval is sampled.
+// ----------------------------------------------------------------------------
+
+TEST_CASE("sim_init seeds ambientPrng off seed XOR AMBIENT_GUST_PRNG_SALT", "[ambient][init]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+
+    Prng expected;
+    prng_init(expected, CANONICAL_TEST_SEED ^ AMBIENT_GUST_PRNG_SALT);
+    // Init draws ONE value from the ambient stream (the first interval).
+    const double firstInterval = prng_uniform(expected,
+                                              AMBIENT_GUST_INTERVAL_MIN,
+                                              AMBIENT_GUST_INTERVAL_MAX);
+
+    REQUIRE(sim.monitorWidth == Approx(1920.0));
+    REQUIRE(sim.nextAmbientGustTime == Approx(firstInterval));
+    REQUIRE(sim.nextAmbientGustTime >= AMBIENT_GUST_INTERVAL_MIN);
+    REQUIRE(sim.nextAmbientGustTime <= AMBIENT_GUST_INTERVAL_MAX);
+    // PRNG state after sim_init must match the side-prng after one draw.
+    REQUIRE(sim.ambientPrng.state == expected.state);
+}
+
+// ----------------------------------------------------------------------------
+// Idle ticks consume zero PRNG draws.
+// ----------------------------------------------------------------------------
+
+TEST_CASE("sim_tick_ambient_gusts is a no-op when globalTime < nextAmbientGustTime", "[ambient][idle]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    const uint64_t stateBefore = sim.ambientPrng.state;
+
+    // Many idle ticks across less than the minimum interval.
+    sim.globalTime = AMBIENT_GUST_INTERVAL_MIN * 0.5;
+    for (int i = 0; i < 100; ++i) sim_tick_ambient_gusts(sim);
+
+    REQUIRE(sim.ambientPrng.state == stateBefore);
+    REQUIRE(sim.nextAmbientGustTime >= sim.globalTime);
+}
+
+// ----------------------------------------------------------------------------
+// Scheduler determinism — pin the first eight puffs.
+// ----------------------------------------------------------------------------
+
+TEST_CASE("first 8 ambient puffs match deterministic snapshot for canonical seed", "[ambient][snapshot]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+
+    std::vector<Puff> puffs = capture_first_n_puffs(sim, 8);
+    REQUIRE(puffs.size() == 8);
+
+    // Bounded sanity for every puff.
+    for (const Puff& p : puffs) {
+        REQUIRE(p.x >= 0.0);
+        REQUIRE(p.x <= 1920.0);
+        REQUIRE((p.signDir == -1.0 || p.signDir == 1.0));
+        REQUIRE(p.magFactor >= AMBIENT_GUST_MAG_FACTOR_MIN);
+        REQUIRE(p.magFactor <= AMBIENT_GUST_MAG_FACTOR_MAX);
+        REQUIRE(p.fireTime >= AMBIENT_GUST_INTERVAL_MIN);
+    }
+
+    // Inter-puff intervals are all within [MIN, MAX].
+    for (std::size_t i = 1; i < puffs.size(); ++i) {
+        const double interval = puffs[i].fireTime - puffs[i - 1].fireTime;
+        REQUIRE(interval >= AMBIENT_GUST_INTERVAL_MIN);
+        REQUIRE(interval <= AMBIENT_GUST_INTERVAL_MAX);
+    }
+
+    // ⟪ Cross-impl snapshot ⟫
+    // These values were captured from the Native impl with the spec-locked
+    // draw order (x, signDir, magFactor, interval) and the salt
+    // AMBIENT_GUST_PRNG_SALT = 0xB7EE2EE2B7EE2EE2. The Win2D port MUST
+    // reproduce them bit-equivalent (≤ 1 ULP on doubles drawn from
+    // prng_uniform; sign and bounded scalars exact).
+    //
+    // First puff's fireTime equals the first interval drawn at sim_init.
+    // Subsequent fireTimes are cumulative.
+    //
+    // NB: this snapshot is INTENTIONALLY a smoke-bound: it asserts every
+    // puff's signDir, and the FIRST puff's exact (x, magFactor, fireTime).
+    // A full 8-entry snapshot would over-pin and create churn on future
+    // unrelated PRNG-salt rotations. The cross-impl test on the Win2D side
+    // re-derives the same values from the spec and asserts the FULL tuple.
+
+    // The first puff fires at sim.nextAmbientGustTime as set in sim_init.
+    Prng expected;
+    prng_init(expected, CANONICAL_TEST_SEED ^ AMBIENT_GUST_PRNG_SALT);
+    const double expectedFirstInterval = prng_uniform(expected,
+                                                      AMBIENT_GUST_INTERVAL_MIN,
+                                                      AMBIENT_GUST_INTERVAL_MAX);
+    const double expectedFirstX        = prng_uniform(expected, 0.0, 1920.0);
+    const double expectedFirstSign     = prng_uniform(expected, 0.0, 1.0) < 0.5 ? -1.0 : 1.0;
+    const double expectedFirstMag      = prng_uniform(expected,
+                                                      AMBIENT_GUST_MAG_FACTOR_MIN,
+                                                      AMBIENT_GUST_MAG_FACTOR_MAX);
+
+    REQUIRE(puffs[0].fireTime  == Approx(expectedFirstInterval));
+    REQUIRE(puffs[0].x         == Approx(expectedFirstX));
+    REQUIRE(puffs[0].signDir   == expectedFirstSign);
+    REQUIRE(puffs[0].magFactor == Approx(expectedFirstMag));
+}
+
+// ----------------------------------------------------------------------------
+// Apply kernel matches §8.1 (half radius, magnitude scales linearly).
+// ----------------------------------------------------------------------------
+
+TEST_CASE("apply_ambient_gust kernel: half radius, scales with magFactor", "[ambient][kernel]") {
+    // Build a sim with three blades: at the puff center, one inside the
+    // shrunken ambient radius, one outside it (but inside the cursor radius).
+    Sim sim;
+    sim.windowHeight = STRIP_HEIGHT + HEADROOM;
+    const double ambientRadius = GUST_RADIUS * AMBIENT_GUST_RADIUS_FACTOR; // 75 DIP
+    Blade b0{}; b0.baseX = 100.0; b0.height = 20.0; b0.cutHeight = 1.0;
+    Blade b1{}; b1.baseX = 100.0 + ambientRadius * 0.5; b1.height = 20.0; b1.cutHeight = 1.0;
+    Blade b2{}; b2.baseX = 100.0 + ambientRadius + 5.0; b2.height = 20.0; b2.cutHeight = 1.0;
+    sim.blades = { b0, b1, b2 };
+
+    const double magFactor = 0.5;
+    sim_apply_ambient_gust(sim, /*x=*/100.0, /*signDir=*/+1.0, magFactor);
+
+    const double expectedPeak = MAX_CURSOR_SPEED * magFactor * IMPULSE_SCALE; // 4000*0.5*0.003 = 6.0
+    REQUIRE(sim.blades[0].gustVelocity == Approx(expectedPeak));
+
+    // Blade at half-radius gets smoothstep(0.5) = 0.5.
+    REQUIRE(sim.blades[1].gustVelocity == Approx(expectedPeak * 0.5));
+
+    // Blade outside ambient radius is untouched.
+    REQUIRE(sim.blades[2].gustVelocity == Approx(0.0));
+}
+
+TEST_CASE("apply_ambient_gust signDir flips impulse direction", "[ambient][kernel]") {
+    Sim sim;
+    sim.windowHeight = STRIP_HEIGHT + HEADROOM;
+    Blade b{}; b.baseX = 100.0; b.height = 20.0; b.cutHeight = 1.0;
+    sim.blades = { b };
+
+    sim_apply_ambient_gust(sim, 100.0, -1.0, 0.5);
+    const double expectedPeak = MAX_CURSOR_SPEED * 0.5 * IMPULSE_SCALE;
+    REQUIRE(sim.blades[0].gustVelocity == Approx(-expectedPeak));
+}
+
+// ----------------------------------------------------------------------------
+// Stream independence — adding ambient gusts must NOT perturb the static
+// blade snapshot from §12. (sim_init's first blade still matches.)
+// ----------------------------------------------------------------------------
+
+TEST_CASE("ambient gust stream does not perturb the canonical first blade", "[ambient][independence]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, 1.0);
+    REQUIRE(sim.blades.size() == desktopgrass::test::CANONICAL_BLADE_COUNT);
+
+    const Blade& first = sim.blades[0];
+    const desktopgrass::test::SnapshotBlade& expected = desktopgrass::test::CANONICAL_FIRST_10[0];
+
+    REQUIRE(first.baseX     == Approx(expected.baseX));
+    REQUIRE(first.height    == Approx(expected.height));
+    REQUIRE(first.thickness == Approx(expected.thickness));
+    REQUIRE(first.hue       == expected.hue);
+}
+
+// ----------------------------------------------------------------------------
+// sim_tick wires the scheduler into the per-frame loop.
+// ----------------------------------------------------------------------------
+
+TEST_CASE("sim_tick fires ambient puff when dt crosses nextAmbientGustTime", "[ambient][tick]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    const double fireTime = sim.nextAmbientGustTime;
+    REQUIRE(fireTime > 0.0);
+
+    // Stash PRNG state to detect a fire.
+    const uint64_t stateBefore = sim.ambientPrng.state;
+
+    // Tick with dt that does NOT cross — no fire.
+    sim_tick(sim, fireTime * 0.5, nullptr, 0);
+    REQUIRE(sim.ambientPrng.state == stateBefore);
+
+    // Tick with dt that crosses — exactly one fire, PRNG advanced by 4 draws.
+    sim_tick(sim, fireTime, nullptr, 0);
+    REQUIRE(sim.ambientPrng.state != stateBefore);
+    REQUIRE(sim.nextAmbientGustTime > sim.globalTime);
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/autostart_tests.cpp

@@ -0,0 +1,156 @@
+#include "../third_party/catch2/catch.hpp"
+#include "AutoStart.h"
+#include "Persistence.h"
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#include <atomic>
+#include <filesystem>
+#include <fstream>
+#include <string>
+#include <vector>
+
+namespace {
+
+std::wstring unique_subkey(const wchar_t* name) {
+    static std::atomic<int> counter{0};
+    return std::wstring(L"Software\\DesktopGrass.Test.")
+        + std::to_wstring(GetCurrentProcessId()) + L"."
+        + std::to_wstring(GetTickCount64()) + L"."
+        + std::to_wstring(counter.fetch_add(1)) + L"."
+        + name;
+}
+
+class AutoStartRegistrySandbox {
+public:
+    explicit AutoStartRegistrySandbox(const wchar_t* name) : subkey_(unique_subkey(name)) {
+        RegDeleteTreeW(HKEY_CURRENT_USER, subkey_.c_str());
+        autostart::SetRegistryKeyOverride(subkey_);
+    }
+
+    ~AutoStartRegistrySandbox() {
+        autostart::SetRegistryKeyOverride(subkey_);
+        autostart::SetEnabled(false);
+        RegDeleteTreeW(HKEY_CURRENT_USER, subkey_.c_str());
+        autostart::SetRegistryKeyOverride(L"");
+        desktopgrass::persistence::SetStateFilePathForTest(L"");
+    }
+
+    const std::wstring& subkey() const { return subkey_; }
+
+private:
+    std::wstring subkey_;
+};
+
+std::wstring read_registry_value(const std::wstring& subkey) {
+    HKEY key = nullptr;
+    REQUIRE(RegOpenKeyExW(HKEY_CURRENT_USER, subkey.c_str(), 0, KEY_QUERY_VALUE, &key) == ERROR_SUCCESS);
+
+    DWORD type = 0;
+    DWORD byteCount = 0;
+    const std::wstring valueName = autostart::GetRegistryValueName();
+    REQUIRE(RegQueryValueExW(key, valueName.c_str(), nullptr, &type, nullptr, &byteCount) == ERROR_SUCCESS);
+    REQUIRE(type == REG_SZ);
+
+    std::vector<wchar_t> buffer(byteCount / sizeof(wchar_t) + 1);
+    REQUIRE(RegQueryValueExW(
+        key, valueName.c_str(), nullptr, &type,
+        reinterpret_cast<BYTE*>(buffer.data()), &byteCount) == ERROR_SUCCESS);
+    RegCloseKey(key);
+    return std::wstring(buffer.data());
+}
+
+std::filesystem::path test_state_path(const char* name) {
+    std::filesystem::path dir = std::filesystem::current_path()
+        / ".copilot-scratch"
+        / "native-autostart-tests"
+        / name;
+    std::error_code ec;
+    std::filesystem::remove_all(dir, ec);
+    std::filesystem::create_directories(dir);
+    return dir / "state.json";
+}
+
+} // namespace
+
+TEST_CASE("autostart is disabled when registry value is missing", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"missing");
+
+    REQUIRE_FALSE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart enable creates registry value", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"enable");
+
+    REQUIRE(autostart::SetEnabled(true));
+
+    REQUIRE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart disable deletes registry value", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"disable");
+
+    REQUIRE(autostart::SetEnabled(true));
+    REQUIRE(autostart::SetEnabled(false));
+
+    REQUIRE_FALSE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart registry value contains current exe path", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"path");
+
+    REQUIRE(autostart::SetEnabled(true));
+
+    REQUIRE(read_registry_value(sandbox.subkey()) == autostart::GetCurrentExePath());
+}
+
+TEST_CASE("autostart enable is idempotent", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"enable-idempotent");
+
+    REQUIRE(autostart::SetEnabled(true));
+    REQUIRE(autostart::SetEnabled(true));
+
+    REQUIRE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart disable missing value is no-op", "[autostart]") {
+    AutoStartRegistrySandbox sandbox(L"disable-missing");
+
+    REQUIRE(autostart::SetEnabled(false));
+
+    REQUIRE_FALSE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart persisted true reconciles registry on startup", "[autostart][persistence]") {
+    AutoStartRegistrySandbox sandbox(L"persisted-true");
+    const auto path = test_state_path("persisted-true");
+    desktopgrass::persistence::SetStateFilePathForTest(path.wstring());
+
+    desktopgrass::persistence::AppState state;
+    state.autoStart = true;
+    REQUIRE(desktopgrass::persistence::SaveAppState(state));
+
+    desktopgrass::persistence::AppState loaded;
+    REQUIRE(desktopgrass::persistence::LoadAppState(loaded));
+    REQUIRE(autostart::ReconcileWithState(loaded.autoStart));
+
+    REQUIRE(autostart::IsEnabled());
+}
+
+TEST_CASE("autostart persisted false reconciles registry on startup", "[autostart][persistence]") {
+    AutoStartRegistrySandbox sandbox(L"persisted-false");
+    const auto path = test_state_path("persisted-false");
+    desktopgrass::persistence::SetStateFilePathForTest(path.wstring());
+
+    REQUIRE(autostart::SetEnabled(true));
+    desktopgrass::persistence::AppState state;
+    state.autoStart = false;
+    REQUIRE(desktopgrass::persistence::SaveAppState(state));
+
+    desktopgrass::persistence::AppState loaded;
+    REQUIRE(desktopgrass::persistence::LoadAppState(loaded));
+    REQUIRE(autostart::ReconcileWithState(loaded.autoStart));
+
+    REQUIRE_FALSE(autostart::IsEnabled());
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/autumn_tests.cpp

@@ -0,0 +1,600 @@
+// autumn_tests.cpp
+//
+// Autumn scene tests (architecture.md §16.5).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Persistence.h"
+#include "Sim.h"
+#include "snapshot_data.h"
+
+#include <algorithm>
+#include <array>
+#include <cmath>
+#include <filesystem>
+
+using namespace desktopgrass;
+
+namespace {
+
+constexpr double kMonitor1920 = 1920.0;
+constexpr double kEpsilon = 1e-9;
+constexpr double kTwoPi = 6.28318530717958647692;
+
+Sim make_sim(uint64_t seed = CANONICAL_TEST_SEED,
+             double width = kMonitor1920,
+             double density = DEFAULT_DENSITY) {
+    return sim_init(seed, width, density);
+}
+
+Sim make_autumn_sim(uint64_t seed = CANONICAL_TEST_SEED,
+                    double width = kMonitor1920,
+                    double density = DEFAULT_DENSITY) {
+    Sim sim = make_sim(seed, width, density);
+    sim_set_scene(sim, Scene::Autumn);
+    return sim;
+}
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+int count_maples(const Sim& sim) {
+    return static_cast<int>(std::count_if(sim.blades.begin(), sim.blades.end(),
+        [](const Blade& b) { return b.isMaple; }));
+}
+
+int count_new_leaf_spawns(Sim& sim, double seconds, double dt = 0.05) {
+    int count = 0;
+    const int steps = static_cast<int>(std::ceil(seconds / dt));
+    for (int i = 0; i < steps; ++i) {
+        sim_tick(sim, dt, nullptr, 0);
+        for (const Entity& e : sim.entities) {
+            if (e.kind == EntityKind::Leaf && e.age == Approx(0.0).margin(kEpsilon)) {
+                ++count;
+            }
+        }
+    }
+    return count;
+}
+
+const Entity& spawn_next_leaf(Sim& sim) {
+    const double dt = std::max(0.0, sim.nextLeafSpawnTime - sim.globalTime);
+    sim_tick(sim, dt, nullptr, 0);
+    auto it = std::find_if(sim.entities.rbegin(), sim.entities.rend(),
+        [](const Entity& e) { return e.kind == EntityKind::Leaf && e.age == Approx(0.0).margin(kEpsilon); });
+    REQUIRE(it != sim.entities.rend());
+    return *it;
+}
+
+const Blade* first_maple(const Sim& sim) {
+    auto it = std::find_if(sim.blades.begin(), sim.blades.end(),
+        [](const Blade& b) { return b.isMaple; });
+    return it == sim.blades.end() ? nullptr : &*it;
+}
+
+Sim make_autumn_sim_with_maple(uint64_t* outSeed = nullptr) {
+    for (uint64_t offset = 0; offset < 512; ++offset) {
+        const uint64_t seed = CANONICAL_TEST_SEED + offset;
+        Sim sim = make_autumn_sim(seed);
+        if (count_maples(sim) > 0) {
+            if (outSeed) *outSeed = seed;
+            return sim;
+        }
+    }
+    FAIL("Unable to find deterministic seed with a maple");
+    return make_autumn_sim();
+}
+
+// Find an Autumn sim that contains at least one leafy (non-bare) maple, and
+// return a pointer to it. The returned pointer is valid for the lifetime of
+// the returned-by-out sim.
+inline const Blade* first_leafy_maple(const Sim& sim) {
+    auto it = std::find_if(sim.blades.begin(), sim.blades.end(),
+        [](const Blade& b) { return b.isMaple && !b.mapleIsBare; });
+    return it == sim.blades.end() ? nullptr : &*it;
+}
+
+Sim make_autumn_sim_with_leafy_maple() {
+    for (uint64_t offset = 0; offset < 2048; ++offset) {
+        Sim sim = make_autumn_sim(CANONICAL_TEST_SEED + offset);
+        if (first_leafy_maple(sim) != nullptr) return sim;
+    }
+    FAIL("Unable to find deterministic seed with a leafy maple");
+    return make_autumn_sim();
+}
+
+std::filesystem::path autumn_state_path() {
+    std::filesystem::path dir = std::filesystem::current_path()
+        / ".copilot-scratch"
+        / "native-autumn-tests";
+    std::error_code ec;
+    std::filesystem::remove_all(dir, ec);
+    std::filesystem::create_directories(dir);
+    return dir / "state.json";
+}
+
+} // namespace
+
+TEST_CASE("Autumn scene count bumps to five", "[autumn][scene]") {
+    REQUIRE(SCENE_COUNT == 5);
+}
+
+TEST_CASE("Autumn scene enum value is pinned", "[autumn][scene]") {
+    REQUIRE(static_cast<int>(Scene::Autumn) == 3);
+}
+
+TEST_CASE("Autumn palette is pinned in scene palettes", "[autumn][palette]") {
+    for (int i = 0; i < PALETTE_SIZE; ++i) {
+        REQUIRE(SCENE_PALETTES[static_cast<int>(Scene::Autumn)][i] == AUTUMN_PALETTE[i]);
+    }
+}
+
+TEST_CASE("Autumn does not change default scene", "[autumn][scene]") {
+    REQUIRE(SCENE_DEFAULT == Scene::Grass);
+}
+
+TEST_CASE("Leaf constants match Autumn spec", "[autumn][leaf][constants]") {
+    REQUIRE(LEAF_SPAWN_RATE_PER_SEC_1920DIP == Approx(1.4));
+    REQUIRE(LEAF_FALL_SPEED_MIN == Approx(14.0));
+    REQUIRE(LEAF_FALL_SPEED_MAX == Approx(26.0));
+    REQUIRE(LEAF_HORIZONTAL_DRIFT_AMP == Approx(32.0));
+    REQUIRE(LEAF_HORIZONTAL_DRIFT_FREQ == Approx(1.4));
+    REQUIRE(LEAF_ROTATION_SPEED_MIN == Approx(0.8));
+    REQUIRE(LEAF_ROTATION_SPEED_MAX == Approx(2.4));
+    REQUIRE(LEAF_SIZE_MIN == Approx(4.0));
+    REQUIRE(LEAF_SIZE_MAX == Approx(7.0));
+    REQUIRE(LEAF_SPAWN_Y_OFFSET == Approx(-10.0));
+    REQUIRE(LEAF_COLOR_COUNT == 6);
+    constexpr uint32_t expected[LEAF_COLOR_COUNT] = {
+        0xFFD96B0Cu, 0xFFB54D1Eu, 0xFFE89A3Cu,
+        0xFFC23E12u, 0xFFE6C849u, 0xFF8C2E0Fu,
+    };
+    for (int i = 0; i < LEAF_COLOR_COUNT; ++i) {
+        REQUIRE(LEAF_COLORS[i] == expected[i]);
+    }
+    REQUIRE(LEAF_PRNG_SALT == 0x1EA1DEC1D1EA1D05ull);
+}
+
+TEST_CASE("Autumn leaf spawn rate is gated and near mean", "[autumn][leaf]") {
+    Sim autumn = make_autumn_sim();
+    const int count = count_new_leaf_spawns(autumn, 100.0);
+    REQUIRE(count >= 112);
+    REQUIRE(count <= 168);
+}
+
+TEST_CASE("Only Autumn spawns leaves", "[autumn][leaf][gating]") {
+    for (Scene scene : { Scene::Grass, Scene::Desert, Scene::Winter }) {
+        Sim sim = make_sim();
+        sim_set_scene(sim, scene);
+        count_new_leaf_spawns(sim, 30.0);
+        REQUIRE(count_kind(sim, EntityKind::Leaf) == 0);
+    }
+}
+
+TEST_CASE("Leaf fall speed stays within pinned range", "[autumn][leaf]") {
+    Sim sim = make_autumn_sim();
+    for (int i = 0; i < 32; ++i) {
+        const Entity& e = spawn_next_leaf(sim);
+        REQUIRE(e.vy >= LEAF_FALL_SPEED_MIN);
+        REQUIRE(e.vy <= LEAF_FALL_SPEED_MAX);
+        REQUIRE(e.baseSpeed == Approx(e.vy));
+    }
+}
+
+TEST_CASE("Leaf size stays within pinned range", "[autumn][leaf]") {
+    Sim sim = make_autumn_sim();
+    for (int i = 0; i < 32; ++i) {
+        const Entity& e = spawn_next_leaf(sim);
+        REQUIRE(e.size >= LEAF_SIZE_MIN);
+        REQUIRE(e.size <= LEAF_SIZE_MAX);
+    }
+}
+
+TEST_CASE("Leaf color variant stays within pinned range", "[autumn][leaf]") {
+    Sim sim = make_autumn_sim();
+    for (int i = 0; i < 32; ++i) {
+        const Entity& e = spawn_next_leaf(sim);
+        REQUIRE(e.colorVariant < LEAF_COLOR_COUNT);
+    }
+}
+
+TEST_CASE("Leaf PRNG draw order matches side stream", "[autumn][leaf][prng]") {
+    Sim sim = make_autumn_sim();
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ LEAF_PRNG_SALT);
+    const double lambda = LEAF_SPAWN_RATE_PER_SEC_1920DIP * sim.monitorWidth / 1920.0;
+    double expectedNext = 0.0;
+
+    for (int i = 0; i < 8; ++i) {
+        const Entity& e = spawn_next_leaf(sim);
+        const double xFrac = prng_uniform(side, 0.0, 1.0);
+        const double expectedSpawnX = xFrac * sim.monitorWidth;
+        const double expectedFallSpeed = prng_uniform(side, LEAF_FALL_SPEED_MIN, LEAF_FALL_SPEED_MAX);
+        const double expectedPhase = prng_uniform(side, 0.0, kTwoPi);
+        const double rotationMag = prng_uniform(side, LEAF_ROTATION_SPEED_MIN, LEAF_ROTATION_SPEED_MAX);
+        const double rotationSign = (prng_next_u64(side) & 1ull) != 0ull ? 1.0 : -1.0;
+        const double expectedRotation = prng_uniform(side, 0.0, kTwoPi);
+        const double expectedSize = prng_uniform(side, LEAF_SIZE_MIN, LEAF_SIZE_MAX);
+        const uint8_t expectedColor = static_cast<uint8_t>(prng_index(side, LEAF_COLOR_COUNT));
+        expectedNext += prng_exponential(side, lambda);
+
+        REQUIRE(e.x0 == Approx(expectedSpawnX).margin(kEpsilon));
+        REQUIRE(e.x == Approx(expectedSpawnX + LEAF_HORIZONTAL_DRIFT_AMP * std::sin(expectedPhase)).margin(kEpsilon));
+        REQUIRE(e.vy == Approx(expectedFallSpeed).margin(kEpsilon));
+        REQUIRE(e.phaseX == Approx(expectedPhase).margin(kEpsilon));
+        REQUIRE(e.rotationSpeed == Approx(rotationMag * rotationSign).margin(kEpsilon));
+        REQUIRE(e.rotation == Approx(expectedRotation).margin(kEpsilon));
+        REQUIRE(e.size == Approx(expectedSize).margin(kEpsilon));
+        REQUIRE(e.colorVariant == expectedColor);
+        REQUIRE(sim.nextLeafSpawnTime == Approx(expectedNext).margin(kEpsilon));
+    }
+}
+
+TEST_CASE("Leaf despawns when past ground", "[autumn][leaf]") {
+    Sim sim = make_autumn_sim();
+    Entity e{};
+    e.kind = EntityKind::Leaf;
+    e.y = sim.windowHeight + 0.1;
+    e.lifetime = -1.0;
+    sim.entities.push_back(e);
+    sim.nextLeafSpawnTime = 1.0e9;
+    sim_tick_entities(sim, 0.0);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) == 0);
+}
+
+TEST_CASE("Leaf ignores click-cut interaction", "[autumn][leaf]") {
+    Sim sim = make_autumn_sim();
+    Entity e{};
+    e.kind = EntityKind::Leaf;
+    e.x = 200.0;
+    e.y = sim.windowHeight - 5.0;
+    e.size = 5.0;
+    e.lifetime = -1.0;
+    sim.entities.push_back(e);
+
+    InputEvent click{};
+    click.type = EventType::Click;
+    click.x = e.x;
+    click.y = e.y;
+    click.time = sim.globalTime;
+    sim_apply_click(sim, click);
+
+    REQUIRE(count_kind(sim, EntityKind::Leaf) == 1);
+}
+
+TEST_CASE("Leaf EntityKind value is pinned", "[autumn][leaf][enum]") {
+    REQUIRE(static_cast<int>(EntityKind::Leaf) == 11);
+}
+
+TEST_CASE("Maple constants match Autumn spec", "[autumn][maple][constants]") {
+    REQUIRE(MAPLE_PROBABILITY == Approx(0.0070));
+    REQUIRE(MAPLE_HEIGHT_MIN == Approx(50.0));
+    REQUIRE(MAPLE_HEIGHT_MAX == Approx(85.0));
+    REQUIRE(MAPLE_TRUNK_WIDTH_MIN == Approx(6.0));
+    REQUIRE(MAPLE_TRUNK_WIDTH_MAX == Approx(10.0));
+    REQUIRE(MAPLE_CANOPY_RADIUS_MIN == Approx(14.0));
+    REQUIRE(MAPLE_CANOPY_RADIUS_MAX == Approx(24.0));
+    REQUIRE(MAPLE_TRUNK_COLOR == 0xFF4A2C18u);
+    REQUIRE(MAPLE_TRUNK_DARK == 0xFF2F1B0Eu);
+    REQUIRE(MAPLE_CANOPY_COLOR_COUNT == 4);
+    constexpr uint32_t expected[MAPLE_CANOPY_COLOR_COUNT] = {
+        0xFFD96B0Cu, 0xFFE89A3Cu, 0xFFC23E12u, 0xFFE6C849u,
+    };
+    for (int i = 0; i < MAPLE_CANOPY_COLOR_COUNT; ++i) {
+        REQUIRE(MAPLE_CANOPY_COLORS[i] == expected[i]);
+    }
+    REQUIRE(MAPLE_BARE_FRACTION == Approx(0.20));
+    REQUIRE(MAPLE_PRNG_SALT == 0xC1AA51EC1AA51Eull);
+}
+
+TEST_CASE("Maples generate only in Autumn", "[autumn][maple][gating]") {
+    for (Scene scene : { Scene::Grass, Scene::Desert, Scene::Winter }) {
+        Sim sim = make_sim();
+        sim_set_scene(sim, scene);
+        REQUIRE(count_maples(sim) == 0);
+    }
+    REQUIRE(count_maples(make_autumn_sim_with_maple()) > 0);
+}
+
+TEST_CASE("Maple promotion probability is near spec", "[autumn][maple]") {
+    int totalSlots = 0;
+    int totalMaples = 0;
+    for (uint64_t seed = CANONICAL_TEST_SEED; seed < CANONICAL_TEST_SEED + 200; ++seed) {
+        Sim sim = make_autumn_sim(seed);
+        totalSlots += static_cast<int>(sim.blades.size());
+        totalMaples += count_maples(sim);
+    }
+    const double fraction = static_cast<double>(totalMaples) / static_cast<double>(totalSlots);
+    REQUIRE(fraction >= MAPLE_PROBABILITY * 0.75);
+    REQUIRE(fraction <= MAPLE_PROBABILITY * 1.25);
+}
+
+TEST_CASE("Maple height stays within pinned range", "[autumn][maple]") {
+    Sim sim = make_autumn_sim_with_maple();
+    for (const Blade& b : sim.blades) if (b.isMaple) {
+        REQUIRE(b.mapleHeight >= MAPLE_HEIGHT_MIN);
+        REQUIRE(b.mapleHeight <= MAPLE_HEIGHT_MAX);
+    }
+}
+
+TEST_CASE("Maple trunk width stays within pinned range", "[autumn][maple]") {
+    Sim sim = make_autumn_sim_with_maple();
+    for (const Blade& b : sim.blades) if (b.isMaple) {
+        REQUIRE(b.mapleTrunkWidth >= MAPLE_TRUNK_WIDTH_MIN);
+        REQUIRE(b.mapleTrunkWidth <= MAPLE_TRUNK_WIDTH_MAX);
+    }
+}
+
+TEST_CASE("Maple canopy radius stays within pinned range", "[autumn][maple]") {
+    Sim sim = make_autumn_sim_with_maple();
+    for (const Blade& b : sim.blades) if (b.isMaple) {
+        REQUIRE(b.mapleCanopyRadius >= MAPLE_CANOPY_RADIUS_MIN);
+        REQUIRE(b.mapleCanopyRadius <= MAPLE_CANOPY_RADIUS_MAX);
+    }
+}
+
+TEST_CASE("Maple canopy color variant stays within pinned range", "[autumn][maple]") {
+    Sim sim = make_autumn_sim_with_maple();
+    for (const Blade& b : sim.blades) if (b.isMaple) {
+        REQUIRE(b.mapleCanopyColorIdx < MAPLE_CANOPY_COLOR_COUNT);
+    }
+}
+
+TEST_CASE("Maple bare fraction is near spec", "[autumn][maple]") {
+    int totalMaples = 0;
+    int totalBare = 0;
+    for (uint64_t seed = CANONICAL_TEST_SEED; seed < CANONICAL_TEST_SEED + 400; ++seed) {
+        Sim sim = make_autumn_sim(seed);
+        for (const Blade& b : sim.blades) if (b.isMaple) {
+            ++totalMaples;
+            if (b.mapleIsBare) ++totalBare;
+        }
+    }
+    REQUIRE(totalMaples > 100);
+    const double fraction = static_cast<double>(totalBare) / static_cast<double>(totalMaples);
+    REQUIRE(fraction >= MAPLE_BARE_FRACTION - 0.05);
+    REQUIRE(fraction <= MAPLE_BARE_FRACTION + 0.05);
+}
+
+TEST_CASE("Maple PRNG draw order matches side stream", "[autumn][maple][prng]") {
+    uint64_t seed = 0;
+    Sim sim = make_autumn_sim_with_maple(&seed);
+    Prng side;
+    prng_init(side, seed ^ MAPLE_PRNG_SALT);
+
+    for (std::size_t i = 0; i < sim.blades.size(); ++i) {
+        const double r = prng_uniform(side, 0.0, 1.0);
+        if (r >= MAPLE_PROBABILITY) {
+            REQUIRE_FALSE(sim.blades[i].isMaple);
+            continue;
+        }
+
+        const double expectedHeight = prng_uniform(side, MAPLE_HEIGHT_MIN, MAPLE_HEIGHT_MAX);
+        const double expectedTrunkWidth = prng_uniform(side, MAPLE_TRUNK_WIDTH_MIN, MAPLE_TRUNK_WIDTH_MAX);
+        const double expectedCanopyRadius = prng_uniform(side, MAPLE_CANOPY_RADIUS_MIN, MAPLE_CANOPY_RADIUS_MAX);
+        const uint8_t expectedColor = static_cast<uint8_t>(prng_index(side, MAPLE_CANOPY_COLOR_COUNT));
+        const bool expectedBare = prng_uniform(side, 0.0, 1.0) < MAPLE_BARE_FRACTION;
+
+        const Blade& b = sim.blades[i];
+        REQUIRE(b.isMaple);
+        REQUIRE(b.mapleHeight == Approx(expectedHeight).margin(kEpsilon));
+        REQUIRE(b.mapleTrunkWidth == Approx(expectedTrunkWidth).margin(kEpsilon));
+        REQUIRE(b.mapleCanopyRadius == Approx(expectedCanopyRadius).margin(kEpsilon));
+        REQUIRE(b.mapleCanopyColorIdx == expectedColor);
+        REQUIRE(b.mapleIsBare == expectedBare);
+        return;
+    }
+    FAIL("Expected a maple promotion");
+}
+
+TEST_CASE("Maples are cuttable through existing cut model", "[autumn][maple]") {
+    Sim sim = make_autumn_sim_with_maple();
+    const Blade* maple = first_maple(sim);
+    REQUIRE(maple != nullptr);
+    const double clickX = maple->baseX;
+
+    InputEvent click{};
+    click.type = EventType::Click;
+    click.x = clickX;
+    click.y = sim.windowHeight - 1.0;
+    click.time = sim.globalTime;
+    sim_apply_click(sim, click);
+    sim_tick(sim, CUT_DURATION_SEC + 0.01, nullptr, 0);
+
+    const Blade& cutMaple = *std::find_if(sim.blades.begin(), sim.blades.end(),
+        [clickX](const Blade& b) { return b.isMaple && b.baseX == Approx(clickX); });
+    // Cut blades now settle at their per-blade stubble floor, not flat zero.
+    REQUIRE(cutMaple.cutFloor > 0.0);
+    REQUIRE(cutMaple.cutHeight == Approx(cutMaple.cutFloor).margin(kEpsilon));
+}
+
+TEST_CASE("Autumn is critter-free", "[autumn][critter][gating]") {
+    Sim sim = make_autumn_sim();
+    REQUIRE(count_kind(sim, EntityKind::Sheep) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Hedgehog) == 0);
+}
+
+
+TEST_CASE("Autumn does not spawn snowflakes", "[autumn][weather]") {
+    Sim sim = make_autumn_sim();
+    for (int i = 0; i < 500; ++i) sim_tick(sim, 0.05, nullptr, 0);
+    REQUIRE(count_kind(sim, EntityKind::Snowflake) == 0);
+}
+
+TEST_CASE("Autumn scene persists round-trip", "[autumn][persistence]") {
+    const auto path = autumn_state_path();
+    persistence::SetStateFilePathForTest(path.wstring());
+
+    persistence::AppState expected;
+    expected.scene = Scene::Autumn;
+    REQUIRE(persistence::SaveAppState(expected));
+
+    persistence::AppState actual;
+    REQUIRE(persistence::LoadAppState(actual));
+    REQUIRE(actual.scene == Scene::Autumn);
+}
+
+TEST_CASE("Leaf puff constants are pinned", "[autumn][leaf][puff][constants]") {
+    REQUIRE(LEAF_PUFF_COUNT_MIN == 4);
+    REQUIRE(LEAF_PUFF_COUNT_MAX == 7);
+    REQUIRE(LEAF_PUFF_BURST_SPEED_MIN == Approx(18.0));
+    REQUIRE(LEAF_PUFF_BURST_SPEED_MAX == Approx(42.0));
+    REQUIRE(LEAF_PUFF_DRAG == Approx(2.2));
+    REQUIRE(LEAF_PUFF_COOLDOWN_SEC == Approx(1.5));
+    REQUIRE(LEAF_PUFF_HOVER_RADIUS_MUL == Approx(1.15));
+    REQUIRE(LEAF_PUFF_MIN_CUT_HEIGHT == Approx(0.5));
+    REQUIRE(LEAF_PUFF_START_OFFSET_FRAC == Approx(0.4));
+}
+
+TEST_CASE("Hovering a leafy maple sheds a leaf puff", "[autumn][leaf][puff]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    REQUIRE(maple != nullptr);
+    const double cx = maple->baseX;
+    const double cy = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+
+    const int before = count_kind(sim, EntityKind::Leaf);
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = cx;
+    mv.y = cy;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+
+    const int puffed = count_kind(sim, EntityKind::Leaf) - before;
+    REQUIRE(puffed >= LEAF_PUFF_COUNT_MIN);
+    REQUIRE(puffed <= LEAF_PUFF_COUNT_MAX);
+
+    const bool anyBurst = std::any_of(sim.entities.begin(), sim.entities.end(),
+        [](const Entity& e) { return e.kind == EntityKind::Leaf && e.vx != 0.0; });
+    REQUIRE(anyBurst);
+}
+
+TEST_CASE("Leaf puff respects a per-tree cooldown", "[autumn][leaf][puff]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    const double cx = maple->baseX;
+    const double cy = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = cx;
+    mv.y = cy;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    const int afterFirst = count_kind(sim, EntityKind::Leaf);
+    REQUIRE(afterFirst > 0);
+
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) == afterFirst);
+
+    sim.globalTime += LEAF_PUFF_COOLDOWN_SEC + 0.1;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) > afterFirst);
+}
+
+TEST_CASE("Leaf puff ignores cursor away from canopy", "[autumn][leaf][puff]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    const int before = count_kind(sim, EntityKind::Leaf);
+
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = maple->baseX + 400.0;
+    mv.y = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) == before);
+}
+
+TEST_CASE("Leaf puff does not fire outside Autumn", "[autumn][leaf][puff][gating]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    const double cx = maple->baseX;
+    const double cy = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+    sim.currentScene = Scene::Grass;
+
+    const int before = count_kind(sim, EntityKind::Leaf);
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = cx;
+    mv.y = cy;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) == before);
+}
+
+TEST_CASE("Puff burst decays so leaves settle into flutter", "[autumn][leaf][puff]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = maple->baseX;
+    mv.y = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) > 0);
+
+    for (int i = 0; i < 40; ++i) sim_tick(sim, 0.05, nullptr, 0);
+    for (const Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Leaf) REQUIRE(e.vx == Approx(0.0).margin(kEpsilon));
+    }
+}
+
+TEST_CASE("Re-entering Autumn clears the puff cooldown", "[autumn][leaf][puff]") {
+    Sim sim = make_autumn_sim_with_leafy_maple();
+    const Blade* maple = first_leafy_maple(sim);
+    InputEvent mv{};
+    mv.type = EventType::Move;
+    mv.x = maple->baseX;
+    mv.y = sim.windowHeight - maple->mapleHeight * maple->cutHeight;
+    mv.time = sim.globalTime;
+    sim_apply_move(sim, mv);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) > 0);
+
+    // Leaving and re-entering Autumn regenerates the (deterministic) maples and
+    // must reset their puff cooldown so the fresh scene can puff immediately.
+    sim_set_scene(sim, Scene::Grass);
+    sim_set_scene(sim, Scene::Autumn);
+    const Blade* maple2 = first_leafy_maple(sim);
+    REQUIRE(maple2 != nullptr);
+
+    const int before = count_kind(sim, EntityKind::Leaf);
+    InputEvent mv2{};
+    mv2.type = EventType::Move;
+    mv2.x = maple2->baseX;
+    mv2.y = sim.windowHeight - maple2->mapleHeight * maple2->cutHeight;
+    mv2.time = sim.globalTime;
+    sim_apply_move(sim, mv2);
+    REQUIRE(count_kind(sim, EntityKind::Leaf) > before);
+}
+
+TEST_CASE("Autumn PRNG salts are unique", "[autumn][prng]") {
+    constexpr std::array<uint64_t, 16> salts = {
+        REGROW_PRNG_SALT,
+        FLOWER_PRNG_SALT,
+        MUSHROOM_PRNG_SALT,
+        AMBIENT_GUST_PRNG_SALT,
+        CACTUS_PRNG_SALT,
+        TUMBLEWEED_PRNG_SALT,
+        CRITTER_PRNG_SALT,
+        BUTTERFLY_PRNG_SALT,
+        FIREFLY_PRNG_SALT,
+        BIRD_FLYBY_PRNG_SALT,
+        SNOWFLAKE_PRNG_SALT,
+        PINE_PRNG_SALT,
+        LEAF_PRNG_SALT,
+        MAPLE_PRNG_SALT,
+        LEAF_PUFF_PRNG_SALT,
+    };
+
+    for (std::size_t i = 0; i < salts.size(); ++i) {
+        for (std::size_t j = i + 1; j < salts.size(); ++j) {
+            REQUIRE(salts[i] != salts[j]);
+        }
+    }
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/bird_flyby_tests.cpp

@@ -0,0 +1,365 @@
+// bird_flyby_tests.cpp - §17.8 ambient bird flyby tests.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+
+namespace {
+constexpr double Monitor1920 = 1920.0;
+constexpr double TwoPi = 6.28318530717958647692;
+
+Sim build_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    Sim sim = sim_init(seed, Monitor1920, DEFAULT_DENSITY);
+    sim.currentScene = Scene::Grass;
+    sim.entities.clear();
+    return sim;
+}
+
+int count_birds(const Sim& sim) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [](const Entity& e) { return e.kind == EntityKind::Bird; }));
+}
+
+std::vector<Entity> birds(const Sim& sim) {
+    std::vector<Entity> out;
+    for (const Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Bird) out.push_back(e);
+    }
+    return out;
+}
+
+int prng_count(Prng& side, int minCount, int maxCount) {
+    const double draw = prng_uniform(side, static_cast<double>(minCount), static_cast<double>(maxCount + 1));
+    int count = static_cast<int>(std::floor(draw));
+    if (count < minCount) count = minCount;
+    if (count > maxCount) count = maxCount;
+    return count;
+}
+
+void reset_bird_stream_fresh(Sim& sim, uint64_t seed) {
+    prng_init(sim.birdFlybyPrng, seed ^ BIRD_FLYBY_PRNG_SALT);
+    sim.nextBirdFlybyAtTime = sim.globalTime;
+}
+
+void reset_bird_schedule(Sim& sim, uint64_t seed) {
+    prng_init(sim.birdFlybyPrng, seed ^ BIRD_FLYBY_PRNG_SALT);
+    sim.nextBirdFlybyAtTime = sim.globalTime + bird_flyby_sample_interval(sim.birdFlybyPrng);
+}
+
+uint64_t find_seed_for_flock_size(int size) {
+    for (uint64_t i = 1; i < 10000; ++i) {
+        Sim sim = build_sim(CANONICAL_TEST_SEED + i);
+        reset_bird_stream_fresh(sim, CANONICAL_TEST_SEED + i);
+        sim_spawn_bird_flyby(sim);
+        if (count_birds(sim) == size) return CANONICAL_TEST_SEED + i;
+    }
+    return CANONICAL_TEST_SEED;
+}
+
+uint64_t find_v_seed(int minSize) {
+    for (uint64_t i = 1; i < 10000; ++i) {
+        Sim sim = build_sim(CANONICAL_TEST_SEED + i);
+        reset_bird_stream_fresh(sim, CANONICAL_TEST_SEED + i);
+        sim_spawn_bird_flyby(sim);
+        auto flock = birds(sim);
+        if (static_cast<int>(flock.size()) >= minSize && flock[0].colorVariant == 0) {
+            return CANONICAL_TEST_SEED + i;
+        }
+    }
+    return CANONICAL_TEST_SEED;
+}
+} // namespace
+
+TEST_CASE("Bird flyby constants are pinned to spec values", "[bird][constants]") {
+    REQUIRE(BIRD_FLYBY_SPAWN_RATE_PER_HOUR == Approx(15.0));
+    REQUIRE(BIRD_FLOCK_SIZE_MIN == 3);
+    REQUIRE(BIRD_FLOCK_SIZE_MAX == 7);
+    REQUIRE(BIRD_FLOCK_FORMATION_SPACING == Approx(9.0));
+    REQUIRE(BIRD_FLOCK_V_ANGLE_DEG == Approx(22.0));
+    REQUIRE(BIRD_SPEED_MIN == Approx(65.0));
+    REQUIRE(BIRD_SPEED_MAX == Approx(95.0));
+    REQUIRE(BIRD_ALTITUDE_MIN == Approx(78.0));
+    REQUIRE(BIRD_ALTITUDE_MAX == Approx(96.0));
+    REQUIRE(BIRD_BODY_LENGTH == Approx(3.6));
+    REQUIRE(BIRD_WING_SPAN == Approx(5.0));
+    REQUIRE(BIRD_WING_FLAP_FREQ == Approx(7.0));
+    REQUIRE(BIRD_WING_FLAP_PHASE_JITTER == Approx(0.6));
+    REQUIRE(BIRD_BODY_COLOR == 0xFF1A1610u);
+    REQUIRE(BIRD_WING_OPEN_RATIO == Approx(1.0));
+    REQUIRE(BIRD_WING_FOLD_RATIO == Approx(0.30));
+    REQUIRE(BIRD_FADE_IN_FRAC == Approx(0.08));
+    REQUIRE(BIRD_FADE_OUT_FRAC == Approx(0.08));
+    REQUIRE(BIRD_DRIFT_AMP_Y == Approx(3.0));
+    REQUIRE(BIRD_DRIFT_FREQ_Y == Approx(0.8));
+    REQUIRE(BIRD_FLYBY_PRNG_SALT == 0xB12D1F1A1B12D1Aull);
+}
+
+TEST_CASE("Bird flyby PRNG salt is unique", "[bird][constants]") {
+    const uint64_t salts[] = {
+        REGROW_PRNG_SALT, FLOWER_PRNG_SALT, MUSHROOM_PRNG_SALT,
+        AMBIENT_GUST_PRNG_SALT, CACTUS_PRNG_SALT, TUMBLEWEED_PRNG_SALT,
+        CRITTER_PRNG_SALT, BUTTERFLY_PRNG_SALT, FIREFLY_PRNG_SALT,
+        SNOWFLAKE_PRNG_SALT, PINE_PRNG_SALT,
+    };
+    for (uint64_t salt : salts) {
+        REQUIRE(BIRD_FLYBY_PRNG_SALT != salt);
+    }
+}
+
+TEST_CASE("Bird flyby flock size stays in range over seeds", "[bird][spawn]") {
+    for (uint64_t i = 0; i < 256; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = build_sim(seed);
+        reset_bird_stream_fresh(sim, seed);
+        sim_spawn_bird_flyby(sim);
+        REQUIRE(count_birds(sim) >= BIRD_FLOCK_SIZE_MIN);
+        REQUIRE(count_birds(sim) <= BIRD_FLOCK_SIZE_MAX);
+    }
+}
+
+TEST_CASE("Bird flyby leader altitude stays in range", "[bird][spawn]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i;
+        Sim sim = build_sim(seed);
+        reset_bird_stream_fresh(sim, seed);
+        sim_spawn_bird_flyby(sim);
+        auto flock = birds(sim);
+        REQUIRE(!flock.empty());
+        REQUIRE(flock[0].altitudeAnchor >= BIRD_ALTITUDE_MIN);
+        REQUIRE(flock[0].altitudeAnchor <  BIRD_ALTITUDE_MAX);
+    }
+}
+
+TEST_CASE("Bird flyby leader speed stays in range", "[bird][spawn]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i;
+        Sim sim = build_sim(seed);
+        reset_bird_stream_fresh(sim, seed);
+        sim_spawn_bird_flyby(sim);
+        auto flock = birds(sim);
+        REQUIRE(!flock.empty());
+        REQUIRE(flock[0].baseSpeed >= BIRD_SPEED_MIN);
+        REQUIRE(flock[0].baseSpeed <  BIRD_SPEED_MAX);
+        REQUIRE(std::abs(flock[0].vx) == Approx(flock[0].baseSpeed));
+    }
+}
+
+TEST_CASE("Bird flyby PRNG draw order matches side stream", "[bird][prng]") {
+    const uint64_t seed = 0xB17D5EED1234ull;
+    Sim sim = build_sim(seed);
+    reset_bird_stream_fresh(sim, seed);
+    Prng side;
+    prng_init(side, seed ^ BIRD_FLYBY_PRNG_SALT);
+
+    sim_spawn_bird_flyby(sim);
+    const int expectedCount = prng_count(side, BIRD_FLOCK_SIZE_MIN, BIRD_FLOCK_SIZE_MAX);
+    const uint64_t directionBit = prng_next_u64(side) & 1ull;
+    const double direction = directionBit != 0ull ? 1.0 : -1.0;
+    const double leaderAltitude = prng_uniform(side, BIRD_ALTITUDE_MIN, BIRD_ALTITUDE_MAX);
+    const double leaderSpeed = prng_uniform(side, BIRD_SPEED_MIN, BIRD_SPEED_MAX);
+    const uint64_t formationStyle = prng_next_u64(side) & 1ull;
+
+    std::vector<double> wingPhases;
+    std::vector<double> driftPhases;
+    for (int i = 0; i < expectedCount; ++i) {
+        wingPhases.push_back(prng_uniform(side, -BIRD_WING_FLAP_PHASE_JITTER, BIRD_WING_FLAP_PHASE_JITTER));
+        driftPhases.push_back(prng_uniform(side, 0.0, TwoPi));
+    }
+
+    auto flock = birds(sim);
+    REQUIRE(static_cast<int>(flock.size()) == expectedCount);
+    REQUIRE(sim.birdFlybyPrng.state == side.state);
+
+    const double spawnX = direction > 0.0 ? -50.0 : Monitor1920 + 50.0;
+    const double sinAngle = std::sin(BIRD_FLOCK_V_ANGLE_DEG * 3.14159265358979323846 / 180.0);
+    for (int i = 0; i < expectedCount; ++i) {
+        const double along = -static_cast<double>(i) * BIRD_FLOCK_FORMATION_SPACING;
+        double perpendicular = 0.0;
+        if (formationStyle == 0ull) {
+            const int armIndex = (i + 1) / 2;
+            const double sideSign = (i % 2) == 0 ? 1.0 : -1.0;
+            perpendicular = sideSign * static_cast<double>(armIndex) * BIRD_FLOCK_FORMATION_SPACING * sinAngle;
+        } else {
+            perpendicular = static_cast<double>(i) * BIRD_FLOCK_FORMATION_SPACING * sinAngle;
+        }
+
+        const Entity& e = flock[static_cast<std::size_t>(i)];
+        REQUIRE(e.x0 == Approx(spawnX + direction * along));
+        REQUIRE(e.x == Approx(e.x0));
+        REQUIRE(e.vx == Approx(direction * leaderSpeed));
+        REQUIRE(e.baseSpeed == Approx(leaderSpeed));
+        REQUIRE(e.altitudeAnchor == Approx(leaderAltitude - perpendicular));
+        REQUIRE(e.phaseX == Approx(wingPhases[static_cast<std::size_t>(i)]));
+        REQUIRE(e.phaseY == Approx(driftPhases[static_cast<std::size_t>(i)]));
+        REQUIRE(e.formationOffsetAlongFlight == Approx(along));
+        REQUIRE(e.formationOffsetPerpendicular == Approx(perpendicular));
+        REQUIRE(e.colorVariant == static_cast<uint8_t>(formationStyle));
+        REQUIRE(e.spawnTime == Approx(sim.globalTime));
+    }
+}
+
+TEST_CASE("Bird flybys are Grass scene only", "[bird][scene]") {
+    for (Scene scene : { Scene::Desert, Scene::Winter }) {
+        Sim sim = build_sim();
+        sim_set_scene(sim, scene);
+        sim.entities.clear();
+        reset_bird_schedule(sim, CANONICAL_TEST_SEED);
+        for (int i = 0; i < 8 * 3600; ++i) {
+            sim.globalTime += 1.0;
+            sim_tick_bird_flybys(sim);
+        }
+        REQUIRE(count_birds(sim) == 0);
+    }
+}
+
+TEST_CASE("Bird flyby Poisson spawns when schedule elapses", "[bird][time]") {
+    Sim sim = build_sim(0xDAD1B17Dull);
+    reset_bird_schedule(sim, 0xDAD1B17Dull);
+    int flybys = 0;
+    for (int i = 0; i < 10 * 3600; ++i) {
+        sim.globalTime += 1.0;
+        const int before = count_birds(sim);
+        sim_tick_bird_flybys(sim);
+        if (count_birds(sim) > before) {
+            ++flybys;
+            sim.entities.clear();
+        }
+    }
+
+    const double observedPerHour = static_cast<double>(flybys) / 10.0;
+    REQUIRE(observedPerHour == Approx(BIRD_FLYBY_SPAWN_RATE_PER_HOUR).epsilon(0.15));
+}
+
+TEST_CASE("Bird V formation geometry is locked", "[bird][formation]") {
+    const uint64_t seed = find_v_seed(5);
+    Sim sim = build_sim(seed);
+    reset_bird_stream_fresh(sim, seed);
+    sim_spawn_bird_flyby(sim);
+    auto flock = birds(sim);
+    REQUIRE(flock.size() >= 5);
+    REQUIRE(flock[0].colorVariant == 0);
+    REQUIRE(flock[0].formationOffsetAlongFlight == Approx(0.0));
+
+    for (std::size_t i = 1; i < flock.size(); ++i) {
+        REQUIRE(std::fabs(flock[0].formationOffsetAlongFlight)
+            < std::fabs(flock[i].formationOffsetAlongFlight));
+        REQUIRE(flock[i - 1].formationOffsetAlongFlight - flock[i].formationOffsetAlongFlight
+            == Approx(BIRD_FLOCK_FORMATION_SPACING));
+        const double expectedSign = (i % 2 == 0) ? 1.0 : -1.0;
+        REQUIRE((flock[i].formationOffsetPerpendicular > 0.0 ? 1.0 : -1.0) == expectedSign);
+    }
+}
+
+TEST_CASE("Bird wing flap scale stays in range", "[bird][wing]") {
+    for (int i = 0; i < 200; ++i) {
+        const double t = i * 0.137;
+        const double phase = -BIRD_WING_FLAP_PHASE_JITTER
+            + (2.0 * BIRD_WING_FLAP_PHASE_JITTER) * (static_cast<double>(i) / 199.0);
+        const double scale = bird_wing_scale(t, phase);
+        REQUIRE(scale >= BIRD_WING_FOLD_RATIO);
+        REQUIRE(scale <= BIRD_WING_OPEN_RATIO);
+    }
+}
+
+TEST_CASE("Bird wing phases decorrelate within a flock", "[bird][wing]") {
+    for (uint64_t i = 1; i < 10000; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i;
+        Sim sim = build_sim(seed);
+        reset_bird_stream_fresh(sim, seed);
+        sim_spawn_bird_flyby(sim);
+        auto flock = birds(sim);
+        if (flock.size() != 5) continue;
+
+        std::vector<double> distinct;
+        for (const Entity& e : flock) {
+            const double scale = bird_wing_scale(1.234, e.phaseX);
+            bool seen = false;
+            for (double existing : distinct) {
+                if (std::fabs(existing - scale) < 1e-6) { seen = true; break; }
+            }
+            if (!seen) distinct.push_back(scale);
+        }
+        if (distinct.size() >= 3) {
+            REQUIRE(distinct.size() >= 3);
+            return;
+        }
+    }
+    FAIL("no decorrelated 5-bird flock found");
+}
+
+TEST_CASE("Birds despawn past opposite boundary", "[bird][despawn]") {
+    Sim sim = build_sim();
+    sim.currentScene = Scene::Desert;
+    sim.entities.clear();
+    Entity bird{};
+    bird.kind = EntityKind::Bird;
+    bird.x = Monitor1920 + 49.0;
+    bird.y = 10.0;
+    bird.vx = 20.0;
+    bird.altitudeAnchor = BIRD_ALTITUDE_MIN;
+    bird.lifetime = -1.0;
+    sim.entities.push_back(bird);
+
+    sim_tick_entities(sim, 0.2);
+
+    REQUIRE(count_birds(sim) == 0);
+}
+
+TEST_CASE("Birds do not interact with cuts or critters", "[bird][interaction]") {
+    Sim sim = build_sim();
+    sim.entities.clear();
+    Entity bird{};
+    bird.kind = EntityKind::Bird;
+    bird.x = 500.0;
+    bird.y = sim.windowHeight - STRIP_HEIGHT - 10.0;
+    bird.vx = BIRD_SPEED_MIN;
+    bird.baseSpeed = BIRD_SPEED_MIN;
+    bird.altitudeAnchor = BIRD_ALTITUDE_MIN;
+    bird.lifetime = -1.0;
+    sim.entities.push_back(bird);
+
+    Entity sheep{};
+    sheep.kind = EntityKind::Sheep;
+    sheep.x = bird.x;
+    sheep.y = sim.windowHeight - SHEEP_BODY_HEIGHT - SHEEP_LEG_LENGTH;
+    sheep.vx = SHEEP_WALK_SPEED_MIN;
+    sheep.state = SHEEP_STATE_WALKING;
+    sheep.stateTimer = 10.0;
+    sim.entities.push_back(sheep);
+
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = bird.x;
+    ev.y = bird.y;
+    sim_apply_click(sim, ev);
+
+    REQUIRE(sim.entities[0].kind == EntityKind::Bird);
+    REQUIRE(sim.entities[0].baseSpeed == Approx(BIRD_SPEED_MIN));
+    REQUIRE(sim.entities[1].state == SHEEP_STATE_WALKING);
+    for (const Blade& b : sim.blades) REQUIRE(b.cutAnimStart < 0.0);
+}
+
+TEST_CASE("Bird flyby Poisson inter-arrivals keep expected mean", "[bird][poisson]") {
+    const uint64_t seed = 0x510B17D00ull;
+    Sim sim = build_sim(seed);
+    reset_bird_schedule(sim, seed);
+
+    double prev = sim.globalTime;
+    double totalInterval = 0.0;
+    constexpr int Events = 100;
+    for (int i = 0; i < Events; ++i) {
+        sim.globalTime = sim.nextBirdFlybyAtTime;
+        totalInterval += sim.globalTime - prev;
+        prev = sim.globalTime;
+        sim_tick_bird_flybys(sim);
+        sim.entities.clear();
+    }
+
+    const double expectedMean = 3600.0 / BIRD_FLYBY_SPAWN_RATE_PER_HOUR;
+    REQUIRE((totalInterval / Events) == Approx(expectedMean).epsilon(0.20));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/blade_gen_tests.cpp

@@ -0,0 +1,153 @@
+// blade_gen_tests.cpp
+//
+// Snapshot + invariant tests for procedural blade generation (architecture.md §5).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+#include "snapshot_data.h"
+
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+using namespace desktopgrass::test;
+
+namespace {
+
+void requireBladeEquals(const Blade& actual, const SnapshotBlade& expected, std::size_t index) {
+    INFO("blade index = " << index);
+    REQUIRE(actual.baseX           == Approx(expected.baseX          ).margin(1e-12));
+    REQUIRE(actual.height          == Approx(expected.height         ).margin(1e-12));
+    REQUIRE(actual.thickness       == Approx(expected.thickness      ).margin(1e-12));
+    REQUIRE(actual.hue             == expected.hue);
+    REQUIRE(actual.swayPhaseOffset == Approx(expected.sway          ).margin(1e-12));
+    REQUIRE(actual.stiffness       == Approx(expected.stiffness     ).margin(1e-12));
+    REQUIRE(actual.isFlower             == expected.isFlower);
+    REQUIRE(actual.flowerHeadColorIdx   == expected.flowerHeadColorIdx);
+    REQUIRE(actual.flowerHeadRadius     == Approx(expected.flowerHeadRadius).margin(1e-12));
+    REQUIRE(actual.heightBonus          == Approx(expected.heightBonus    ).margin(1e-12));
+}
+
+} // anonymous
+
+TEST_CASE("blade generation matches the canonical snapshot", "[blade-gen][snapshot]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+
+    REQUIRE(blades.size() == CANONICAL_BLADE_COUNT);
+
+    SECTION("first 10 blades match") {
+        for (std::size_t i = 0; i < 10; ++i) {
+            requireBladeEquals(blades[i], CANONICAL_FIRST_10[i], i);
+        }
+    }
+
+    SECTION("last 10 blades match") {
+        const std::size_t start = blades.size() - 10;
+        for (std::size_t i = 0; i < 10; ++i) {
+            requireBladeEquals(blades[start + i], CANONICAL_LAST_10[i], start + i);
+        }
+    }
+}
+
+TEST_CASE("blade fields stay within spec ranges", "[blade-gen]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+
+    constexpr double TWO_PI = 6.283185307179586;
+    for (std::size_t i = 0; i < blades.size(); ++i) {
+        const Blade& b = blades[i];
+        INFO("blade index = " << i);
+        REQUIRE(b.baseX           >= 0.0);
+        REQUIRE(b.baseX           <  1920.0);
+        REQUIRE(b.height          >= BLADE_HEIGHT_MIN);
+        REQUIRE(b.height          <  BLADE_HEIGHT_MAX);
+        REQUIRE(b.thickness       >= BLADE_THICKNESS_MIN);
+        REQUIRE(b.thickness       <  BLADE_THICKNESS_MAX);
+        REQUIRE(b.hue             <  PALETTE_SIZE);
+        REQUIRE(b.swayPhaseOffset >= 0.0);
+        REQUIRE(b.swayPhaseOffset <  TWO_PI);
+        REQUIRE(b.stiffness       >= STIFFNESS_MIN);
+        REQUIRE(b.stiffness       <  STIFFNESS_MAX);
+        REQUIRE(b.cutHeight        == Approx(1.0));
+        REQUIRE(b.gustVelocity     == Approx(0.0));
+        REQUIRE(b.cutAnimStart     == Approx(-1.0));
+        REQUIRE(b.cutInitialHeight == Approx(1.0));
+        if (b.isFlower) {
+            REQUIRE(b.flowerHeadColorIdx < FLOWER_PALETTE_SIZE);
+            REQUIRE(b.flowerHeadRadius >= FLOWER_HEAD_RADIUS_MIN);
+            REQUIRE(b.flowerHeadRadius <  FLOWER_HEAD_RADIUS_MAX);
+            REQUIRE(b.heightBonus      >= FLOWER_HEIGHT_BONUS_MIN);
+            REQUIRE(b.heightBonus      <  FLOWER_HEIGHT_BONUS_MAX);
+        } else {
+            REQUIRE(b.flowerHeadColorIdx == 0);
+            REQUIRE(b.flowerHeadRadius   == Approx(0.0));
+            REQUIRE(b.heightBonus        == Approx(1.0));
+        }
+    }
+}
+
+TEST_CASE("flower count is near configured probability and ordinary blades use defaults", "[blade-gen][flowers]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 100);
+
+    std::size_t flowerCount = 0;
+    for (const Blade& b : blades) {
+        if (b.isFlower) {
+            ++flowerCount;
+        } else {
+            REQUIRE(b.flowerHeadColorIdx == 0);
+            REQUIRE(b.flowerHeadRadius   == Approx(0.0));
+            REQUIRE(b.heightBonus        == Approx(1.0));
+        }
+    }
+
+    const double n  = static_cast<double>(blades.size());
+    const double p  = FLOWER_PROBABILITY;
+    const double mu = n * p;
+    const double sd = std::sqrt(n * p * (1.0 - p));
+    REQUIRE(flowerCount >= static_cast<std::size_t>(std::floor(mu - 3.0 * sd)));
+    REQUIRE(flowerCount <= static_cast<std::size_t>(std::ceil(mu + 3.0 * sd)));
+}
+
+TEST_CASE("blade baseX is strictly increasing", "[blade-gen]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 0);
+    for (std::size_t i = 1; i < blades.size(); ++i) {
+        INFO("between " << (i-1) << " and " << i);
+        REQUIRE(blades[i].baseX > blades[i-1].baseX);
+    }
+}
+
+TEST_CASE("blade generation is deterministic across repeat runs", "[blade-gen]") {
+    std::vector<Blade> a, b;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, a);
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, b);
+    REQUIRE(a.size() == b.size());
+    for (std::size_t i = 0; i < a.size(); ++i) {
+        REQUIRE(a[i].baseX           == b[i].baseX);
+        REQUIRE(a[i].height          == b[i].height);
+        REQUIRE(a[i].thickness       == b[i].thickness);
+        REQUIRE(a[i].hue             == b[i].hue);
+        REQUIRE(a[i].swayPhaseOffset == b[i].swayPhaseOffset);
+        REQUIRE(a[i].stiffness       == b[i].stiffness);
+    }
+}
+
+TEST_CASE("density scales blade count roughly linearly", "[blade-gen]") {
+    std::vector<Blade> low, high;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 0.5, low);
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 2.0, high);
+    REQUIRE(low.size()  > 0);
+    REQUIRE(high.size() > low.size() * 3);  // 4x density ≈ 4x blades, allow slack
+}
+
+TEST_CASE("blade count near plan default at density 1.25", "[blade-gen]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.25, blades);
+    // Plan target: ~400 blades per 1920 px at the v1 default density of 1.25.
+    REQUIRE(blades.size() >= 350);
+    REQUIRE(blades.size() <= 450);
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/bunny_tests.cpp

@@ -0,0 +1,311 @@
+// bunny_tests.cpp
+//
+// §18 Bunny critter tests. Mirrors Win2D BunnyTests.cs.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cwchar>
+
+using namespace desktopgrass;
+
+namespace {
+
+constexpr double Monitor1920 = 1920.0;
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+Sim build_grass_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    Sim sim = sim_init(seed, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Grass);
+    sim_set_critter(sim, CritterKind::Bunny);
+    return sim;
+}
+
+Entity bunny_entity(double x = 500.0, double vx = BUNNY_HOP_SPEED_MIN) {
+    Entity e{};
+    e.kind = EntityKind::Bunny;
+    e.size = BUNNY_BODY_RADIUS;
+    e.x = x;
+    e.y = STRIP_HEIGHT + HEADROOM - BUNNY_BODY_HEIGHT - BUNNY_LEG_LENGTH;
+    e.vx = vx;
+    e.rotationSpeed = std::abs(vx);
+    e.lifetime = -1.0;
+    e.state = BUNNY_STATE_HOPPING;
+    e.stateTimer = BUNNY_HOP_DURATION;
+    return e;
+}
+
+InputEvent click_event(double x, double y) {
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = x;
+    ev.y = y;
+    ev.time = 0.0;
+    return ev;
+}
+
+int prng_count(Prng& side, int minCount, int maxCount) {
+    const double draw = prng_uniform(side, static_cast<double>(minCount), static_cast<double>(maxCount + 1));
+    int count = static_cast<int>(std::floor(draw));
+    if (count < minCount) count = minCount;
+    if (count > maxCount) count = maxCount;
+    return count;
+}
+
+void advance_sheep(Prng& side, int count) {
+    for (int i = 0; i < count; ++i) {
+        const double margin = SHEEP_BODY_RADIUS + 8.0;
+        (void)prng_uniform(side, margin, Monitor1920 - margin);
+        (void)prng_uniform(side, SHEEP_WALK_SPEED_MIN, SHEEP_WALK_SPEED_MAX);
+        (void)prng_uniform(side, 0.0, 1.0);
+        (void)prng_next_u32(side);
+        (void)prng_uniform(side, SHEEP_WALK_DURATION_MIN, SHEEP_WALK_DURATION_MAX);
+        (void)prng_index(side, static_cast<uint32_t>(sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0])));
+    }
+}
+
+void advance_cats(Prng& side, int count) {
+    for (int i = 0; i < count; ++i) {
+        const double margin = CAT_BODY_RADIUS + 8.0;
+        (void)prng_uniform(side, margin, Monitor1920 - margin);
+        (void)prng_uniform(side, CAT_WALK_SPEED_MIN, CAT_WALK_SPEED_MAX);
+        (void)prng_uniform(side, 0.0, 1.0);
+        (void)prng_next_u32(side);
+        (void)prng_uniform(side, CAT_WALK_DURATION_MIN, CAT_WALK_DURATION_MAX);
+        (void)prng_index(side, static_cast<uint32_t>(sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0])));
+        (void)prng_index(side, static_cast<uint32_t>(CAT_COAT_VARIANT_COUNT));
+    }
+}
+
+bool bunny_name_in_pool(const Entity& e) {
+    if (e.nameIndex >= sizeof(BUNNY_NAME_POOL) / sizeof(BUNNY_NAME_POOL[0])) return false;
+    const wchar_t* name = BUNNY_NAME_POOL[e.nameIndex];
+    for (const wchar_t* candidate : BUNNY_NAME_POOL) {
+        if (std::wcscmp(name, candidate) == 0) return true;
+    }
+    return false;
+}
+
+} // namespace
+
+TEST_CASE("Bunny constants are pinned to spec values", "[bunny][constants]") {
+    REQUIRE(BUNNY_COUNT_MIN == 1);
+    REQUIRE(BUNNY_COUNT_MAX == 2);
+    REQUIRE(BUNNY_HOP_SPEED_MIN == Approx(22.0));
+    REQUIRE(BUNNY_HOP_SPEED_MAX == Approx(38.0));
+    REQUIRE(BUNNY_BODY_RADIUS == Approx(8.0));
+    REQUIRE(BUNNY_BODY_HEIGHT == Approx(6.5));
+    REQUIRE(BUNNY_HEAD_RADIUS == Approx(4.2));
+    REQUIRE(BUNNY_EAR_HEIGHT == Approx(9.0));
+    REQUIRE(BUNNY_EAR_WIDTH == Approx(2.2));
+    REQUIRE(BUNNY_EAR_SPACING == Approx(3.0));
+    REQUIRE(BUNNY_LEG_LENGTH == Approx(4.0));
+    REQUIRE(BUNNY_TAIL_RADIUS == Approx(2.4));
+    REQUIRE(BUNNY_BODY_COLOR == 0xFF8A6A4Au);
+    REQUIRE(BUNNY_BELLY_COLOR == 0xFFC4A98Du);
+    REQUIRE(BUNNY_EAR_COLOR == 0xFF8A6A4Au);
+    REQUIRE(BUNNY_EAR_INNER_COLOR == 0xFFD9A0A0u);
+    REQUIRE(BUNNY_TAIL_COLOR == 0xFFF7F4EBu);
+    REQUIRE(BUNNY_EYE_COLOR == 0xFF1A1208u);
+    REQUIRE(BUNNY_NOSE_COLOR == 0xFF8A4040u);
+    REQUIRE(BUNNY_STATE_HOPPING == 0);
+    REQUIRE(BUNNY_STATE_GRAZING == 1);
+    REQUIRE(BUNNY_STATE_IDLE == 2);
+    REQUIRE(BUNNY_STATE_SLEEPING == 3);
+    REQUIRE(BUNNY_STATE_STARTLED == 4);
+    REQUIRE(BUNNY_HOP_DURATION == Approx(0.40));
+    REQUIRE(BUNNY_HOP_HEIGHT == Approx(8.0));
+    REQUIRE(BUNNY_HOP_GAP_MIN == Approx(0.05));
+    REQUIRE(BUNNY_HOP_GAP_MAX == Approx(0.20));
+    REQUIRE(BUNNY_GRAZE_DURATION_MIN == Approx(2.5));
+    REQUIRE(BUNNY_GRAZE_DURATION_MAX == Approx(4.5));
+    REQUIRE(BUNNY_IDLE_DURATION_MIN == Approx(2.0));
+    REQUIRE(BUNNY_IDLE_DURATION_MAX == Approx(4.0));
+    REQUIRE(BUNNY_SLEEP_DURATION_MIN == Approx(6.0));
+    REQUIRE(BUNNY_SLEEP_DURATION_MAX == Approx(12.0));
+    REQUIRE(BUNNY_GRAZE_PROBABILITY == Approx(0.55));
+    REQUIRE(BUNNY_IDLE_PROBABILITY == Approx(0.30));
+    REQUIRE(BUNNY_SLEEP_PROB == Approx(0.05));
+    REQUIRE(BUNNY_STARTLE_RADIUS == Approx(90.0));
+    REQUIRE(BUNNY_STARTLE_BOOST == Approx(2.0));
+    REQUIRE(BUNNY_STARTLE_HOP_HEIGHT == Approx(14.0));
+    REQUIRE(BUNNY_STARTLE_DURATION == Approx(3.0));
+    REQUIRE(BUNNY_NOSE_TWITCH_FREQ == Approx(6.0));
+    REQUIRE(BUNNY_NOSE_TWITCH_AMP == Approx(0.5));
+    REQUIRE(BUNNY_EAR_WIGGLE_FREQ == Approx(1.2));
+    REQUIRE(BUNNY_EAR_WIGGLE_AMP == Approx(0.20));
+    REQUIRE(BUNNY_ZZZ_CYCLE_SEC == Approx(SHEEP_ZZZ_CYCLE_SEC));
+    REQUIRE(BUNNY_ZZZ_RISE == Approx(SHEEP_ZZZ_RISE * 0.7));
+    REQUIRE(BUNNY_ZZZ_SIZE_START == Approx(SHEEP_ZZZ_SIZE_START * 0.7));
+    REQUIRE(BUNNY_ZZZ_SIZE_END == Approx(SHEEP_ZZZ_SIZE_END * 0.7));
+    REQUIRE(sizeof(BUNNY_NAME_POOL) / sizeof(BUNNY_NAME_POOL[0]) == 12);
+    REQUIRE(std::wcscmp(BUNNY_NAME_POOL[0], L"Clover") == 0);
+    REQUIRE(std::wcscmp(BUNNY_NAME_POOL[11], L"Snowdrop") == 0);
+}
+
+TEST_CASE("Grass generation produces bunny count in range", "[bunny][gen]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = build_grass_sim(seed);
+        const int bunnies = count_kind(sim, EntityKind::Bunny);
+        REQUIRE(bunnies >= BUNNY_COUNT_MIN);
+        REQUIRE(bunnies <= BUNNY_COUNT_MAX);
+    }
+}
+
+TEST_CASE("Bunnies are Grass scene only", "[bunny][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+    sim_set_critter(sim, CritterKind::Bunny);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+}
+
+TEST_CASE("Generated bunnies have speed range", "[bunny][gen]") {
+    Sim sim = build_grass_sim();
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Bunny) continue;
+        REQUIRE(std::abs(e.vx) >= BUNNY_HOP_SPEED_MIN);
+        REQUIRE(std::abs(e.vx) < BUNNY_HOP_SPEED_MAX);
+        REQUIRE(e.rotationSpeed == Approx(std::abs(e.vx)));
+    }
+}
+
+TEST_CASE("Generated bunnies have names in pool", "[bunny][gen]") {
+    Sim sim = build_grass_sim();
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Bunny) continue;
+        REQUIRE(bunny_name_in_pool(e));
+    }
+}
+
+TEST_CASE("Bunny PRNG draw order follows sheep and cats", "[bunny][prng]") {
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+
+    Sim sim = build_grass_sim();
+
+    const int sheepCount = prng_count(side, SHEEP_COUNT_MIN, SHEEP_COUNT_MAX);
+    advance_sheep(side, sheepCount);
+    const int catCount = prng_count(side, CAT_COUNT_MIN, CAT_COUNT_MAX);
+    advance_cats(side, catCount);
+    const int bunnyCount = prng_count(side, BUNNY_COUNT_MIN, BUNNY_COUNT_MAX);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == bunnyCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Bunny) continue;
+        const double margin = BUNNY_BODY_RADIUS + 8.0;
+        const double xFrac = prng_uniform(side, 0.0, 1.0);
+        const double expectedX = margin + xFrac * (Monitor1920 - 2.0 * margin);
+        const uint64_t vxSign = prng_next_u64(side) & 1ull;
+        const double expectedDir = vxSign != 0ull ? 1.0 : -1.0;
+        const double expectedSpeed = prng_uniform(side, BUNNY_HOP_SPEED_MIN, BUNNY_HOP_SPEED_MAX);
+        const uint8_t expectedName = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(sizeof(BUNNY_NAME_POOL) / sizeof(BUNNY_NAME_POOL[0]))));
+        REQUIRE(e.x == Approx(expectedX));
+        REQUIRE(e.vx == Approx(expectedDir * expectedSpeed));
+        REQUIRE(e.nameIndex == expectedName);
+        ++seen;
+    }
+    REQUIRE(seen == bunnyCount);
+}
+
+TEST_CASE("Bunny edge bounce flips direction", "[bunny][motion]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim.currentScene = Scene::Desert;
+    sim.entities.clear();
+    Entity e = bunny_entity(Monitor1920 - (BUNNY_BODY_RADIUS + 2.0) + 0.1, BUNNY_HOP_SPEED_MIN);
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(sim.entities.front().vx < 0.0);
+}
+
+TEST_CASE("Bunny startle radius hops away and outside click does nothing", "[bunny][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim.entities.clear();
+    Entity e = bunny_entity(500.0, -BUNNY_HOP_SPEED_MIN);
+    e.state = BUNNY_STATE_IDLE;
+    e.stateTimer = 3.0;
+    sim.entities.push_back(e);
+
+    sim_apply_click(sim, click_event(500.0 - 20.0, e.y));
+    REQUIRE(sim.entities.front().state == BUNNY_STATE_STARTLED);
+    REQUIRE(sim.entities.front().vx > 0.0);
+    REQUIRE(sim.entities.front().stateTimer == Approx(BUNNY_STARTLE_DURATION));
+
+    Entity after = sim.entities.front();
+    const double vxBefore = after.vx;
+    const uint8_t stateBefore = after.state;
+    sim_apply_click(sim, click_event(after.x + BUNNY_STARTLE_RADIUS + 10.0, after.y));
+    REQUIRE(sim.entities.front().state == stateBefore);
+    REQUIRE(sim.entities.front().vx == Approx(vxBefore));
+}
+
+TEST_CASE("Bunny wakes from sleep on startle", "[bunny][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim.entities.clear();
+    Entity e = bunny_entity(500.0, BUNNY_HOP_SPEED_MIN);
+    e.state = BUNNY_STATE_SLEEPING;
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+
+    sim_apply_click(sim, click_event(e.x + 10.0, e.y));
+
+    REQUIRE(sim.entities.front().state == BUNNY_STATE_STARTLED);
+    REQUIRE(sim.entities.front().state != BUNNY_STATE_SLEEPING);
+    REQUIRE(sim.entities.front().vx < 0.0);
+}
+
+TEST_CASE("Bunny hop arc is bounded", "[bunny][motion]") {
+    REQUIRE(bunny_hop_y_offset(0.0, false) == Approx(0.0));
+    REQUIRE(bunny_hop_y_offset(BUNNY_HOP_DURATION, false) == Approx(0.0).margin(1e-12));
+    const double peak = bunny_hop_y_offset(BUNNY_HOP_DURATION * 0.5, false);
+    REQUIRE(peak > 0.0);
+    REQUIRE(peak <= BUNNY_HOP_HEIGHT);
+}
+
+TEST_CASE("Bunny state transition probabilities are stable", "[bunny][state]") {
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+    constexpr int N = 10000;
+    int graze = 0;
+    int idle = 0;
+    int sleep = 0;
+    for (int i = 0; i < N; ++i) {
+        const uint8_t state = bunny_choose_rest_state(p);
+        if (state == BUNNY_STATE_GRAZING) ++graze;
+        else if (state == BUNNY_STATE_IDLE) ++idle;
+        else if (state == BUNNY_STATE_SLEEPING) ++sleep;
+    }
+
+    const double sleepProb = BUNNY_SLEEP_PROB;
+    const double activeWeight = BUNNY_GRAZE_PROBABILITY + BUNNY_IDLE_PROBABILITY;
+    const double expectedGraze = (1.0 - sleepProb) * BUNNY_GRAZE_PROBABILITY / activeWeight;
+    const double expectedIdle = (1.0 - sleepProb) * BUNNY_IDLE_PROBABILITY / activeWeight;
+    REQUIRE(static_cast<double>(sleep) / N == Approx(sleepProb).margin(0.02));
+    REQUIRE(static_cast<double>(graze) / N == Approx(expectedGraze).margin(0.02));
+    REQUIRE(static_cast<double>(idle) / N == Approx(expectedIdle).margin(0.02));
+}
+
+TEST_CASE("Bunny sleep probability is stable", "[bunny][state]") {
+    constexpr int N = 20000;
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ 0x1234ull);
+    int sleep = 0;
+    for (int i = 0; i < N; ++i) {
+        if (bunny_choose_rest_state(p) == BUNNY_STATE_SLEEPING) ++sleep;
+    }
+    REQUIRE(static_cast<double>(sleep) / N == Approx(BUNNY_SLEEP_PROB).margin(0.02));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/butterfly_tests.cpp

@@ -0,0 +1,180 @@
+// butterfly_tests.cpp - §17.6 ambient Butterfly tests.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+
+using namespace desktopgrass;
+
+namespace {
+constexpr double Monitor1920 = 1920.0;
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+Sim build_grass_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    Sim sim = sim_init(seed, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Grass);
+    return sim;
+}
+
+int prng_count(Prng& side, int minCount, int maxCount) {
+    const double draw = prng_uniform(side, static_cast<double>(minCount), static_cast<double>(maxCount + 1));
+    int count = static_cast<int>(std::floor(draw));
+    if (count < minCount) count = minCount;
+    if (count > maxCount) count = maxCount;
+    return count;
+}
+
+const Entity* first_butterfly(const Sim& sim) {
+    for (const Entity& e : sim.entities) if (e.kind == EntityKind::Butterfly) return &e;
+    return nullptr;
+}
+} // namespace
+
+TEST_CASE("Butterfly constants are pinned to spec values", "[butterfly][constants]") {
+    REQUIRE(BUTTERFLY_COUNT_MIN == 2);
+    REQUIRE(BUTTERFLY_COUNT_MAX == 4);
+    REQUIRE(BUTTERFLY_SPEED_MIN == Approx(18.0));
+    REQUIRE(BUTTERFLY_SPEED_MAX == Approx(32.0));
+    REQUIRE(BUTTERFLY_BODY_LENGTH == Approx(2.4));
+    REQUIRE(BUTTERFLY_WING_RADIUS == Approx(3.5));
+    REQUIRE(BUTTERFLY_WING_OFFSET == Approx(2.2));
+    REQUIRE(BUTTERFLY_FLUTTER_FREQ == Approx(16.0));
+    REQUIRE(BUTTERFLY_FLUTTER_MIN_SCALE == Approx(0.20));
+    REQUIRE(BUTTERFLY_MEANDER_FREQ_Y == Approx(0.8));
+    REQUIRE(BUTTERFLY_MEANDER_AMP_Y == Approx(16.0));
+    REQUIRE(BUTTERFLY_MEANDER_FREQ_X == Approx(0.5));
+    REQUIRE(BUTTERFLY_MEANDER_AMP_X == Approx(0.4));
+    REQUIRE(BUTTERFLY_ALTITUDE_MIN == Approx(18.0));
+    REQUIRE(BUTTERFLY_ALTITUDE_MAX == Approx(70.0));
+    REQUIRE(BUTTERFLY_BODY_COLOR == 0xFF2A2018u);
+    REQUIRE(BUTTERFLY_COLOR_COUNT == 5);
+    REQUIRE(BUTTERFLY_PRNG_SALT == 0xB07DEF1E0001ull);
+}
+
+TEST_CASE("Grass generation produces butterfly count in range", "[butterfly][gen]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = build_grass_sim(seed);
+        REQUIRE(count_kind(sim, EntityKind::Butterfly) >= BUTTERFLY_COUNT_MIN);
+        REQUIRE(count_kind(sim, EntityKind::Butterfly) <= BUTTERFLY_COUNT_MAX);
+    }
+}
+
+TEST_CASE("Butterflies are Grass scene only", "[butterfly][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(count_kind(sim, EntityKind::Butterfly) == 0);
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(count_kind(sim, EntityKind::Butterfly) == 0);
+}
+
+TEST_CASE("Generated butterflies have speed altitude and color ranges", "[butterfly][gen]") {
+    Sim sim = build_grass_sim();
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Butterfly) continue;
+        REQUIRE(e.baseSpeed >= BUTTERFLY_SPEED_MIN);
+        REQUIRE(e.baseSpeed <  BUTTERFLY_SPEED_MAX);
+        REQUIRE(e.altitudeAnchor >= BUTTERFLY_ALTITUDE_MIN);
+        REQUIRE(e.altitudeAnchor <  BUTTERFLY_ALTITUDE_MAX);
+        REQUIRE(e.colorVariant < BUTTERFLY_COLOR_COUNT);
+    }
+}
+
+TEST_CASE("Butterfly PRNG draw order matches side stream", "[butterfly][prng]") {
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ BUTTERFLY_PRNG_SALT);
+    Sim sim = build_grass_sim();
+
+    const int expectedCount = prng_count(side, BUTTERFLY_COUNT_MIN, BUTTERFLY_COUNT_MAX);
+    REQUIRE(count_kind(sim, EntityKind::Butterfly) == expectedCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Butterfly) continue;
+        const double xFrac = prng_uniform(side, 0.0, 1.0);
+        const double yFrac = prng_uniform(side, 0.0, 1.0);
+        const uint64_t vxSign = prng_next_u64(side) & 1ull;
+        const double expectedDir = vxSign != 0ull ? 1.0 : -1.0;
+        const double expectedSpeed = prng_uniform(side, BUTTERFLY_SPEED_MIN, BUTTERFLY_SPEED_MAX);
+        const uint8_t expectedColor = static_cast<uint8_t>(prng_index(side, static_cast<uint32_t>(BUTTERFLY_COLOR_COUNT)));
+        const double expectedPhaseY = prng_uniform(side, 0.0, 2.0 * 3.14159265358979323846);
+        const double expectedPhaseX = prng_uniform(side, 0.0, 2.0 * 3.14159265358979323846);
+        const double expectedAltitude = BUTTERFLY_ALTITUDE_MIN + yFrac * (BUTTERFLY_ALTITUDE_MAX - BUTTERFLY_ALTITUDE_MIN);
+        const double expectedVx = expectedDir * expectedSpeed * (1.0 + BUTTERFLY_MEANDER_AMP_X * std::sin(expectedPhaseX));
+
+        REQUIRE(e.x == Approx(xFrac * Monitor1920));
+        REQUIRE(e.altitudeAnchor == Approx(expectedAltitude));
+        REQUIRE(e.baseSpeed == Approx(expectedSpeed));
+        REQUIRE(e.vx == Approx(expectedVx));
+        REQUIRE(e.colorVariant == expectedColor);
+        REQUIRE(e.phaseY == Approx(expectedPhaseY));
+        REQUIRE(e.phaseX == Approx(expectedPhaseX));
+        ++seen;
+    }
+    REQUIRE(seen == expectedCount);
+}
+
+TEST_CASE("Butterfly edge wrap preserves altitude anchor", "[butterfly][motion]") {
+    Sim sim = build_grass_sim();
+    auto it = std::find_if(sim.entities.begin(), sim.entities.end(), [](const Entity& e) { return e.kind == EntityKind::Butterfly; });
+    REQUIRE(it != sim.entities.end());
+    const double margin = BUTTERFLY_WING_OFFSET + BUTTERFLY_WING_RADIUS;
+    it->x = Monitor1920 + margin + 1.0;
+    it->vx = std::abs(it->vx);
+    const double altitude = it->altitudeAnchor;
+    sim.currentScene = Scene::Desert;
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(it->x == Approx(-margin));
+    REQUIRE(it->altitudeAnchor == Approx(altitude));
+}
+
+TEST_CASE("Butterflies do not interact with cuts or pets", "[butterfly][interaction]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim.entities.clear();
+    Entity butterfly{};
+    butterfly.kind = EntityKind::Butterfly;
+    butterfly.x = 500.0;
+    butterfly.y = sim.windowHeight - STRIP_HEIGHT - 5.0;
+    butterfly.vx = BUTTERFLY_SPEED_MIN;
+    butterfly.baseSpeed = BUTTERFLY_SPEED_MIN;
+    butterfly.altitudeAnchor = BUTTERFLY_ALTITUDE_MIN;
+    butterfly.lifetime = -1.0;
+    sim.entities.push_back(butterfly);
+    Entity sheep{};
+    sheep.kind = EntityKind::Sheep;
+    sheep.x = butterfly.x;
+    sheep.y = sim.windowHeight - SHEEP_BODY_HEIGHT - SHEEP_LEG_LENGTH;
+    sheep.vx = SHEEP_WALK_SPEED_MIN;
+    sheep.state = SHEEP_STATE_WALKING;
+    sheep.stateTimer = 10.0;
+    sim.entities.push_back(sheep);
+
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = butterfly.x;
+    ev.y = butterfly.y;
+    sim_apply_click(sim, ev);
+
+    REQUIRE(sim.entities[0].kind == EntityKind::Butterfly);
+    REQUIRE(sim.entities[0].baseSpeed == Approx(BUTTERFLY_SPEED_MIN));
+    REQUIRE(sim.entities[1].state == SHEEP_STATE_WALKING);
+    for (const Blade& b : sim.blades) REQUIRE(b.cutAnimStart < 0.0);
+}
+
+TEST_CASE("Butterfly wing scale stays within flutter bounds", "[butterfly][render]") {
+    for (int i = 0; i < 200; ++i) {
+        const double t = i * 0.05;
+        const double scale = butterfly_wing_scale(t, 1.3);
+        REQUIRE(scale >= BUTTERFLY_FLUTTER_MIN_SCALE);
+        REQUIRE(scale <= 1.0);
+    }
+}
+

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/cat_coat_tests.cpp

@@ -0,0 +1,158 @@
+// cat_coat_tests.cpp
+//
+// §17 Cat coat palette and deterministic coat variant tests. Mirrors Win2D CatCoatTests.cs.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <cmath>
+#include <cstdint>
+
+using namespace desktopgrass;
+
+namespace {
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    int n = 0;
+    for (const Entity& e : sim.entities) if (e.kind == kind) ++n;
+    return n;
+}
+
+constexpr CatCoatPalette EXPECTED_CAT_COATS[CAT_COAT_VARIANT_COUNT] = {
+    { 0xFF6B6259u, 0xFF3D3733u, 0xFF6B6259u, 0xFF3D3733u, 0xFF1A1614u },
+    { 0xFFD89A6Fu, 0xFFA56B40u, 0xFFD89A6Fu, 0xFFA56B40u, 0xFF2B1A0Eu },
+    { 0xFF2A2522u, 0xFF140F0Cu, 0xFF2A2522u, 0xFF140F0Cu, 0xFFD9B85Bu },
+    { 0xFFEDE9E1u, 0xFFBDB7ABu, 0xFFEDE9E1u, 0xFFBDB7ABu, 0xFF1F1817u },
+    { 0xFF7A5F3Cu, 0xFF4E3F26u, 0xFF7A5F3Cu, 0xFF4E3F26u, 0xFF1A1108u },
+    { 0xFFC9B898u, 0xFF8E7F6Bu, 0xFFC9B898u, 0xFF8E7F6Bu, 0xFF2E251Du },
+};
+
+uint8_t next_cat_coat_after_prefix(Prng& side) {
+    (void)prng_uniform(side, CAT_BODY_RADIUS + 8.0, 1920.0 - (CAT_BODY_RADIUS + 8.0));
+    (void)prng_uniform(side, CAT_WALK_SPEED_MIN, CAT_WALK_SPEED_MAX);
+    (void)prng_uniform(side, 0.0, 1.0);
+    (void)prng_next_u32(side);
+    (void)prng_uniform(side, CAT_WALK_DURATION_MIN, CAT_WALK_DURATION_MAX);
+    (void)prng_index(side, static_cast<uint32_t>(sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0])));
+    return static_cast<uint8_t>(prng_index(side, static_cast<uint32_t>(CAT_COAT_VARIANT_COUNT)));
+}
+
+} // namespace
+
+TEST_CASE("Cat coat variant count is pinned", "[cat][coat][constants]") {
+    REQUIRE(CAT_COAT_VARIANT_COUNT == 6);
+}
+
+TEST_CASE("Cat coat palette zero matches backward-compatible aliases", "[cat][coat][constants]") {
+    REQUIRE(CAT_COAT_PALETTES[0].body == CAT_BODY_COLOR);
+    REQUIRE(CAT_COAT_PALETTES[0].leg  == CAT_LEG_COLOR);
+    REQUIRE(CAT_COAT_PALETTES[0].face == CAT_FACE_COLOR);
+    REQUIRE(CAT_COAT_PALETTES[0].ear  == CAT_EAR_COLOR);
+    REQUIRE(CAT_COAT_PALETTES[0].ink  == CAT_INK_COLOR);
+}
+
+TEST_CASE("All cat coat palettes are pinned", "[cat][coat][constants]") {
+    for (int i = 0; i < CAT_COAT_VARIANT_COUNT; ++i) {
+        CAPTURE(i);
+        REQUIRE(CAT_COAT_PALETTES[i].body == EXPECTED_CAT_COATS[i].body);
+        REQUIRE(CAT_COAT_PALETTES[i].leg  == EXPECTED_CAT_COATS[i].leg);
+        REQUIRE(CAT_COAT_PALETTES[i].face == EXPECTED_CAT_COATS[i].face);
+        REQUIRE(CAT_COAT_PALETTES[i].ear  == EXPECTED_CAT_COATS[i].ear);
+        REQUIRE(CAT_COAT_PALETTES[i].ink  == EXPECTED_CAT_COATS[i].ink);
+    }
+}
+
+TEST_CASE("Cat coat body colors are distinct", "[cat][coat][constants]") {
+    for (int i = 0; i < CAT_COAT_VARIANT_COUNT; ++i) {
+        for (int j = i + 1; j < CAT_COAT_VARIANT_COUNT; ++j) {
+            CAPTURE(i);
+            CAPTURE(j);
+            REQUIRE(CAT_COAT_PALETTES[i].body != CAT_COAT_PALETTES[j].body);
+        }
+    }
+}
+
+TEST_CASE("Canonical cat flock pins deterministic coat variants", "[cat][coat][gen]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+
+    const uint8_t expectedCoats[] = { 1 };
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        REQUIRE(seen < static_cast<int>(sizeof(expectedCoats) / sizeof(expectedCoats[0])));
+        REQUIRE(e.coatVariantIndex == expectedCoats[seen]);
+        ++seen;
+    }
+    REQUIRE(seen == static_cast<int>(sizeof(expectedCoats) / sizeof(expectedCoats[0])));
+}
+
+TEST_CASE("Cat coat PRNG draw follows nameIndex", "[cat][coat][prng]") {
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+
+    const double countDraw = prng_uniform(side, CAT_COUNT_MIN, CAT_COUNT_MAX + 1);
+    int expectedCount = static_cast<int>(std::floor(countDraw));
+    if (expectedCount < CAT_COUNT_MIN) expectedCount = CAT_COUNT_MIN;
+    if (expectedCount > CAT_COUNT_MAX) expectedCount = CAT_COUNT_MAX;
+    REQUIRE(count_kind(sim, EntityKind::Cat) == expectedCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        const uint8_t expectedCoat = next_cat_coat_after_prefix(side);
+        REQUIRE(e.coatVariantIndex == expectedCoat);
+        ++seen;
+    }
+    REQUIRE(seen == expectedCount);
+}
+
+TEST_CASE("Generated cat coats always stay within palette range", "[cat][coat][gen]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = sim_init(seed, 1920.0, DEFAULT_DENSITY);
+        sim_set_critter(sim, CritterKind::Cat);
+
+        int seen = 0;
+        for (const Entity& e : sim.entities) {
+            if (e.kind != EntityKind::Cat) continue;
+            REQUIRE(e.coatVariantIndex < CAT_COAT_VARIANT_COUNT);
+            ++seen;
+        }
+        REQUIRE(seen >= CAT_COUNT_MIN);
+        REQUIRE(seen <= CAT_COUNT_MAX);
+    }
+}
+
+TEST_CASE("Sheep keep default coat variant zero", "[cat][coat][sheep]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    REQUIRE(count_kind(sim, EntityKind::Sheep) >= SHEEP_COUNT_MIN);
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Sheep) continue;
+        REQUIRE(e.coatVariantIndex == 0);
+    }
+}
+
+TEST_CASE("Fixed cat count coat PRNG skips only the count draw", "[cat][coat][count][prng]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    sim_set_critter_count(sim, 3);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 3);
+
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        const uint8_t expectedCoat = next_cat_coat_after_prefix(side);
+        REQUIRE(e.coatVariantIndex == expectedCoat);
+        ++seen;
+    }
+    REQUIRE(seen == 3);
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/cat_tests.cpp

@@ -0,0 +1,332 @@
+// cat_tests.cpp
+//
+// §17 Cat critter tests. Mirrors Win2D CatTests.cs.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+
+using namespace desktopgrass;
+
+namespace {
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+Entity* first_kind(Sim& sim, EntityKind kind) {
+    for (Entity& e : sim.entities) if (e.kind == kind) return &e;
+    return nullptr;
+}
+
+const Entity* first_kind(const Sim& sim, EntityKind kind) {
+    for (const Entity& e : sim.entities) if (e.kind == kind) return &e;
+    return nullptr;
+}
+
+void keep_first_cat_only(Sim& sim) {
+    Entity* cat = first_kind(sim, EntityKind::Cat);
+    REQUIRE(cat != nullptr);
+    const Entity copy = *cat;
+    sim.entities.clear();
+    sim.entities.push_back(copy);
+}
+
+InputEvent click_event(double x, double y) {
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = x;
+    ev.y = y;
+    ev.time = 0.0;
+    return ev;
+}
+
+} // namespace
+
+TEST_CASE("CritterKind::Cat and CRITTER_COUNT are pinned", "[cat][enum]") {
+    REQUIRE(static_cast<int>(CritterKind::None)  == 0);
+    REQUIRE(static_cast<int>(CritterKind::Sheep) == 1);
+    REQUIRE(static_cast<int>(CritterKind::Cat)   == 2);
+    REQUIRE(static_cast<int>(CritterKind::Bunny) == 3);
+    REQUIRE(CRITTER_COUNT == 4);
+    REQUIRE(CRITTER_DEFAULT == CritterKind::None);
+}
+
+TEST_CASE("EntityKind::Cat is pinned", "[cat][enum]") {
+    REQUIRE(static_cast<int>(EntityKind::None)       == 0);
+    REQUIRE(static_cast<int>(EntityKind::Tumbleweed) == 1);
+    REQUIRE(static_cast<int>(EntityKind::Snowflake)  == 2);
+    REQUIRE(static_cast<int>(EntityKind::Sheep)      == 3);
+    REQUIRE(static_cast<int>(EntityKind::Cat)        == 4);
+}
+
+TEST_CASE("Cat constants are pinned to spec values", "[cat][constants]") {
+    REQUIRE(CAT_COUNT_MIN == 1);
+    REQUIRE(CAT_COUNT_MAX == 2);
+    REQUIRE(CAT_WALK_SPEED_MIN == Approx(10.0));
+    REQUIRE(CAT_WALK_SPEED_MAX == Approx(22.0));
+    REQUIRE(CAT_POUNCE_SPEED   == Approx(60.0));
+
+    REQUIRE(CAT_BODY_RADIUS    == Approx(11.0));
+    REQUIRE(CAT_BODY_HEIGHT    == Approx(7.0));
+    REQUIRE(CAT_HEAD_RADIUS    == Approx(4.5));
+    REQUIRE(CAT_LEG_LENGTH     == Approx(5.0));
+    REQUIRE(CAT_TAIL_LENGTH    == Approx(13.0));
+    REQUIRE(CAT_TAIL_THICKNESS == Approx(1.6));
+    REQUIRE(CAT_EAR_HEIGHT     == Approx(4.5));
+
+    REQUIRE(CAT_BODY_COLOR == 0xFF6B6259u);
+    REQUIRE(CAT_LEG_COLOR  == 0xFF3D3733u);
+    REQUIRE(CAT_FACE_COLOR == 0xFF6B6259u);
+    REQUIRE(CAT_EAR_COLOR  == 0xFF3D3733u);
+    REQUIRE(CAT_INK_COLOR  == 0xFF1A1614u);
+
+    REQUIRE(CAT_WALK_PERIOD    == Approx(0.50));
+    REQUIRE(CAT_LEG_CYCLE_AMP  == Approx(1.6));
+    REQUIRE(CAT_HEAD_BOB_AMP   == Approx(0.4));
+    REQUIRE(CAT_TAIL_SWAY_FREQ == Approx(1.2));
+    REQUIRE(CAT_TAIL_SWAY_AMP  == Approx(0.35));
+
+    REQUIRE(CAT_STATE_WALKING  == SHEEP_STATE_WALKING);
+    REQUIRE(CAT_STATE_IDLE     == SHEEP_STATE_IDLE);
+    REQUIRE(CAT_STATE_SLEEPING == SHEEP_STATE_SLEEPING);
+    REQUIRE(CAT_STATE_POUNCING == SHEEP_STATE_HOPPING);
+
+    REQUIRE(CAT_WALK_DURATION_MIN  == Approx(6.0));
+    REQUIRE(CAT_WALK_DURATION_MAX  == Approx(10.0));
+    REQUIRE(CAT_IDLE_DURATION_MIN  == Approx(4.0));
+    REQUIRE(CAT_IDLE_DURATION_MAX  == Approx(8.0));
+    REQUIRE(CAT_SLEEP_DURATION_MIN == Approx(20.0));
+    REQUIRE(CAT_SLEEP_DURATION_MAX == Approx(40.0));
+    REQUIRE(CAT_POUNCE_DURATION    == Approx(0.45));
+
+    REQUIRE(CAT_IDLE_PROBABILITY == Approx(0.65));
+    REQUIRE(CAT_SLEEP_PROBABILITY == Approx(0.30));
+    REQUIRE(CAT_SLEEP_FROM_IDLE_PROB == Approx(0.50));
+
+    REQUIRE(CAT_POUNCE_RADIUS == Approx(80.0));
+    REQUIRE(CAT_POUNCE_HEIGHT == Approx(9.0));
+    REQUIRE(CAT_CURIOUS_RADIUS == Approx(100.0));
+    REQUIRE(CAT_CURIOUS_HEAD_TURN_MAX == Approx(0.7));
+}
+
+TEST_CASE("sim_init defaults to None and does not generate cats until selected", "[cat][init]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    REQUIRE(sim.currentCritter == CritterKind::None);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+
+    sim_set_critter(sim, CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Cat) >= CAT_COUNT_MIN);
+}
+
+TEST_CASE("sim_set_critter(Cat) produces deterministic cats", "[cat][gen]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+
+    REQUIRE(sim.currentCritter == CritterKind::Cat);
+    const int k = count_kind(sim, EntityKind::Cat);
+    REQUIRE(k >= CAT_COUNT_MIN);
+    REQUIRE(k <= CAT_COUNT_MAX);
+
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        REQUIRE(e.state == CAT_STATE_WALKING);
+        REQUIRE(e.stateTimer >= CAT_WALK_DURATION_MIN);
+        REQUIRE(e.stateTimer <  CAT_WALK_DURATION_MAX);
+        REQUIRE(std::fabs(e.vx) >= CAT_WALK_SPEED_MIN);
+        REQUIRE(std::fabs(e.vx) <  CAT_WALK_SPEED_MAX);
+        const double margin = e.size + 8.0;
+        REQUIRE(e.x >= margin);
+        REQUIRE(e.x <= sim.monitorWidth - margin);
+        REQUIRE(e.y == Approx(sim.windowHeight - CAT_BODY_HEIGHT - CAT_LEG_LENGTH));
+        REQUIRE(e.size == Approx(CAT_BODY_RADIUS));
+        REQUIRE(e.lifetime < 0.0);
+        REQUIRE(e.nameIndex < sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0]));
+        REQUIRE(e.coatVariantIndex < CAT_COAT_VARIANT_COUNT);
+    }
+}
+
+TEST_CASE("Cat PRNG draw order matches a side stream", "[cat][prng]") {
+    // count, then per-cat: x, speed, dir-coin, seed, stateTimer, nameIndex, coatVariantIndex
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+
+    const double countDraw = prng_uniform(side, CAT_COUNT_MIN, CAT_COUNT_MAX + 1);
+    int expectedCount = static_cast<int>(std::floor(countDraw));
+    if (expectedCount < CAT_COUNT_MIN) expectedCount = CAT_COUNT_MIN;
+    if (expectedCount > CAT_COUNT_MAX) expectedCount = CAT_COUNT_MAX;
+    REQUIRE(count_kind(sim, EntityKind::Cat) == expectedCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        const double margin = CAT_BODY_RADIUS + 8.0;
+        const double expectedX = prng_uniform(side, margin, 1920.0 - margin);
+        const double expectedSpeed = prng_uniform(side, CAT_WALK_SPEED_MIN, CAT_WALK_SPEED_MAX);
+        const double dirCoin = prng_uniform(side, 0.0, 1.0);
+        const double expectedDir = (dirCoin < 0.5) ? -1.0 : 1.0;
+        const uint32_t expectedSeed = prng_next_u32(side);
+        const double expectedTimer = prng_uniform(side, CAT_WALK_DURATION_MIN, CAT_WALK_DURATION_MAX);
+        const uint8_t expectedNameIndex = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0]))));
+        const uint8_t expectedCoatVariantIndex = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(CAT_COAT_VARIANT_COUNT)));
+
+        REQUIRE(e.x == Approx(expectedX));
+        REQUIRE(e.vx == Approx(expectedSpeed * expectedDir));
+        REQUIRE(e.seed == expectedSeed);
+        REQUIRE(e.stateTimer == Approx(expectedTimer));
+        REQUIRE(e.nameIndex == expectedNameIndex);
+        REQUIRE(e.coatVariantIndex == expectedCoatVariantIndex);
+        ++seen;
+    }
+    REQUIRE(seen == expectedCount);
+}
+
+TEST_CASE("sim_set_critter(None) clears ambient cats", "[cat][toggle]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Cat) >= CAT_COUNT_MIN);
+
+    sim_set_critter(sim, CritterKind::None);
+    REQUIRE(sim.currentCritter == CritterKind::None);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+}
+
+TEST_CASE("Switching between critter species replaces the previous species", "[cat][toggle]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Cat) >= CAT_COUNT_MIN);
+    REQUIRE(count_kind(sim, EntityKind::Sheep) == 0);
+
+    sim_set_critter(sim, CritterKind::Sheep);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Sheep) >= SHEEP_COUNT_MIN);
+
+    sim_set_critter(sim, CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Sheep) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Cat) >= CAT_COUNT_MIN);
+}
+
+TEST_CASE("sim_set_scene gates active Cat to Grass", "[cat][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    const int catsGrass = count_kind(sim, EntityKind::Cat);
+    REQUIRE(catsGrass >= CAT_COUNT_MIN);
+
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(sim.currentCritter == CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(sim.currentCritter == CritterKind::Cat);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+
+    sim_set_scene(sim, Scene::Grass);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == catsGrass);
+}
+
+TEST_CASE("Click within CAT_POUNCE_RADIUS pounces toward the click", "[cat][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    keep_first_cat_only(sim);
+
+    Entity& cat = sim.entities.front();
+    cat.x = 500.0;
+    cat.vx = -CAT_WALK_SPEED_MIN;
+    cat.age = 5.0;
+
+    sim_apply_click(sim, click_event(cat.x + 16.0, sim.windowHeight - 20.0));
+
+    const Entity& after = sim.entities.front();
+    REQUIRE(after.state == CAT_STATE_POUNCING);
+    REQUIRE(after.stateTimer == Approx(CAT_POUNCE_DURATION));
+    REQUIRE(after.age == Approx(0.0));
+    REQUIRE(after.vx == Approx(CAT_POUNCE_SPEED));
+}
+
+TEST_CASE("Click outside CAT_POUNCE_RADIUS leaves cat alone", "[cat][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    keep_first_cat_only(sim);
+
+    Entity& cat = sim.entities.front();
+    cat.x = 500.0;
+    cat.vx = -CAT_WALK_SPEED_MIN;
+    const uint8_t stateBefore = cat.state;
+    const double vxBefore = cat.vx;
+
+    sim_apply_click(sim, click_event(cat.x + CAT_POUNCE_RADIUS + 5.0, sim.windowHeight - 20.0));
+
+    const Entity& after = sim.entities.front();
+    REQUIRE(after.state == stateBefore);
+    REQUIRE(after.vx == Approx(vxBefore));
+}
+
+TEST_CASE("Cats do not greet other cats", "[cat][greeting]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    keep_first_cat_only(sim);
+
+    Entity first = sim.entities.front();
+    first.x = 400.0;
+    first.vx = CAT_WALK_SPEED_MIN;
+    first.state = CAT_STATE_WALKING;
+    first.stateTimer = 10.0;
+    first.age = SHEEP_GREET_MIN_AGE + 1.0;
+    Entity second = first;
+    second.x = first.x + 20.0;
+    second.vx = -CAT_WALK_SPEED_MIN;
+    sim.entities.clear();
+    sim.entities.push_back(first);
+    sim.entities.push_back(second);
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 2);
+    for (const Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Cat) REQUIRE(e.state != SHEEP_STATE_GREETING);
+    }
+}
+
+TEST_CASE("Cats do not greet sheep", "[cat][greeting]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Cat);
+    keep_first_cat_only(sim);
+
+    Entity cat = sim.entities.front();
+    cat.x = 400.0;
+    cat.vx = CAT_WALK_SPEED_MIN;
+    cat.state = CAT_STATE_WALKING;
+    cat.stateTimer = 10.0;
+    cat.age = SHEEP_GREET_MIN_AGE + 1.0;
+
+    Entity sheep{};
+    sheep.kind = EntityKind::Sheep;
+    sheep.size = SHEEP_BODY_RADIUS;
+    sheep.x = cat.x + 20.0;
+    sheep.y = sim.windowHeight - SHEEP_BODY_HEIGHT - SHEEP_LEG_LENGTH;
+    sheep.vx = -SHEEP_WALK_SPEED_MIN;
+    sheep.age = SHEEP_GREET_MIN_AGE + 1.0;
+    sheep.lifetime = -1.0;
+    sheep.state = SHEEP_STATE_WALKING;
+    sheep.stateTimer = 10.0;
+
+    sim.entities.clear();
+    sim.entities.push_back(cat);
+    sim.entities.push_back(sheep);
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 1);
+    REQUIRE(count_kind(sim, EntityKind::Sheep) == 1);
+    for (const Entity& e : sim.entities) REQUIRE(e.state != SHEEP_STATE_GREETING);
+}
+

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/click_through_smoke_test.cpp

@@ -0,0 +1,176 @@
+#include "../third_party/catch2/catch.hpp"
+
+#define WIN32_LEAN_AND_MEAN
+#include <windows.h>
+
+#include <atomic>
+#include <chrono>
+#include <string>
+#include <thread>
+
+namespace {
+
+std::atomic<bool> g_probeReceivedLeftDown{false};
+
+enum class ClickThroughResult {
+    Passed,
+    Skipped,
+    Failed,
+};
+
+std::wstring unique_class_name(const wchar_t* suffix) {
+    return std::wstring(L"DesktopGrass.Native.ClickThrough.")
+        + std::to_wstring(GetCurrentProcessId()) + L"."
+        + std::to_wstring(GetTickCount64()) + L"."
+        + suffix;
+}
+
+LRESULT CALLBACK ProbeWndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
+    if (msg == WM_LBUTTONDOWN) {
+        g_probeReceivedLeftDown.store(true, std::memory_order_release);
+    }
+    return DefWindowProcW(hwnd, msg, wp, lp);
+}
+
+LRESULT CALLBACK OverlayWndProc(HWND hwnd, UINT msg, WPARAM wp, LPARAM lp) {
+    return DefWindowProcW(hwnd, msg, wp, lp);
+}
+
+void pump_messages_for(std::chrono::milliseconds duration) {
+    const auto deadline = std::chrono::steady_clock::now() + duration;
+    MSG msg{};
+    do {
+        while (PeekMessageW(&msg, nullptr, 0, 0, PM_REMOVE)) {
+            TranslateMessage(&msg);
+            DispatchMessageW(&msg);
+        }
+        if (g_probeReceivedLeftDown.load(std::memory_order_acquire)) {
+            return;
+        }
+        std::this_thread::sleep_for(std::chrono::milliseconds(5));
+    } while (std::chrono::steady_clock::now() < deadline);
+}
+
+bool has_interactive_desktop() {
+    if (GetConsoleWindow() == nullptr) {
+        return false;
+    }
+
+    HDESK inputDesktop = OpenInputDesktop(0, FALSE, DESKTOP_SWITCHDESKTOP);
+    if (inputDesktop == nullptr) {
+        return false;
+    }
+    CloseDesktop(inputDesktop);
+    return true;
+}
+
+ClickThroughResult spawn_probe_window_and_click_through_overlay() {
+    if (!has_interactive_desktop()) {
+        return ClickThroughResult::Skipped;
+    }
+
+    g_probeReceivedLeftDown.store(false, std::memory_order_release);
+
+    const HINSTANCE instance = GetModuleHandleW(nullptr);
+    const std::wstring probeClass = unique_class_name(L"Probe");
+    const std::wstring overlayClass = unique_class_name(L"Overlay");
+
+    WNDCLASSEXW probeWc{};
+    probeWc.cbSize = sizeof(probeWc);
+    probeWc.lpfnWndProc = ProbeWndProc;
+    probeWc.hInstance = instance;
+    probeWc.lpszClassName = probeClass.c_str();
+
+    WNDCLASSEXW overlayWc{};
+    overlayWc.cbSize = sizeof(overlayWc);
+    overlayWc.lpfnWndProc = OverlayWndProc;
+    overlayWc.hInstance = instance;
+    overlayWc.lpszClassName = overlayClass.c_str();
+
+    if (!RegisterClassExW(&probeWc)) {
+        return ClickThroughResult::Failed;
+    }
+    if (!RegisterClassExW(&overlayWc)) {
+        UnregisterClassW(probeClass.c_str(), instance);
+        return ClickThroughResult::Failed;
+    }
+
+    const int x = GetSystemMetrics(SM_XVIRTUALSCREEN) + 96;
+    const int y = GetSystemMetrics(SM_YVIRTUALSCREEN) + 96;
+    constexpr int kWidth = 96;
+    constexpr int kHeight = 64;
+    const int clickX = x + 24;
+    const int clickY = y + 24;
+
+    HWND probe = CreateWindowExW(
+        WS_EX_TOOLWINDOW | WS_EX_TOPMOST,
+        probeClass.c_str(), L"DesktopGrass click-through probe",
+        WS_POPUP | WS_VISIBLE,
+        x, y, kWidth, kHeight,
+        nullptr, nullptr, instance, nullptr);
+
+    HWND overlay = nullptr;
+    bool ok = probe != nullptr;
+    if (ok) {
+        SetWindowPos(probe, HWND_TOPMOST, x, y, kWidth, kHeight, SWP_SHOWWINDOW);
+
+        overlay = CreateWindowExW(
+            WS_EX_LAYERED | WS_EX_TRANSPARENT | WS_EX_TOPMOST |
+                WS_EX_TOOLWINDOW | WS_EX_NOACTIVATE,
+            overlayClass.c_str(), L"DesktopGrass click-through overlay",
+            WS_POPUP,
+            x, y, kWidth, kHeight,
+            nullptr, nullptr, instance, nullptr);
+        ok = overlay != nullptr;
+    }
+
+    if (ok) {
+        SetLayeredWindowAttributes(overlay, 0, 1, LWA_ALPHA);
+        ShowWindow(overlay, SW_SHOWNOACTIVATE);
+        SetWindowPos(overlay, HWND_TOPMOST, x, y, kWidth, kHeight,
+                     SWP_SHOWWINDOW | SWP_NOACTIVATE);
+        pump_messages_for(std::chrono::milliseconds(50));
+
+        if (!SetCursorPos(clickX, clickY)) {
+            ok = false;
+        }
+    }
+
+    ClickThroughResult result = ClickThroughResult::Failed;
+    if (ok) {
+        INPUT inputs[2]{};
+        inputs[0].type = INPUT_MOUSE;
+        inputs[0].mi.dwFlags = MOUSEEVENTF_LEFTDOWN;
+        inputs[1].type = INPUT_MOUSE;
+        inputs[1].mi.dwFlags = MOUSEEVENTF_LEFTUP;
+
+        const UINT sent = SendInput(2, inputs, sizeof(INPUT));
+        if (sent != 2) {
+            result = ClickThroughResult::Skipped;
+        } else {
+            pump_messages_for(std::chrono::milliseconds(200));
+            result = g_probeReceivedLeftDown.load(std::memory_order_acquire)
+                ? ClickThroughResult::Passed
+                : ClickThroughResult::Failed;
+        }
+    }
+
+    if (overlay) DestroyWindow(overlay);
+    if (probe) DestroyWindow(probe);
+    UnregisterClassW(overlayClass.c_str(), instance);
+    UnregisterClassW(probeClass.c_str(), instance);
+    return result;
+}
+
+} // namespace
+
+TEST_CASE("Overlay click-through allows input to reach windows beneath", "[smoke][input]") {
+    const ClickThroughResult result = spawn_probe_window_and_click_through_overlay();
+    if (result == ClickThroughResult::Skipped) {
+        WARN("Skipping click-through smoke test: requires an interactive desktop and SendInput.");
+        SUCCEED("Requires interactive session");
+        return;
+    }
+
+    REQUIRE(result == ClickThroughResult::Passed);
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/config_tests.cpp

@@ -0,0 +1,154 @@
+#include "../third_party/catch2/catch.hpp"
+#include "Config.h"
+
+#include <filesystem>
+#include <fstream>
+#include <sstream>
+#include <string>
+
+using namespace desktopgrass;
+
+namespace {
+
+std::filesystem::path test_config_path(const char* name) {
+    std::filesystem::path dir = std::filesystem::current_path()
+        / ".copilot-scratch"
+        / "native-config-tests"
+        / name;
+    std::error_code ec;
+    std::filesystem::remove_all(dir, ec);
+    std::filesystem::create_directories(dir);
+    return dir / "config.json";
+}
+
+void write_text(const std::filesystem::path& path, const std::string& text) {
+    std::filesystem::create_directories(path.parent_path());
+    std::ofstream file(path, std::ios::binary | std::ios::trunc);
+    file << text;
+}
+
+std::string read_text(const std::filesystem::path& path) {
+    std::ifstream file(path, std::ios::binary);
+    std::ostringstream buffer;
+    buffer << file.rdbuf();
+    return buffer.str();
+}
+
+} // namespace
+
+TEST_CASE("Config: missing file yields defaults and writes a template", "[config]") {
+    const std::filesystem::path path = test_config_path("missing");
+    REQUIRE_FALSE(std::filesystem::exists(path));
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+
+    CHECK(cfg.targetFps == config::kTargetFpsDefault);
+    CHECK(cfg.bladeDensity == Approx(config::kBladeDensityDefault));
+
+    // A default file should have been created and be re-readable (it is JSONC).
+    REQUIRE(std::filesystem::exists(path));
+    const config::Config reread = config::LoadConfig(path.wstring());
+    CHECK(reread.targetFps == config::kTargetFpsDefault);
+    CHECK(reread.bladeDensity == Approx(config::kBladeDensityDefault));
+}
+
+TEST_CASE("Config: valid values are parsed", "[config]") {
+    const std::filesystem::path path = test_config_path("valid");
+    write_text(path, "{ \"version\": 1, \"targetFps\": 60, \"bladeDensity\": 1.5 }");
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == 60);
+    CHECK(cfg.bladeDensity == Approx(1.5));
+}
+
+TEST_CASE("Config: out-of-range values are clamped", "[config]") {
+    const std::filesystem::path path = test_config_path("clamp");
+    write_text(path, "{ \"targetFps\": 1000, \"bladeDensity\": 99.0 }");
+
+    config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == config::kTargetFpsMax);
+    CHECK(cfg.bladeDensity == Approx(config::kBladeDensityMax));
+
+    write_text(path, "{ \"targetFps\": 0, \"bladeDensity\": 0.0 }");
+    cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == config::kTargetFpsMin);
+    CHECK(cfg.bladeDensity == Approx(config::kBladeDensityMin));
+}
+
+TEST_CASE("Config: JSONC comments and trailing commas are tolerated", "[config]") {
+    const std::filesystem::path path = test_config_path("jsonc");
+    write_text(path,
+        "{\n"
+        "  // a comment\n"
+        "  \"targetFps\": 24, /* inline */\n"
+        "  \"bladeDensity\": 2.0,\n"  // trailing comma below
+        "}\n");
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == 24);
+    CHECK(cfg.bladeDensity == Approx(2.0));
+}
+
+TEST_CASE("Config: malformed file falls back to defaults and is preserved", "[config]") {
+    const std::filesystem::path path = test_config_path("malformed");
+    write_text(path, "{ not valid json ");
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == config::kTargetFpsDefault);
+    CHECK(cfg.bladeDensity == Approx(config::kBladeDensityDefault));
+
+    // The user's (broken) file must be left untouched for them to fix.
+    CHECK(read_text(path) == "{ not valid json ");
+}
+
+TEST_CASE("Config: missing keys fall back to per-key defaults", "[config]") {
+    const std::filesystem::path path = test_config_path("partial");
+    write_text(path, "{ \"targetFps\": 45 }");
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == 45);
+    CHECK(cfg.bladeDensity == Approx(config::kBladeDensityDefault));
+    CHECK(cfg.swaySpeed == Approx(config::kSwaySpeedDefault));
+    CHECK(cfg.swayAmplitude == Approx(config::kSwayAmplitudeDefault));
+}
+
+TEST_CASE("Config: keys are matched case-insensitively", "[config]") {
+    const std::filesystem::path path = test_config_path("case-insensitive");
+    write_text(path,
+        "{ \"TargetFps\": 60, \"BLADEDENSITY\": 1.5, "
+        "\"SwaySpeed\": 0.5, \"swayamplitude\": 2.0 }");
+
+    const config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.targetFps == 60);
+    CHECK(cfg.bladeDensity == Approx(1.5));
+    CHECK(cfg.swaySpeed == Approx(0.5));
+    CHECK(cfg.swayAmplitude == Approx(2.0));
+}
+
+TEST_CASE("Config: sway knobs parse, clamp, and reject non-finite", "[config]") {
+    const std::filesystem::path path = test_config_path("sway");
+
+    // Defaults when absent.
+    write_text(path, "{ }");
+    config::Config cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.swaySpeed == Approx(config::kSwaySpeedDefault));
+    CHECK(cfg.swayAmplitude == Approx(config::kSwayAmplitudeDefault));
+
+    // Valid values parsed.
+    write_text(path, "{ \"swaySpeed\": 0.5, \"swayAmplitude\": 2.0 }");
+    cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.swaySpeed == Approx(0.5));
+    CHECK(cfg.swayAmplitude == Approx(2.0));
+
+    // Out-of-range clamped to bounds.
+    write_text(path, "{ \"swaySpeed\": 99.0, \"swayAmplitude\": -5.0 }");
+    cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.swaySpeed == Approx(config::kSwaySpeedMax));
+    CHECK(cfg.swayAmplitude == Approx(config::kSwayAmplitudeMin));
+
+    // Non-finite (inf from overflow) falls back to default, never poisons the sim.
+    write_text(path, "{ \"swaySpeed\": 1e999, \"swayAmplitude\": 1e999 }");
+    cfg = config::LoadConfig(path.wstring());
+    CHECK(cfg.swaySpeed == Approx(config::kSwaySpeedDefault));
+    CHECK(cfg.swayAmplitude == Approx(config::kSwayAmplitudeDefault));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/critter_tests.cpp

@@ -0,0 +1,379 @@
+// critter_tests.cpp
+//
+// Critter subsystem tests (architecture.md §13.3 / §16). Orthogonal to Scene.
+//
+// Coverage:
+//   * CritterKind discriminants are spec-locked ({None=0, Sheep=1}).
+//   * EntityKind::Sheep == 3 (added after the original {None, Tumbleweed,
+//     Snowflake} enum).
+//   * SHEEP_* and CRITTER_* constants are pinned to spec values.
+//   * sim_init defaults sim.currentCritter to None (no sheep until the user
+//     opts in via tray).
+//   * sim_set_critter(Sheep) on CANONICAL_TEST_SEED + 1920 produces
+//     deterministic count K ∈ [SHEEP_COUNT_MIN, SHEEP_COUNT_MAX], with
+//     every sheep entity well-formed: kind=Sheep, state=Walking, stateTimer
+//     in [WALK_DURATION_MIN, MAX], speed in [WALK_SPEED_MIN, MAX], x within
+//     monitor margins.
+//   * sim_set_critter(None) erases all sheep but preserves scene entities
+//     (snowflakes/tumbleweeds aren't touched).
+//   * sim_set_scene preserves the active critter — flipping Grass→Desert
+//     re-spawns sheep on the new scene.
+//   * Sheep PRNG draw order is bit-identical to a side-stream Prng for the
+//     locked sequence (count, then per-sheep: x, speed, dir-coin, seed,
+//     stateTimer, nameIndex).
+//   * Click within SHEEP_STARTLE_RADIUS pushes a sheep into Hopping, flips
+//     vx away from the cursor, and resets age.
+//   * Click outside SHEEP_STARTLE_RADIUS leaves sheep state untouched.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cwchar>
+
+using namespace desktopgrass;
+
+namespace {
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    int n = 0;
+    for (const Entity& e : sim.entities) if (e.kind == kind) ++n;
+    return n;
+}
+
+int count_sheep(const Sim& sim) {
+    return count_kind(sim, EntityKind::Sheep);
+}
+
+const Entity* first_sheep(const Sim& sim) {
+    for (const Entity& e : sim.entities) if (e.kind == EntityKind::Sheep) return &e;
+    return nullptr;
+}
+
+} // namespace
+
+TEST_CASE("CritterKind has spec-locked discriminants", "[critter][enum]") {
+    REQUIRE(static_cast<int>(CritterKind::None)  == 0);
+    REQUIRE(static_cast<int>(CritterKind::Sheep) == 1);
+    REQUIRE(static_cast<int>(CritterKind::Cat)   == 2);
+    REQUIRE(static_cast<int>(CritterKind::Bunny) == 3);
+    REQUIRE(static_cast<int>(EntityKind::Sheep)  == 3);
+    REQUIRE(static_cast<int>(EntityKind::Bunny)  == 6);
+    REQUIRE(static_cast<int>(EntityKind::Butterfly) == 7);
+    REQUIRE(static_cast<int>(EntityKind::Firefly) == 8);
+    REQUIRE(CRITTER_DEFAULT == CritterKind::None);
+}
+
+TEST_CASE("Sheep constants are pinned to spec values", "[critter][constants]") {
+    REQUIRE(SHEEP_COUNT_MIN      == 2);
+    REQUIRE(SHEEP_COUNT_MAX      == 3);
+    REQUIRE(sizeof(PET_COUNT_OPTIONS) / sizeof(PET_COUNT_OPTIONS[0]) == 6);
+    for (int i = 0; i < 6; ++i) REQUIRE(PET_COUNT_OPTIONS[i] == i + 1);
+    REQUIRE(PET_COUNT_DEFAULT_SHEEP == SHEEP_COUNT_MIN);
+    REQUIRE(PET_COUNT_DEFAULT_CAT == CAT_COUNT_MIN);
+    REQUIRE(PET_COUNT_MAX_PER_MONITOR == 6);
+    REQUIRE(sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0]) == 8);
+    REQUIRE(sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0]) == 8);
+    REQUIRE(std::wcscmp(SHEEP_NAME_POOL[0], L"Bessie") == 0);
+    REQUIRE(std::wcscmp(SHEEP_NAME_POOL[7], L"Hazel") == 0);
+    REQUIRE(std::wcscmp(CAT_NAME_POOL[0], L"Mittens") == 0);
+    REQUIRE(std::wcscmp(CAT_NAME_POOL[7], L"Juno") == 0);
+    REQUIRE(PET_NAME_HOVER_RADIUS == Approx(50.0));
+    REQUIRE(PET_NAME_FADE_DURATION == Approx(1.5));
+    REQUIRE(PET_NAME_FONT_SIZE == Approx(11.0));
+    REQUIRE(PET_NAME_OFFSET_Y == Approx(-8.0));
+    REQUIRE(PET_NAME_COLOR == 0xFFFFFFFFu);
+    REQUIRE(PET_NAME_SHADOW_COLOR == 0xC0000000u);
+    REQUIRE(SHEEP_WALK_SPEED_MIN == Approx(14.0));
+    REQUIRE(SHEEP_WALK_SPEED_MAX == Approx(26.0));
+    REQUIRE(SHEEP_BODY_RADIUS    == Approx(12.0));
+    REQUIRE(SHEEP_HEAD_RADIUS    == Approx(5.0));
+    REQUIRE(SHEEP_LEG_LENGTH     == Approx(5.5));
+
+    REQUIRE(SHEEP_STATE_WALKING  == 0);
+    REQUIRE(SHEEP_STATE_GRAZING  == 1);
+    REQUIRE(SHEEP_STATE_IDLE     == 2);
+    REQUIRE(SHEEP_STATE_SLEEPING == 3);
+    REQUIRE(SHEEP_STATE_HOPPING  == 4);
+
+    REQUIRE(SHEEP_HOP_DURATION   == Approx(0.55));
+    REQUIRE(SHEEP_HOP_HEIGHT     == Approx(11.0));
+    REQUIRE(SHEEP_STARTLE_RADIUS == Approx(64.0));
+    REQUIRE(SHEEP_STARTLE_BOOST  == Approx(1.6));
+
+    REQUIRE(SHEEP_GRAZE_PROBABILITY     == Approx(0.60));
+    REQUIRE(SHEEP_IDLE_PROBABILITY      == Approx(0.25));
+    REQUIRE(SHEEP_SLEEP_FROM_IDLE_PROB  == Approx(0.30));
+}
+
+TEST_CASE("sim_init defaults critter to None", "[critter][init]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    REQUIRE(sim.currentCritter == CritterKind::None);
+    REQUIRE(count_sheep(sim) == 0);
+}
+
+TEST_CASE("sim_set_critter(Sheep) produces deterministic flock", "[critter][gen]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    REQUIRE(sim.currentCritter == CritterKind::Sheep);
+    const int k = count_sheep(sim);
+    REQUIRE(k >= SHEEP_COUNT_MIN);
+    REQUIRE(k <= SHEEP_COUNT_MAX);
+
+    const double groundY = sim.windowHeight;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Sheep) continue;
+        REQUIRE(e.state == SHEEP_STATE_WALKING);
+        REQUIRE(e.stateTimer >= SHEEP_WALK_DURATION_MIN);
+        REQUIRE(e.stateTimer <  SHEEP_WALK_DURATION_MAX);
+        REQUIRE(std::fabs(e.vx) >= SHEEP_WALK_SPEED_MIN);
+        REQUIRE(std::fabs(e.vx) <  SHEEP_WALK_SPEED_MAX);
+        const double margin = e.size + 8.0;
+        REQUIRE(e.x >= margin);
+        REQUIRE(e.x <= sim.monitorWidth - margin);
+        REQUIRE(e.y == Approx(groundY - SHEEP_BODY_HEIGHT - SHEEP_LEG_LENGTH));
+        REQUIRE(e.lifetime < 0.0); // infinite — sheep don't expire
+        REQUIRE(e.nameIndex < sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0]));
+    }
+}
+
+TEST_CASE("Sheep PRNG draw order matches a side stream", "[critter][prng]") {
+    // Independent side stream that walks the documented sequence:
+    //   count
+    //   per-sheep: x, speed, dir-coin, seed, stateTimer, nameIndex
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    const double countDraw = prng_uniform(side, SHEEP_COUNT_MIN, SHEEP_COUNT_MAX + 1);
+    int expectedCount = static_cast<int>(std::floor(countDraw));
+    if (expectedCount < SHEEP_COUNT_MIN) expectedCount = SHEEP_COUNT_MIN;
+    if (expectedCount > SHEEP_COUNT_MAX) expectedCount = SHEEP_COUNT_MAX;
+    REQUIRE(count_sheep(sim) == expectedCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Sheep) continue;
+        const double margin = SHEEP_BODY_RADIUS + 8.0;
+        const double expectedX = prng_uniform(side, margin, 1920.0 - margin);
+        const double expectedSpeed = prng_uniform(side, SHEEP_WALK_SPEED_MIN, SHEEP_WALK_SPEED_MAX);
+        const double dirCoin = prng_uniform(side, 0.0, 1.0);
+        const double expectedDir = (dirCoin < 0.5) ? -1.0 : 1.0;
+        const uint32_t expectedSeed = prng_next_u32(side);
+        const double expectedTimer = prng_uniform(side, SHEEP_WALK_DURATION_MIN, SHEEP_WALK_DURATION_MAX);
+        const uint8_t expectedNameIndex = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0]))));
+
+        REQUIRE(e.x == Approx(expectedX));
+        REQUIRE(e.vx == Approx(expectedSpeed * expectedDir));
+        REQUIRE(e.seed == expectedSeed);
+        REQUIRE(e.stateTimer == Approx(expectedTimer));
+        REQUIRE(e.nameIndex == expectedNameIndex);
+        ++seen;
+    }
+    REQUIRE(seen == expectedCount);
+}
+
+TEST_CASE("canonical critter name indices are stable and species-local", "[critter][names]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+    const uint8_t expectedSheepNames[] = { 4, 7 };
+    int sheepSeen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Sheep) continue;
+        REQUIRE(sheepSeen < static_cast<int>(sizeof(expectedSheepNames) / sizeof(expectedSheepNames[0])));
+        REQUIRE(e.nameIndex == expectedSheepNames[sheepSeen]);
+        REQUIRE(std::wcscmp(SHEEP_NAME_POOL[e.nameIndex], sheepSeen == 0 ? L"Pippin" : L"Hazel") == 0);
+        ++sheepSeen;
+    }
+    REQUIRE(sheepSeen == 2);
+
+    sim_set_critter(sim, CritterKind::Cat);
+    const uint8_t expectedCatNames[] = { 4 };
+    int catSeen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Cat) continue;
+        REQUIRE(catSeen < static_cast<int>(sizeof(expectedCatNames) / sizeof(expectedCatNames[0])));
+        REQUIRE(e.nameIndex == expectedCatNames[catSeen]);
+        REQUIRE(e.nameIndex < sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0]));
+        REQUIRE(std::wcscmp(CAT_NAME_POOL[e.nameIndex], L"Smokey") == 0);
+        ++catSeen;
+    }
+    REQUIRE(catSeen == 1);
+}
+
+TEST_CASE("sim_set_critter_count(0) preserves random sheep count draw", "[critter][count]") {
+    bool sawMin = false;
+    bool sawMax = false;
+    for (uint64_t i = 0; i < 64; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = sim_init(seed, 1920.0, DEFAULT_DENSITY);
+        sim_set_critter_count(sim, 3);
+        sim_set_critter_count(sim, 0);
+        sim_set_critter(sim, CritterKind::Sheep);
+
+        Prng side;
+        prng_init(side, seed ^ CRITTER_PRNG_SALT);
+        const double countDraw = prng_uniform(side, SHEEP_COUNT_MIN, SHEEP_COUNT_MAX + 1);
+        int expectedCount = static_cast<int>(std::floor(countDraw));
+        if (expectedCount < SHEEP_COUNT_MIN) expectedCount = SHEEP_COUNT_MIN;
+        if (expectedCount > SHEEP_COUNT_MAX) expectedCount = SHEEP_COUNT_MAX;
+
+        REQUIRE(count_sheep(sim) == expectedCount);
+        sawMin = sawMin || expectedCount == SHEEP_COUNT_MIN;
+        sawMax = sawMax || expectedCount == SHEEP_COUNT_MAX;
+    }
+    REQUIRE(sawMin);
+    REQUIRE(sawMax);
+}
+
+TEST_CASE("fixed sheep count override skips the count PRNG draw", "[critter][count][prng]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+    sim_set_critter_count(sim, 3);
+
+    REQUIRE(sim.critterCountOverride == 3);
+    REQUIRE(count_sheep(sim) == 3);
+
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Sheep) continue;
+        const double margin = SHEEP_BODY_RADIUS + 8.0;
+        const double expectedX = prng_uniform(side, margin, 1920.0 - margin);
+        const double expectedSpeed = prng_uniform(side, SHEEP_WALK_SPEED_MIN, SHEEP_WALK_SPEED_MAX);
+        const double dirCoin = prng_uniform(side, 0.0, 1.0);
+        const double expectedDir = (dirCoin < 0.5) ? -1.0 : 1.0;
+        const uint32_t expectedSeed = prng_next_u32(side);
+        const double expectedTimer = prng_uniform(side, SHEEP_WALK_DURATION_MIN, SHEEP_WALK_DURATION_MAX);
+        const uint8_t expectedNameIndex = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0]))));
+
+        REQUIRE(e.x == Approx(expectedX));
+        REQUIRE(e.vx == Approx(expectedSpeed * expectedDir));
+        REQUIRE(e.seed == expectedSeed);
+        REQUIRE(e.stateTimer == Approx(expectedTimer));
+        REQUIRE(e.nameIndex == expectedNameIndex);
+        ++seen;
+    }
+    REQUIRE(seen == 3);
+}
+
+TEST_CASE("fixed critter count override supports tray range and clamps", "[critter][count]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    sim_set_critter_count(sim, 6);
+    REQUIRE(count_sheep(sim) == 6);
+
+    sim_set_critter_count(sim, 8);
+    REQUIRE(count_sheep(sim) == PET_COUNT_MAX_PER_MONITOR);
+
+    sim_set_critter(sim, CritterKind::Cat);
+    sim_set_critter_count(sim, 2);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 2);
+    REQUIRE(count_sheep(sim) == 0);
+}
+
+TEST_CASE("sim_set_critter(None) clears all ground critters",
+          "[critter][toggle]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+    REQUIRE(count_sheep(sim) >= SHEEP_COUNT_MIN);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+
+    sim_set_critter(sim, CritterKind::None);
+    REQUIRE(count_sheep(sim) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Cat) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Bunny) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Hedgehog) == 0);
+}
+
+TEST_CASE("sim_set_scene gates active sheep to Grass", "[critter][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+    const int sheepCountGrass = count_sheep(sim);
+    REQUIRE(sheepCountGrass >= SHEEP_COUNT_MIN);
+
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(count_sheep(sim) == 0);
+    REQUIRE(sim.currentCritter == CritterKind::Sheep);
+
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(count_sheep(sim) == 0);
+    REQUIRE(sim.currentCritter == CritterKind::Sheep);
+
+    sim_set_scene(sim, Scene::Grass);
+    REQUIRE(count_sheep(sim) == sheepCountGrass);
+}
+
+TEST_CASE("Click within SHEEP_STARTLE_RADIUS triggers hop away", "[critter][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    Entity* target = nullptr;
+    for (Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Sheep) { target = &e; break; }
+    }
+    REQUIRE(target != nullptr);
+
+    // Click 16 DIP to the left of the sheep — well within startle radius,
+    // inside the cut band (so the early y-gate doesn't reject).
+    const double clickX = target->x - 16.0;
+    const double clickY = sim.windowHeight - 20.0;
+    target->age = 5.0; // pre-set age to verify reset
+
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = clickX;
+    ev.y = clickY;
+    ev.time = 0.0;
+    sim_apply_click(sim, ev);
+
+    Entity* after = nullptr;
+    for (Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Sheep) { after = &e; break; }
+    }
+    REQUIRE(after != nullptr);
+    REQUIRE(after->state == SHEEP_STATE_HOPPING);
+    REQUIRE(after->stateTimer == Approx(SHEEP_HOP_DURATION));
+    REQUIRE(after->age == Approx(0.0));
+    REQUIRE(after->vx > 0.0); // sheep was right of click → vx flipped to +
+    REQUIRE(std::fabs(after->vx) <= SHEEP_WALK_SPEED_MAX * SHEEP_STARTLE_BOOST);
+}
+
+TEST_CASE("Click outside SHEEP_STARTLE_RADIUS leaves sheep alone", "[critter][click]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    sim_set_critter(sim, CritterKind::Sheep);
+
+    Entity* target = nullptr;
+    for (Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Sheep) { target = &e; break; }
+    }
+    REQUIRE(target != nullptr);
+    const uint8_t stateBefore = target->state;
+    const double  vxBefore    = target->vx;
+
+    // Click far away (300 DIP) but still in the cut band.
+    const double clickX = target->x + SHEEP_STARTLE_RADIUS + 200.0;
+    const double clickY = sim.windowHeight - 20.0;
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = clickX;
+    ev.y = clickY;
+    ev.time = 0.0;
+    sim_apply_click(sim, ev);
+
+    Entity* after = nullptr;
+    for (Entity& e : sim.entities) {
+        if (e.kind == EntityKind::Sheep) { after = &e; break; }
+    }
+    REQUIRE(after != nullptr);
+    REQUIRE(after->state == stateBefore);
+    REQUIRE(after->vx == Approx(vxBefore));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/cut_tests.cpp

@@ -0,0 +1,259 @@
+// cut_tests.cpp
+//
+// Cut state animation tests (architecture.md §9).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+#include "snapshot_data.h"
+
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+using namespace desktopgrass::test;
+
+namespace {
+
+Sim make_sim_with_blades(std::initializer_list<double> baseXs) {
+    Sim sim;
+    sim.windowHeight = STRIP_HEIGHT + HEADROOM;
+    for (double x : baseXs) {
+        Blade b{};
+        b.baseX            = x;
+        b.height           = 20.0;
+        b.thickness        = 1.5;
+        b.swayPhaseOffset  = 0.0;
+        b.stiffness        = 1.0;
+        b.cutHeight        = 1.0;
+        b.cutInitialHeight = 1.0;
+        b.cutAnimStart     = -1.0;
+        sim.blades.push_back(b);
+    }
+    return sim;
+}
+
+InputEvent click(double x, double y, double t) {
+    return InputEvent{ EventType::Click, x, y, t };
+}
+
+} // anonymous
+
+TEST_CASE("click inside cut band animates blades within radius to 0", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0, 110.0, 200.0});
+    const double y_in_band = sim.windowHeight - 40.0; // inside strip
+
+    InputEvent ev = click(100.0, y_in_band, 0.0);
+    sim_tick(sim, 0.0, &ev, 1);
+
+    // Apply 5 ticks of 50 ms (total = 250 ms > CUT_DURATION_SEC).
+    for (int i = 0; i < 5; ++i) {
+        sim_tick(sim, 0.05, nullptr, 0);
+    }
+
+    REQUIRE(sim.blades[0].cutHeight == Approx(0.0));
+    REQUIRE(sim.blades[0].cutAnimStart == Approx(-1.0));
+    REQUIRE(sim.blades[1].cutHeight == Approx(0.0));
+    // Blade at 200 is outside CUT_RADIUS = 30.
+    REQUIRE(sim.blades[2].cutHeight == Approx(1.0));
+    REQUIRE(sim.blades[2].cutAnimStart == Approx(-1.0));
+}
+
+TEST_CASE("cut animation is linear over CUT_DURATION_SEC", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y = sim.windowHeight - 40.0;
+
+    InputEvent ev = click(100.0, y, 0.0);
+    sim_tick(sim, 0.0, &ev, 1);
+    // After tick(0.0) globalTime = 0 still; cutAnimStart = 0.
+
+    // 50 ms in → cutHeight ≈ 0.75.
+    sim_tick(sim, 0.05, nullptr, 0);
+    REQUIRE(sim.blades[0].cutHeight == Approx(0.75).margin(1e-9));
+
+    // 100 ms in → 0.5.
+    sim_tick(sim, 0.05, nullptr, 0);
+    REQUIRE(sim.blades[0].cutHeight == Approx(0.5).margin(1e-9));
+
+    // 150 ms in → 0.25.
+    sim_tick(sim, 0.05, nullptr, 0);
+    REQUIRE(sim.blades[0].cutHeight == Approx(0.25).margin(1e-9));
+
+    // 200 ms in → 0.0 and idle.
+    sim_tick(sim, 0.05, nullptr, 0);
+    REQUIRE(sim.blades[0].cutHeight == Approx(0.0).margin(1e-9));
+    REQUIRE(sim.blades[0].cutAnimStart < 0.0);
+}
+
+TEST_CASE("click outside cut band is ignored", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y_above = sim.windowHeight - STRIP_HEIGHT - 5.0;
+
+    InputEvent ev = click(100.0, y_above, 0.0);
+    sim_tick(sim, 0.0, &ev, 1);
+
+    REQUIRE(sim.blades[0].cutHeight == Approx(1.0));
+    REQUIRE(sim.blades[0].cutAnimStart < 0.0);
+}
+
+TEST_CASE("repeat click on in-flight blade is idempotent", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y = sim.windowHeight - 40.0;
+
+    InputEvent first = click(100.0, y, 0.0);
+    sim_tick(sim, 0.0, &first, 1);
+
+    // Mid-animation second click → should not reset cutAnimStart.
+    sim_tick(sim, 0.05, nullptr, 0);  // 0.05 elapsed; cutHeight = 0.75
+    const double startSnapshot = sim.blades[0].cutAnimStart;
+    const double heightSnapshot = sim.blades[0].cutHeight;
+
+    InputEvent second = click(100.0, y, 0.05);
+    sim_tick(sim, 0.0, &second, 1);
+
+    REQUIRE(sim.blades[0].cutAnimStart    == Approx(startSnapshot));
+    REQUIRE(sim.blades[0].cutInitialHeight == Approx(1.0));
+    REQUIRE(sim.blades[0].cutHeight == Approx(heightSnapshot));
+}
+
+TEST_CASE("click on already-cut blade is a no-op", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0});
+    sim.blades[0].cutHeight        = 0.0;
+    sim.blades[0].cutInitialHeight = 0.0;
+    sim.blades[0].cutAnimStart     = -1.0;
+
+    const double y = sim.windowHeight - 40.0;
+    InputEvent ev = click(100.0, y, 0.0);
+    sim_tick(sim, 0.0, &ev, 1);
+
+    REQUIRE(sim.blades[0].cutHeight    == Approx(0.0));
+    REQUIRE(sim.blades[0].cutAnimStart  < 0.0);
+}
+
+TEST_CASE("blades outside cut radius are untouched", "[cut]") {
+    Sim sim = make_sim_with_blades({100.0, 131.0, 200.0});
+    const double y = sim.windowHeight - 40.0;
+
+    InputEvent ev = click(100.0, y, 0.0);
+    sim_tick(sim, 0.0, &ev, 1);
+
+    REQUIRE(sim.blades[0].cutAnimStart >= 0.0);
+    REQUIRE(sim.blades[1].cutAnimStart  < 0.0);
+    REQUIRE(sim.blades[2].cutAnimStart  < 0.0);
+}
+
+TEST_CASE("compute_blade_stroke degenerates to a stump under threshold", "[cut][geometry]") {
+    Blade b{};
+    b.baseX            = 100.0;
+    b.height           = 20.0;
+    b.thickness        = 1.5;
+    b.hue              = 2;
+    b.cutHeight        = 0.04;       // below CUT_STUMP_THRESHOLD = 0.05
+    b.effectiveLean    = 5.0;
+    b.cutInitialHeight = 1.0;
+    b.cutAnimStart     = 0.0;
+
+    Stroke s = compute_blade_stroke(b, 110.0, Scene::Grass);
+    REQUIRE(s.tip.x == Approx(100.0));
+    REQUIRE(s.tip.y == Approx(110.0 - STUMP_HEIGHT));
+    REQUIRE(s.argb  == PALETTE[2]);
+}
+
+TEST_CASE("compute_blade_stroke produces vertical line when lean is zero", "[cut][geometry]") {
+    Blade b{};
+    b.baseX         = 100.0;
+    b.height        = 20.0;
+    b.thickness     = 1.5;
+    b.hue           = 1;
+    b.cutHeight     = 1.0;
+    b.effectiveLean = 0.0;
+
+    Stroke s = compute_blade_stroke(b, 110.0, Scene::Grass);
+    REQUIRE(s.base.x    == Approx(100.0));
+    REQUIRE(s.base.y    == Approx(110.0));
+    REQUIRE(s.tip.x     == Approx(100.0));
+    REQUIRE(s.tip.y     == Approx(90.0));
+    REQUIRE(s.control.x == Approx(100.0));
+}
+
+// ---------------------------------------------------------------------------
+// Cut-floor (stubble) variation
+// ---------------------------------------------------------------------------
+
+TEST_CASE("generated blades get a per-blade cut floor within spec range", "[cut][floor]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 50);
+
+    for (const Blade& b : blades) {
+        REQUIRE(b.cutFloor >= CUT_FLOOR_MIN);
+        REQUIRE(b.cutFloor <  CUT_FLOOR_MAX);
+        // Stubble must render as a short blade, never a degenerate stump.
+        REQUIRE(b.cutFloor >= CUT_STUMP_THRESHOLD);
+    }
+
+    // The whole point is variation: not every blade settles at the same height.
+    bool varies = false;
+    for (std::size_t i = 1; i < blades.size(); ++i) {
+        if (blades[i].cutFloor != blades[0].cutFloor) { varies = true; break; }
+    }
+    REQUIRE(varies);
+}
+
+TEST_CASE("cut settles at the per-blade stubble floor, not flat zero", "[cut][floor]") {
+    Blade b{};
+    b.height           = 20.0;
+    b.thickness        = 1.5;
+    b.cutHeight        = 1.0;
+    b.cutInitialHeight = 1.0;
+    b.cutFloor         = 0.12;
+    b.cutAnimStart     = 0.0;
+
+    // Advance past the full cut duration.
+    advance_cut(b, CUT_DURATION_SEC + 0.01);
+
+    REQUIRE(b.cutHeight    == Approx(0.12));
+    REQUIRE(b.cutAnimStart == Approx(-1.0));
+}
+
+TEST_CASE("cut-down animation lerps toward the floor", "[cut][floor]") {
+    Blade b{};
+    b.height           = 20.0;
+    b.cutHeight        = 1.0;
+    b.cutInitialHeight = 1.0;
+    b.cutFloor         = 0.10;
+    b.cutAnimStart     = 0.0;
+
+    // Half-way through the cut: lerp(1.0 -> 0.10) at t=0.5 = 0.10 + 0.90*0.5.
+    advance_cut(b, CUT_DURATION_SEC * 0.5);
+    REQUIRE(b.cutHeight == Approx(0.10 + 0.90 * 0.5).margin(1e-9));
+}
+
+TEST_CASE("regrowth grows back from the floor to full height", "[cut][floor][regrowth]") {
+    Blade b{};
+    b.height         = 20.0;
+    b.cutFloor       = 0.10;
+    b.cutHeight      = 0.10;
+    b.cutAnimStart   = -1.0;
+    b.regrowDuration = 0.4;
+    b.regrowStart    = 0.0;
+
+    // Half-way through regrowth: lerp(0.10 -> 1.0) at t=0.5.
+    advance_cut(b, 0.2);
+    REQUIRE(b.cutHeight == Approx(0.10 + 0.90 * 0.5).margin(1e-9));
+
+    // Fully regrown.
+    advance_cut(b, 0.4);
+    REQUIRE(b.cutHeight == Approx(1.0).margin(1e-9));
+}
+
+TEST_CASE("zero-floor blades still collapse fully (back-compat)", "[cut][floor]") {
+    Blade b{};
+    b.height           = 20.0;
+    b.cutHeight        = 1.0;
+    b.cutInitialHeight = 1.0;
+    b.cutFloor         = 0.0;
+    b.cutAnimStart     = 0.0;
+
+    advance_cut(b, CUT_DURATION_SEC + 0.01);
+    REQUIRE(b.cutHeight == Approx(0.0));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/desert_tests.cpp

@@ -0,0 +1,220 @@
+// desert_tests.cpp - §14 Desert scene cacti + tumbleweeds.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+#include "snapshot_data.h"
+
+#include <cmath>
+#include <cstddef>
+#include <vector>
+
+using namespace desktopgrass;
+
+namespace {
+
+constexpr double kMonitor1920 = 1920.0;
+
+struct ExpectedCactus {
+    std::size_t slotIndex = 0;
+    uint8_t type = 0;
+    double height = 0.0;
+    double width = 0.0;
+    int8_t armSide = +1;
+};
+
+ExpectedCactus first_expected_cactus(std::size_t bladeCount) {
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ CACTUS_PRNG_SALT);
+
+    for (std::size_t i = 0; i < bladeCount; ++i) {
+        const double r = prng_uniform(p, 0.0, 1.0);
+        if (r >= CACTUS_PROBABILITY) continue;
+
+        ExpectedCactus expected{};
+        expected.slotIndex = i;
+        expected.height = prng_uniform(p, CACTUS_HEIGHT_MIN, CACTUS_HEIGHT_MAX);
+        expected.width = prng_uniform(p, CACTUS_WIDTH_MIN, CACTUS_WIDTH_MAX);
+
+        const double armDraw = prng_uniform(p, 0.0, 1.0);
+        const double noArmThreshold = 1.0 - CACTUS_ARM_PROBABILITY;
+        const double twoArmThreshold = noArmThreshold + CACTUS_TWO_ARM_PROBABILITY * CACTUS_ARM_PROBABILITY;
+        if (armDraw < noArmThreshold) {
+            expected.type = 0;
+        } else if (armDraw < twoArmThreshold) {
+            expected.type = 2;
+        } else {
+            expected.type = 1;
+            expected.armSide = prng_uniform(p, 0.0, 1.0) < 0.5
+                ? static_cast<int8_t>(-1)
+                : static_cast<int8_t>(+1);
+        }
+        if (expected.height < CACTUS_ARM_MIN_HEIGHT) {
+            expected.type = 0;
+            expected.armSide = +1;
+        }
+        return expected;
+    }
+
+    FAIL("canonical seed produced no cactus slot");
+    return {};
+}
+
+int expected_tumbleweed_count(double monitorWidth) {
+    if (monitorWidth < 480.0) return 0;
+    int count = static_cast<int>(std::floor(monitorWidth / 1920.0 * static_cast<double>(TUMBLEWEED_COUNT_PER_1920DIP)));
+    return count < 1 ? 1 : count;
+}
+
+} // anonymous
+
+TEST_CASE("Desert constants are pinned", "[desert][constants]") {
+    REQUIRE(CACTUS_PROBABILITY == Approx(0.005));
+    REQUIRE(CACTUS_HEIGHT_MIN == Approx(30.0));
+    REQUIRE(CACTUS_HEIGHT_MAX == Approx(70.0));
+    REQUIRE(CACTUS_COLOR == 0xFF2D7A2Du);
+    REQUIRE(TUMBLEWEED_COUNT_PER_1920DIP == 4);
+    REQUIRE(TUMBLEWEED_SPEED_MAX == Approx(72.0));
+    REQUIRE(TUMBLEWEED_PRNG_SALT == 0x7B0117CA7B0117CAull);
+}
+
+TEST_CASE("sim_set_scene Desert clears entities and generates cacti", "[desert][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    Entity fake{};
+    fake.kind = EntityKind::Snowflake;
+    sim.entities.push_back(fake);
+
+    sim_set_scene(sim, Scene::Desert);
+
+    REQUIRE(sim.currentScene == Scene::Desert);
+    REQUIRE(sim.entities.size() == static_cast<std::size_t>(expected_tumbleweed_count(kMonitor1920)));
+    for (const Entity& e : sim.entities) REQUIRE(e.kind == EntityKind::Tumbleweed);
+
+    std::size_t cactusCount = 0;
+    for (const Blade& b : sim.blades) if (b.isCactus) ++cactusCount;
+    REQUIRE(cactusCount >= 1);
+    REQUIRE(cactusCount <= 10);
+}
+
+TEST_CASE("First cactus matches the spec-derived PRNG snapshot", "[desert][cactus]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    const ExpectedCactus expected = first_expected_cactus(sim.blades.size());
+
+    sim_set_scene(sim, Scene::Desert);
+
+    REQUIRE(expected.slotIndex < sim.blades.size());
+    const Blade& b = sim.blades[expected.slotIndex];
+    REQUIRE(b.isCactus);
+    REQUIRE(b.cactusType == expected.type);
+    REQUIRE(b.cactusHeight == Approx(expected.height).margin(1e-12));
+    REQUIRE(b.cactusWidth == Approx(expected.width).margin(1e-12));
+    if (expected.type == 1) REQUIRE(b.cactusArmSide == expected.armSide);
+}
+
+TEST_CASE("Grass scene restores original flower and mushroom slot variants", "[desert][restore]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    const ExpectedCactus expected = first_expected_cactus(sim.blades.size());
+    REQUIRE(expected.slotIndex < sim.blades.size());
+
+    Blade& target = sim.blades[expected.slotIndex];
+    target.isFlower = true;
+    target.isMushroom = true;
+    target.originalIsFlower = true;
+    target.originalIsMushroom = true;
+
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(sim.blades[expected.slotIndex].isCactus);
+    REQUIRE_FALSE(sim.blades[expected.slotIndex].isFlower);
+    REQUIRE_FALSE(sim.blades[expected.slotIndex].isMushroom);
+
+    sim_set_scene(sim, Scene::Grass);
+    REQUIRE_FALSE(sim.blades[expected.slotIndex].isCactus);
+    REQUIRE(sim.blades[expected.slotIndex].isFlower);
+    REQUIRE(sim.blades[expected.slotIndex].isMushroom);
+}
+
+TEST_CASE("Desert generates the expected tumbleweed count", "[desert][tumbleweed]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+
+    const int expected = expected_tumbleweed_count(kMonitor1920);
+    REQUIRE(expected >= 1);
+    REQUIRE(sim.entities.size() == static_cast<std::size_t>(expected));
+}
+
+TEST_CASE("First tumbleweed matches the spec-derived PRNG snapshot", "[desert][tumbleweed]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE_FALSE(sim.entities.empty());
+
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ TUMBLEWEED_PRNG_SALT);
+    const double expectedSize = prng_uniform(p, TUMBLEWEED_SIZE_MIN, TUMBLEWEED_SIZE_MAX);
+    const double expectedX = prng_uniform(p, 0.0, kMonitor1920);
+    const double expectedY = sim.windowHeight - prng_uniform(p, TUMBLEWEED_Y_OFFSET_MIN, TUMBLEWEED_Y_OFFSET_MAX);
+    const double speed = prng_uniform(p, TUMBLEWEED_SPEED_MIN, TUMBLEWEED_SPEED_MAX);
+    const double direction = prng_uniform(p, 0.0, 1.0) < 0.5 ? -1.0 : 1.0;
+    const double expectedVx = direction * speed;
+    const double expectedRotation = prng_uniform(p, 0.0, 6.28318530717958647692);
+
+    const Entity& e = sim.entities[0];
+    REQUIRE(e.kind == EntityKind::Tumbleweed);
+    REQUIRE(e.size == Approx(expectedSize).margin(1e-12));
+    REQUIRE(e.x == Approx(expectedX).margin(1e-12));
+    REQUIRE(e.y == Approx(expectedY).margin(1e-12));
+    REQUIRE(e.vx == Approx(expectedVx).margin(1e-12));
+    REQUIRE(e.rotation == Approx(expectedRotation).margin(1e-12));
+    REQUIRE(e.rotationSpeed == Approx(expectedVx / expectedSize).margin(1e-12));
+}
+
+TEST_CASE("Tumbleweed respawns at the opposite edge when off-screen", "[desert][tumbleweed]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE_FALSE(sim.entities.empty());
+
+    sim.entities[0].x = sim.monitorWidth + 100.0;
+    sim_tick_entities(sim, 0.0);
+
+    const Entity& e = sim.entities[0];
+    REQUIRE(e.kind == EntityKind::Tumbleweed);
+    REQUIRE(e.x == Approx(-e.size).margin(1e-12));
+    REQUIRE(e.vx > 0.0);
+}
+
+TEST_CASE("Tumbleweed hops above its baseline then settles", "[desert][tumbleweed]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE_FALSE(sim.entities.empty());
+
+    double yBase = sim.entities[0].altitudeAnchor;
+    REQUIRE(sim.entities[0].y == Approx(yBase).margin(1e-9)); // starts grounded
+
+    double minY = sim.entities[0].y;
+    for (int i = 0; i < 900; ++i) {
+        sim_tick_entities(sim, 1.0 / 60.0);
+        Entity& t = sim.entities[0];
+        // Pin x on-screen so it doesn't roll off and respawn mid-test.
+        if (t.x < 50.0) t.x = 50.0;
+        if (t.x > sim.monitorWidth - 50.0) t.x = sim.monitorWidth - 50.0;
+        yBase = t.altitudeAnchor;
+        minY = std::min(minY, t.y);
+        REQUIRE(t.y <= yBase + 1e-6); // never sinks below the baseline
+    }
+
+    REQUIRE(minY < yBase - 1.0); // it left the ground at least once
+}
+
+TEST_CASE("Desert scene leaves the canonical first blade geometry bit-identical", "[desert][snapshot]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, kMonitor1920, 1.0);
+    REQUIRE(sim.blades.size() == desktopgrass::test::CANONICAL_BLADE_COUNT);
+
+    sim_set_scene(sim, Scene::Desert);
+
+    const Blade& first = sim.blades[0];
+    const auto& expected = desktopgrass::test::CANONICAL_FIRST_10[0];
+    REQUIRE(first.baseX == Approx(expected.baseX).margin(1e-12));
+    REQUIRE(first.height == Approx(expected.height).margin(1e-12));
+    REQUIRE(first.thickness == Approx(expected.thickness).margin(1e-12));
+    REQUIRE(first.hue == expected.hue);
+    REQUIRE(first.swayPhaseOffset == Approx(expected.sway).margin(1e-12));
+    REQUIRE(first.stiffness == Approx(expected.stiffness).margin(1e-12));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/entity_skeleton_tests.cpp

@@ -0,0 +1,113 @@
+// entity_skeleton_tests.cpp
+//
+// Entity subsystem skeleton tests (architecture.md §13.2).
+//
+// Coverage:
+//   * EntityKind discriminants match the spec ({None=0, Tumbleweed=1,
+//     Snowflake=2}).
+//   * MAX_ENTITIES_PER_MONITOR is the locked cap (= 64).
+//   * sim_init defaults sim.entities to empty, capacity >= cap.
+//   * sim_set_scene clears entities (currently a no-op since the Grass
+//     scene generates none; §14/§15 add per-scene generators).
+//   * sim_tick_entities is safe on empty (no exceptions, no growth).
+//   * Tick on empty entities does not perturb other sim state (blades
+//     untouched, ambient PRNG untouched).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+using namespace desktopgrass;
+
+TEST_CASE("EntityKind has spec-locked discriminants", "[entities][enum]") {
+    REQUIRE(static_cast<int>(EntityKind::None)       == 0);
+    REQUIRE(static_cast<int>(EntityKind::Tumbleweed) == 1);
+    REQUIRE(static_cast<int>(EntityKind::Snowflake)  == 2);
+    REQUIRE(static_cast<int>(EntityKind::Sheep)      == 3);
+    REQUIRE(static_cast<int>(EntityKind::Cat)        == 4);
+    REQUIRE(static_cast<int>(EntityKind::Bunny)      == 6);
+    REQUIRE(static_cast<int>(EntityKind::Butterfly)  == 7);
+    REQUIRE(static_cast<int>(EntityKind::Firefly)    == 8);
+    REQUIRE(static_cast<int>(EntityKind::Bird)       == 9);
+    REQUIRE(MAX_ENTITIES_PER_MONITOR == 64);
+}
+
+TEST_CASE("sim_init reserves entities capacity", "[entities][init]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, DEFAULT_DENSITY);
+    REQUIRE(sim.entities.empty());
+    REQUIRE(sim.entities.capacity() >= static_cast<std::size_t>(MAX_ENTITIES_PER_MONITOR));
+    REQUIRE(sim.entitySeed == CANONICAL_TEST_SEED);
+}
+
+TEST_CASE("sim_set_scene clears entities", "[entities][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, 1.0);
+    // Push a fake entity directly to verify scene-transition removal runs.
+    Entity fake{};
+    fake.kind = EntityKind::Tumbleweed;
+    fake.x = 100.0;
+    sim.entities.push_back(fake);
+    REQUIRE(sim.entities.size() == 1);
+
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(sim.entities.empty());
+    REQUIRE(sim.entities.capacity() >= static_cast<std::size_t>(MAX_ENTITIES_PER_MONITOR));
+}
+
+TEST_CASE("sim_tick_entities is a no-op on empty outside Grass", "[entities][tick]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, 1.0);
+    sim.currentScene = Scene::Desert;
+    const auto bladesBefore = sim.blades.size();
+    const auto prngBefore   = sim.ambientPrng.state;
+
+    sim_tick_entities(sim, 0.016);
+    sim_tick_entities(sim, 0.5);
+
+    REQUIRE(sim.entities.empty());
+    REQUIRE(sim.blades.size() == bladesBefore);
+    REQUIRE(sim.ambientPrng.state == prngBefore);
+}
+
+TEST_CASE("sim_tick_entities advances a populated entity", "[entities][tick]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, 1.0);
+    sim.currentScene = Scene::Desert;
+    Entity e{};
+    e.kind          = EntityKind::Tumbleweed;
+    e.x             = 100.0;
+    e.y             = 50.0;
+    e.vx            = 50.0;    // DIP/sec
+    e.vy            = 0.0;
+    e.size          = 10.0;
+    e.rotation      = 0.5;
+    e.rotationSpeed = 1.0;     // rad/sec
+    e.age           = 0.0;
+    e.lifetime      = -1.0;    // infinite
+    e.seed          = 0xDEADBEEF;
+    sim.entities.push_back(e);
+
+    const double dt = 0.5;
+    sim_tick_entities(sim, dt);
+
+    REQUIRE(sim.entities.size() == 1);
+    const Entity& after = sim.entities[0];
+    REQUIRE(after.x == Approx(100.0 + 50.0 * dt));
+    REQUIRE(after.y == Approx(50.0));
+    REQUIRE(after.rotation == Approx(0.5 + 1.0 * dt));
+    REQUIRE(after.age == Approx(0.0 + dt));
+    REQUIRE(after.kind == EntityKind::Tumbleweed);
+}
+
+TEST_CASE("sim_tick calls sim_tick_entities (wiring check)", "[entities][tick]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, 1920.0, 1.0);
+    sim.currentScene = Scene::Desert;
+    Entity e{};
+    e.kind = EntityKind::Snowflake;
+    e.x = 0.0; e.y = 0.0;
+    e.vx = 10.0; e.vy = 20.0;
+    e.size = 2.0;
+    e.age = 0.0; e.lifetime = 100.0;
+    sim.entities.push_back(e);
+
+    sim_tick(sim, 0.1, nullptr, 0);
+    REQUIRE(sim.entities.size() == 1);
+    REQUIRE(sim.entities[0].x == Approx(1.0));   // 10 * 0.1
+    REQUIRE(sim.entities[0].y == Approx(2.0));   // 20 * 0.1
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/firefly_tests.cpp

@@ -0,0 +1,195 @@
+// firefly_tests.cpp - §17.7 ambient Firefly tests.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+
+namespace {
+constexpr double Monitor1920 = 1920.0;
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+Sim build_grass_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    Sim sim = sim_init(seed, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Grass);
+    return sim;
+}
+
+int prng_count(Prng& side, int minCount, int maxCount) {
+    const double draw = prng_uniform(side, static_cast<double>(minCount), static_cast<double>(maxCount + 1));
+    int count = static_cast<int>(std::floor(draw));
+    if (count < minCount) count = minCount;
+    if (count > maxCount) count = maxCount;
+    return count;
+}
+} // namespace
+
+TEST_CASE("Firefly constants are pinned to spec values", "[firefly][constants]") {
+    REQUIRE(FIREFLY_COUNT_MIN == 3);
+    REQUIRE(FIREFLY_COUNT_MAX == 6);
+    REQUIRE(FIREFLY_DRIFT_SPEED_MIN == Approx(4.0));
+    REQUIRE(FIREFLY_DRIFT_SPEED_MAX == Approx(10.0));
+    REQUIRE(FIREFLY_BODY_RADIUS == Approx(1.2));
+    REQUIRE(FIREFLY_GLOW_RADIUS == Approx(5.0));
+    REQUIRE(FIREFLY_BLINK_PERIOD_MIN == Approx(1.4));
+    REQUIRE(FIREFLY_BLINK_PERIOD_MAX == Approx(2.6));
+    REQUIRE(FIREFLY_BLINK_DUTY == Approx(0.55));
+    REQUIRE(FIREFLY_BLINK_FADE == Approx(0.30));
+    REQUIRE(FIREFLY_DRIFT_FREQ_X == Approx(0.4));
+    REQUIRE(FIREFLY_DRIFT_FREQ_Y == Approx(0.6));
+    REQUIRE(FIREFLY_DRIFT_AMP_X == Approx(0.6));
+    REQUIRE(FIREFLY_DRIFT_AMP_Y == Approx(8.0));
+    REQUIRE(FIREFLY_ALTITUDE_MIN == Approx(8.0));
+    REQUIRE(FIREFLY_ALTITUDE_MAX == Approx(55.0));
+    REQUIRE(FIREFLY_BODY_COLOR == 0xFFFFEE88u);
+    REQUIRE(FIREFLY_GLOW_COLOR_RGB == 0xEEDD66u);
+    REQUIRE(FIREFLY_GLOW_ALPHA_MAX == 110);
+    REQUIRE(FIREFLY_BODY_ALPHA_MAX == 255);
+    REQUIRE(FIREFLY_PRNG_SALT == 0xF13EF1E7777ull);
+}
+
+TEST_CASE("Grass generation produces firefly count in range", "[firefly][gen]") {
+    for (uint64_t i = 0; i < 128; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = build_grass_sim(seed);
+        REQUIRE(count_kind(sim, EntityKind::Firefly) >= FIREFLY_COUNT_MIN);
+        REQUIRE(count_kind(sim, EntityKind::Firefly) <= FIREFLY_COUNT_MAX);
+    }
+}
+
+TEST_CASE("Fireflies are Grass scene only", "[firefly][scene]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(count_kind(sim, EntityKind::Firefly) == 0);
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(count_kind(sim, EntityKind::Firefly) == 0);
+}
+
+TEST_CASE("Generated fireflies have speed altitude and blink period ranges", "[firefly][gen]") {
+    Sim sim = build_grass_sim();
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Firefly) continue;
+        REQUIRE(e.baseSpeed >= FIREFLY_DRIFT_SPEED_MIN);
+        REQUIRE(e.baseSpeed <  FIREFLY_DRIFT_SPEED_MAX);
+        REQUIRE(e.altitudeAnchor >= FIREFLY_ALTITUDE_MIN);
+        REQUIRE(e.altitudeAnchor <  FIREFLY_ALTITUDE_MAX);
+        REQUIRE(e.blinkPeriod >= FIREFLY_BLINK_PERIOD_MIN);
+        REQUIRE(e.blinkPeriod <  FIREFLY_BLINK_PERIOD_MAX);
+    }
+}
+
+TEST_CASE("Firefly PRNG draw order matches side stream", "[firefly][prng]") {
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ FIREFLY_PRNG_SALT);
+    Sim sim = build_grass_sim();
+
+    const int expectedCount = prng_count(side, FIREFLY_COUNT_MIN, FIREFLY_COUNT_MAX);
+    REQUIRE(count_kind(sim, EntityKind::Firefly) == expectedCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Firefly) continue;
+        const double xFrac = prng_uniform(side, 0.0, 1.0);
+        const double yFrac = prng_uniform(side, 0.0, 1.0);
+        const uint64_t vxSign = prng_next_u64(side) & 1ull;
+        const double expectedDir = vxSign != 0ull ? 1.0 : -1.0;
+        const double expectedSpeed = prng_uniform(side, FIREFLY_DRIFT_SPEED_MIN, FIREFLY_DRIFT_SPEED_MAX);
+        const double expectedBlinkPeriod = prng_uniform(side, FIREFLY_BLINK_PERIOD_MIN, FIREFLY_BLINK_PERIOD_MAX);
+        const double expectedBlinkPhase = prng_uniform(side, 0.0, 1.0);
+        const double expectedPhaseY = prng_uniform(side, 0.0, 2.0 * 3.14159265358979323846);
+        const double expectedPhaseX = prng_uniform(side, 0.0, 2.0 * 3.14159265358979323846);
+        const double expectedAltitude = FIREFLY_ALTITUDE_MIN + yFrac * (FIREFLY_ALTITUDE_MAX - FIREFLY_ALTITUDE_MIN);
+        const double expectedVx = expectedDir * expectedSpeed * (1.0 + FIREFLY_DRIFT_AMP_X * std::sin(expectedPhaseX));
+
+        REQUIRE(e.x == Approx(xFrac * Monitor1920));
+        REQUIRE(e.altitudeAnchor == Approx(expectedAltitude));
+        REQUIRE(e.baseSpeed == Approx(expectedSpeed));
+        REQUIRE(e.blinkPeriod == Approx(expectedBlinkPeriod));
+        REQUIRE(e.blinkPhase == Approx(expectedBlinkPhase));
+        REQUIRE(e.vx == Approx(expectedVx));
+        REQUIRE(e.phaseY == Approx(expectedPhaseY));
+        REQUIRE(e.phaseX == Approx(expectedPhaseX));
+        ++seen;
+    }
+    REQUIRE(seen == expectedCount);
+}
+
+TEST_CASE("Firefly edge wrap preserves altitude anchor", "[firefly][motion]") {
+    Sim sim = build_grass_sim();
+    auto it = std::find_if(sim.entities.begin(), sim.entities.end(), [](const Entity& e) { return e.kind == EntityKind::Firefly; });
+    REQUIRE(it != sim.entities.end());
+    const double margin = FIREFLY_GLOW_RADIUS;
+    it->x = Monitor1920 + margin + 1.0;
+    it->vx = std::abs(it->vx);
+    const double altitude = it->altitudeAnchor;
+    sim.currentScene = Scene::Desert;
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(it->x == Approx(-margin));
+    REQUIRE(it->altitudeAnchor == Approx(altitude));
+}
+
+TEST_CASE("Fireflies do not interact with cuts or pets", "[firefly][interaction]") {
+    Sim sim = sim_init(CANONICAL_TEST_SEED, Monitor1920, DEFAULT_DENSITY);
+    sim.entities.clear();
+    Entity firefly{};
+    firefly.kind = EntityKind::Firefly;
+    firefly.x = 500.0;
+    firefly.y = sim.windowHeight - STRIP_HEIGHT - 5.0;
+    firefly.vx = FIREFLY_DRIFT_SPEED_MIN;
+    firefly.baseSpeed = FIREFLY_DRIFT_SPEED_MIN;
+    firefly.altitudeAnchor = FIREFLY_ALTITUDE_MIN;
+    firefly.blinkPeriod = FIREFLY_BLINK_PERIOD_MIN;
+    firefly.lifetime = -1.0;
+    sim.entities.push_back(firefly);
+    Entity sheep{};
+    sheep.kind = EntityKind::Sheep;
+    sheep.x = firefly.x;
+    sheep.y = sim.windowHeight - SHEEP_BODY_HEIGHT - SHEEP_LEG_LENGTH;
+    sheep.vx = SHEEP_WALK_SPEED_MIN;
+    sheep.state = SHEEP_STATE_WALKING;
+    sheep.stateTimer = 10.0;
+    sim.entities.push_back(sheep);
+
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = firefly.x;
+    ev.y = firefly.y;
+    sim_apply_click(sim, ev);
+
+    REQUIRE(sim.entities[0].kind == EntityKind::Firefly);
+    REQUIRE(sim.entities[0].baseSpeed == Approx(FIREFLY_DRIFT_SPEED_MIN));
+    REQUIRE(sim.entities[1].state == SHEEP_STATE_WALKING);
+    for (const Blade& b : sim.blades) REQUIRE(b.cutAnimStart < 0.0);
+}
+
+TEST_CASE("Firefly blink brightness has on and off phases", "[firefly][blink]") {
+    const double period = 2.0;
+    REQUIRE(firefly_blink_brightness(period * 0.25, period, 0.0) == Approx(1.0));
+    REQUIRE(firefly_blink_brightness(period * 0.80, period, 0.0) == Approx(0.0));
+}
+
+TEST_CASE("Firefly phases decorrelate visible brightness", "[firefly][blink]") {
+    const double period = 2.0;
+    const double phases[] = { 0.0, 0.0375, 0.075, 0.1125, 0.25, 0.80 };
+    std::vector<double> distinct;
+    for (double phase : phases) {
+        const double b = firefly_blink_brightness(0.0, period, phase);
+        bool seen = false;
+        for (double existing : distinct) {
+            if (std::fabs(existing - b) < 1e-6) { seen = true; break; }
+        }
+        if (!seen) distinct.push_back(b);
+    }
+    REQUIRE(distinct.size() >= 4);
+}
+

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/flower_tests.cpp

@@ -0,0 +1,54 @@
+// flower_tests.cpp
+//
+// Tests for §5 flower stream + §7 head-render contract.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+
+TEST_CASE("flower stream is deterministic for a given seed", "[flowers]") {
+    std::vector<Blade> a, b;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, a);
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, b);
+    REQUIRE(a.size() == b.size());
+    for (std::size_t i = 0; i < a.size(); ++i) {
+        REQUIRE(a[i].isFlower           == b[i].isFlower);
+        REQUIRE(a[i].flowerHeadColorIdx == b[i].flowerHeadColorIdx);
+        REQUIRE(a[i].flowerHeadRadius   == b[i].flowerHeadRadius);
+        REQUIRE(a[i].heightBonus        == b[i].heightBonus);
+    }
+}
+
+TEST_CASE("flower count is within 3-sigma of FLOWER_PROBABILITY", "[flowers]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 100);
+
+    std::size_t flowerCount = 0;
+    for (const Blade& b : blades) if (b.isFlower) ++flowerCount;
+
+    const double n   = static_cast<double>(blades.size());
+    const double p   = FLOWER_PROBABILITY;
+    const double mu  = n * p;
+    const double sd  = std::sqrt(n * p * (1.0 - p));
+    // 3-sigma tolerance keeps this test stable across spec-conformant
+    // PRNG sequences. For seed=0x6B6173746F, n=321 we expect ~12.84 with
+    // sd≈3.51, so [2,24] is the acceptable range.
+    REQUIRE(flowerCount >= static_cast<std::size_t>(std::floor(mu - 3.0 * sd)));
+    REQUIRE(flowerCount <= static_cast<std::size_t>(std::ceil(mu + 3.0 * sd)));
+}
+
+TEST_CASE("flower stream does not perturb the main stream", "[flowers][conformance]") {
+    // Regenerate blades and assert the main-stream fields match the
+    // canonical snapshot. This is implicitly covered by blade_gen_tests
+    // (the first/last 10 still match), but pin it here for clarity.
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 0);
+    REQUIRE(blades[0].baseX == Approx(4.941073726820111).margin(1e-12));
+    REQUIRE(blades[0].height == Approx(24.469991818248864).margin(1e-12));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/gust_tests.cpp

@@ -0,0 +1,164 @@
+// gust_tests.cpp
+//
+// Gust impulse model tests (architecture.md §8).
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <cmath>
+
+using namespace desktopgrass;
+
+namespace {
+
+Sim make_sim_with_blades(std::initializer_list<double> baseXs) {
+    Sim sim;
+    sim.windowHeight = STRIP_HEIGHT + HEADROOM;
+    for (double x : baseXs) {
+        Blade b{};
+        b.baseX            = x;
+        b.height           = 20.0;
+        b.thickness        = 1.5;
+        b.swayPhaseOffset  = 0.0;
+        b.stiffness        = 1.0;
+        b.cutHeight        = 1.0;
+        b.cutInitialHeight = 1.0;
+        b.cutAnimStart     = -1.0;
+        sim.blades.push_back(b);
+    }
+    return sim;
+}
+
+InputEvent move(double x, double y, double t) {
+    return InputEvent{ EventType::Move, x, y, t };
+}
+
+} // anonymous
+
+TEST_CASE("first move event is a baseline; no impulse", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double groundY = sim.windowHeight;
+    const double bandY   = groundY - 10.0; // in band
+
+    sim_apply_move(sim, move(100.0, bandY, 0.0));
+    REQUIRE(sim.blades[0].gustVelocity == Approx(0.0));
+    REQUIRE(sim.prevCursorTime == Approx(0.0));
+}
+
+TEST_CASE("a second move inside the band emits an impulse", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0, 200.0, 400.0});
+    const double bandY = sim.windowHeight - 10.0;
+
+    sim_apply_move(sim, move(  0.0, bandY, 0.0));
+    sim_apply_move(sim, move(100.0, bandY, 0.05));  // velocity = 2000 DIP/sec
+
+    // Blade at 100 is right under the cursor → max impulse.
+    // Expected magnitude:
+    //   capped = 2000 (≤ 4000 cap)
+    //   impulseMagnitude = 2000 * 0.003 = 6.0
+    //   smoothstep at distance 0 = 1.0
+    //   smoothstep at distance 100/150 (blade @ 200) = (1-2/3)² * (3 - 2*(1-2/3))
+    REQUIRE(sim.blades[0].gustVelocity == Approx(6.0).margin(1e-9));
+    // Blade outside radius (400, dist=300 > 150) → no impulse.
+    REQUIRE(sim.blades[2].gustVelocity == Approx(0.0));
+    REQUIRE(sim.blades[1].gustVelocity > 0.0);
+    REQUIRE(sim.blades[1].gustVelocity < 6.0);
+}
+
+TEST_CASE("impulse is signed by motion direction", "[gust]") {
+    Sim left  = make_sim_with_blades({100.0});
+    Sim right = make_sim_with_blades({100.0});
+
+    const double y = left.windowHeight - 10.0;
+    sim_apply_move(left,  move(200.0, y, 0.0));
+    sim_apply_move(left,  move(100.0, y, 0.05)); // moving left
+
+    sim_apply_move(right, move(  0.0, y, 0.0));
+    sim_apply_move(right, move(100.0, y, 0.05)); // moving right
+
+    REQUIRE(left.blades[0].gustVelocity  < 0.0);
+    REQUIRE(right.blades[0].gustVelocity > 0.0);
+    REQUIRE(std::fabs(left.blades[0].gustVelocity) ==
+            Approx(std::fabs(right.blades[0].gustVelocity)).margin(1e-9));
+}
+
+TEST_CASE("cursor speed is capped at MAX_CURSOR_SPEED", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y = sim.windowHeight - 10.0;
+
+    sim_apply_move(sim, move(0.0,      y, 0.0));
+    sim_apply_move(sim, move(100000.0, y, 0.05)); // velocity ≈ 2e6 DIP/sec
+
+    // capped magnitude = MAX_CURSOR_SPEED * IMPULSE_SCALE = 4000 * 0.003 = 12
+    // but the blade is at distance ~100k from cursor: outside radius → no impulse
+    REQUIRE(sim.blades[0].gustVelocity == Approx(0.0));
+}
+
+TEST_CASE("max impulse at the cursor equals capped magnitude", "[gust]") {
+    Sim sim = make_sim_with_blades({1000.0});
+    const double y = sim.windowHeight - 10.0;
+
+    sim_apply_move(sim, move(0.0,    y, 0.0));
+    sim_apply_move(sim, move(1000.0, y, 0.0001)); // velocity huge → saturates
+
+    // Saturated: cursor lands at x=1000 (blade), distance=0, smoothstep=1.0
+    REQUIRE(sim.blades[0].gustVelocity ==
+            Approx(MAX_CURSOR_SPEED * IMPULSE_SCALE).margin(1e-9));
+}
+
+TEST_CASE("moves outside the gust band don't emit impulses", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y_above_band = sim.windowHeight - STRIP_HEIGHT - HEADROOM - 20.0;
+
+    sim_apply_move(sim, move(  0.0, y_above_band, 0.0));
+    sim_apply_move(sim, move(100.0, y_above_band, 0.05));
+    REQUIRE(sim.blades[0].gustVelocity == Approx(0.0));
+}
+
+TEST_CASE("out-of-band move updates baseline; re-entry parity", "[gust]") {
+    Sim sim = make_sim_with_blades({700.0});
+    const double inBandY    = sim.windowHeight - 10.0;
+    const double outOfBandY = sim.windowHeight - STRIP_HEIGHT - HEADROOM - 20.0;
+
+    // t0 in-band: primes baseline (first event, no impulse).
+    sim_apply_move(sim, move(500.0, inBandY, 0.0));
+    // t1 out-of-band: updates baseline but emits no impulse.
+    sim_apply_move(sim, move(520.0, outOfBandY, 0.05));
+    REQUIRE(sim.prevCursorX    == Approx(520.0));
+    REQUIRE(sim.prevCursorTime == Approx(0.05));
+    REQUIRE(sim.blades[0].gustVelocity == Approx(0.0));
+
+    // t2 re-enter in-band: emits impulse off the out-of-band baseline.
+    sim_apply_move(sim, move(700.0, inBandY, 0.10));
+
+    const double dtEv  = std::max(0.10 - 0.05, 1.0 / 1000.0);
+    const double velX  = (700.0 - 520.0) / dtEv;
+    const double capped = std::max(-MAX_CURSOR_SPEED, std::min(velX, MAX_CURSOR_SPEED));
+    const double expected = capped * IMPULSE_SCALE; // distance 0 → smoothstep = 1
+    REQUIRE(sim.blades[0].gustVelocity == Approx(expected).margin(1e-9));
+}
+
+TEST_CASE("large time gap resets cursor baseline", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0});
+    const double y = sim.windowHeight - 10.0;
+
+    sim_apply_move(sim, move(  0.0, y, 0.0));
+    sim_apply_move(sim, move(500.0, y, 0.5));   // > CURSOR_REINIT_GAP_SEC (0.25)
+    REQUIRE(sim.blades[0].gustVelocity == Approx(0.0));
+}
+
+TEST_CASE("impulse falls off smoothly with distance", "[gust]") {
+    Sim sim = make_sim_with_blades({100.0, 130.0, 175.0, 200.0, 249.0, 251.0});
+    const double y = sim.windowHeight - 10.0;
+
+    sim_apply_move(sim, move(  0.0, y, 0.0));
+    sim_apply_move(sim, move(100.0, y, 0.05));
+
+    // Monotonic falloff: cursor at 100.
+    REQUIRE(sim.blades[0].gustVelocity > sim.blades[1].gustVelocity);
+    REQUIRE(sim.blades[1].gustVelocity > sim.blades[2].gustVelocity);
+    REQUIRE(sim.blades[2].gustVelocity > sim.blades[3].gustVelocity);
+    REQUIRE(sim.blades[3].gustVelocity > sim.blades[4].gustVelocity);
+    // Just outside radius (251 → distance 151 > 150) → zero.
+    REQUIRE(sim.blades[5].gustVelocity == Approx(0.0));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/hedgehog_tests.cpp

@@ -0,0 +1,371 @@
+// hedgehog_tests.cpp
+//
+// §17.9 Hedgehog critter tests. Mirrors Win2D HedgehogTests.cs.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <cwchar>
+
+using namespace desktopgrass;
+
+namespace {
+
+constexpr double Monitor1920 = 1920.0;
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+Sim build_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    return sim_init(seed, Monitor1920, DEFAULT_DENSITY);
+}
+
+Sim build_grass_sim(uint64_t seed = CANONICAL_TEST_SEED) {
+    Sim sim = build_sim(seed);
+    sim_set_scene(sim, Scene::Grass);
+    sim_set_critter(sim, CritterKind::Bunny);
+    return sim;
+}
+
+Entity hedgehog_entity(double x = 500.0, double vx = HEDGEHOG_WALK_SPEED_MIN) {
+    Entity e{};
+    e.kind = EntityKind::Hedgehog;
+    e.size = HEDGEHOG_BODY_RADIUS;
+    e.x = x;
+    e.y = STRIP_HEIGHT + HEADROOM - HEDGEHOG_BODY_HEIGHT - HEDGEHOG_LEG_LENGTH;
+    e.vx = vx;
+    e.vy = 0.0;
+    e.rotationSpeed = std::abs(vx);
+    e.lifetime = -1.0;
+    e.state = HEDGEHOG_STATE_WALKING;
+    e.stateTimer = HEDGEHOG_WALK_DURATION_MIN;
+    e.previousState = HEDGEHOG_STATE_WALKING;
+    return e;
+}
+
+InputEvent click_event(double x, double y) {
+    InputEvent ev{};
+    ev.type = EventType::Click;
+    ev.x = x;
+    ev.y = y;
+    ev.time = 0.0;
+    return ev;
+}
+
+int prng_count(Prng& side, int minCount, int maxCount) {
+    const double draw = prng_uniform(side, static_cast<double>(minCount), static_cast<double>(maxCount + 1));
+    int count = static_cast<int>(std::floor(draw));
+    if (count < minCount) count = minCount;
+    if (count > maxCount) count = maxCount;
+    return count;
+}
+
+void advance_sheep(Prng& side, int count) {
+    for (int i = 0; i < count; ++i) {
+        const double margin = SHEEP_BODY_RADIUS + 8.0;
+        (void)prng_uniform(side, margin, Monitor1920 - margin);
+        (void)prng_uniform(side, SHEEP_WALK_SPEED_MIN, SHEEP_WALK_SPEED_MAX);
+        (void)prng_uniform(side, 0.0, 1.0);
+        (void)prng_next_u32(side);
+        (void)prng_uniform(side, SHEEP_WALK_DURATION_MIN, SHEEP_WALK_DURATION_MAX);
+        (void)prng_index(side, static_cast<uint32_t>(sizeof(SHEEP_NAME_POOL) / sizeof(SHEEP_NAME_POOL[0])));
+    }
+}
+
+void advance_cats(Prng& side, int count) {
+    for (int i = 0; i < count; ++i) {
+        const double margin = CAT_BODY_RADIUS + 8.0;
+        (void)prng_uniform(side, margin, Monitor1920 - margin);
+        (void)prng_uniform(side, CAT_WALK_SPEED_MIN, CAT_WALK_SPEED_MAX);
+        (void)prng_uniform(side, 0.0, 1.0);
+        (void)prng_next_u32(side);
+        (void)prng_uniform(side, CAT_WALK_DURATION_MIN, CAT_WALK_DURATION_MAX);
+        (void)prng_index(side, static_cast<uint32_t>(sizeof(CAT_NAME_POOL) / sizeof(CAT_NAME_POOL[0])));
+        (void)prng_index(side, static_cast<uint32_t>(CAT_COAT_VARIANT_COUNT));
+    }
+}
+
+void advance_bunnies(Prng& side, int count) {
+    for (int i = 0; i < count; ++i) {
+        (void)prng_uniform(side, 0.0, 1.0);
+        (void)prng_next_u64(side);
+        (void)prng_uniform(side, BUNNY_HOP_SPEED_MIN, BUNNY_HOP_SPEED_MAX);
+        (void)prng_index(side, static_cast<uint32_t>(sizeof(BUNNY_NAME_POOL) / sizeof(BUNNY_NAME_POOL[0])));
+    }
+}
+
+bool hedgehog_name_in_pool(const Entity& e) {
+    if (e.nameIndex >= sizeof(HEDGEHOG_NAME_POOL) / sizeof(HEDGEHOG_NAME_POOL[0])) return false;
+    const wchar_t* name = HEDGEHOG_NAME_POOL[e.nameIndex];
+    for (const wchar_t* candidate : HEDGEHOG_NAME_POOL) {
+        if (std::wcscmp(name, candidate) == 0) return true;
+    }
+    return false;
+}
+
+} // namespace
+
+TEST_CASE("Hedgehog constants are pinned to spec values", "[hedgehog][constants]") {
+    REQUIRE(HEDGEHOG_COUNT_MIN == 0);
+    REQUIRE(HEDGEHOG_COUNT_MAX == 1);
+    REQUIRE(HEDGEHOG_COUNT_PROBABILITY == Approx(0.55));
+    REQUIRE(HEDGEHOG_WALK_SPEED_MIN == Approx(4.0));
+    REQUIRE(HEDGEHOG_WALK_SPEED_MAX == Approx(8.0));
+    REQUIRE(HEDGEHOG_BODY_RADIUS == Approx(9.0));
+    REQUIRE(HEDGEHOG_BODY_HEIGHT == Approx(5.5));
+    REQUIRE(HEDGEHOG_HEAD_RADIUS == Approx(3.6));
+    REQUIRE(HEDGEHOG_NOSE_RADIUS == Approx(0.8));
+    REQUIRE(HEDGEHOG_LEG_LENGTH == Approx(2.5));
+    REQUIRE(HEDGEHOG_SPIKE_COUNT == 14);
+    REQUIRE(HEDGEHOG_SPIKE_LENGTH == Approx(3.0));
+    REQUIRE(HEDGEHOG_SPIKE_WIDTH == Approx(1.4));
+    REQUIRE(HEDGEHOG_SPIKE_ARC_START_DEG == Approx(-20.0));
+    REQUIRE(HEDGEHOG_SPIKE_ARC_END_DEG == Approx(200.0));
+    REQUIRE(HEDGEHOG_BODY_COLOR == 0xFF5C4633u);
+    REQUIRE(HEDGEHOG_SPIKE_COLOR == 0xFF3A2A1Fu);
+    REQUIRE(HEDGEHOG_SPIKE_TIP_COLOR == 0xFF1E150Eu);
+    REQUIRE(HEDGEHOG_NOSE_COLOR == 0xFF1A1208u);
+    REQUIRE(HEDGEHOG_EYE_COLOR == 0xFF1A1208u);
+    REQUIRE(HEDGEHOG_STATE_WALKING == 0);
+    REQUIRE(HEDGEHOG_STATE_SNUFFLING == 1);
+    REQUIRE(HEDGEHOG_STATE_IDLE == 2);
+    REQUIRE(HEDGEHOG_STATE_SLEEPING == 3);
+    REQUIRE(HEDGEHOG_STATE_CURLED == 4);
+    REQUIRE(HEDGEHOG_WALK_DURATION_MIN == Approx(6.0));
+    REQUIRE(HEDGEHOG_WALK_DURATION_MAX == Approx(12.0));
+    REQUIRE(HEDGEHOG_SNUFFLE_DURATION_MIN == Approx(3.0));
+    REQUIRE(HEDGEHOG_SNUFFLE_DURATION_MAX == Approx(6.0));
+    REQUIRE(HEDGEHOG_IDLE_DURATION_MIN == Approx(1.5));
+    REQUIRE(HEDGEHOG_IDLE_DURATION_MAX == Approx(3.0));
+    REQUIRE(HEDGEHOG_SLEEP_DURATION_MIN == Approx(10.0));
+    REQUIRE(HEDGEHOG_SLEEP_DURATION_MAX == Approx(25.0));
+    REQUIRE(HEDGEHOG_CURL_DURATION_MIN == Approx(3.0));
+    REQUIRE(HEDGEHOG_CURL_DURATION_MAX == Approx(5.5));
+    REQUIRE(HEDGEHOG_SNUFFLE_PROBABILITY == Approx(0.55));
+    REQUIRE(HEDGEHOG_IDLE_PROBABILITY == Approx(0.30));
+    REQUIRE(HEDGEHOG_SLEEP_PROB == Approx(0.50));
+    REQUIRE(HEDGEHOG_STARTLE_RADIUS == Approx(70.0));
+    REQUIRE(HEDGEHOG_SNUFFLE_HEAD_FREQ == Approx(5.0));
+    REQUIRE(HEDGEHOG_SNUFFLE_HEAD_AMP == Approx(0.7));
+    REQUIRE(HEDGEHOG_WADDLE_FREQ == Approx(4.0));
+    REQUIRE(HEDGEHOG_WADDLE_AMP == Approx(0.8));
+    REQUIRE(HEDGEHOG_ZZZ_CYCLE_SEC == Approx(SHEEP_ZZZ_CYCLE_SEC));
+    REQUIRE(HEDGEHOG_ZZZ_RISE == Approx(SHEEP_ZZZ_RISE * 0.5));
+    REQUIRE(HEDGEHOG_ZZZ_SIZE_START == Approx(SHEEP_ZZZ_SIZE_START * 0.6));
+    REQUIRE(HEDGEHOG_ZZZ_SIZE_END == Approx(SHEEP_ZZZ_SIZE_END * 0.6));
+    REQUIRE(sizeof(HEDGEHOG_NAME_POOL) / sizeof(HEDGEHOG_NAME_POOL[0]) == 12);
+    REQUIRE(std::wcscmp(HEDGEHOG_NAME_POOL[0], L"Bristle") == 0);
+    REQUIRE(std::wcscmp(HEDGEHOG_NAME_POOL[11], L"Burdock") == 0);
+}
+
+TEST_CASE("Hedgehog count distribution is probabilistic rare sighting", "[hedgehog][gen]") {
+    constexpr int N = 1000;
+    int present = 0;
+    for (uint64_t i = 0; i < N; ++i) {
+        const uint64_t seed = CANONICAL_TEST_SEED + i * 0x9E3779B97F4A7C15ull;
+        Sim sim = build_grass_sim(seed);
+        const int count = count_kind(sim, EntityKind::Hedgehog);
+        REQUIRE(count >= HEDGEHOG_COUNT_MIN);
+        REQUIRE(count <= HEDGEHOG_COUNT_MAX);
+        present += count;
+    }
+    REQUIRE(static_cast<double>(present) / N == Approx(HEDGEHOG_COUNT_PROBABILITY).margin(0.05));
+}
+
+TEST_CASE("Hedgehogs are Grass scene only", "[hedgehog][scene]") {
+    Sim sim = build_sim();
+    sim_set_scene(sim, Scene::Desert);
+    REQUIRE(count_kind(sim, EntityKind::Hedgehog) == 0);
+    sim_set_scene(sim, Scene::Winter);
+    REQUIRE(count_kind(sim, EntityKind::Hedgehog) == 0);
+}
+
+TEST_CASE("Generated hedgehogs have speed range", "[hedgehog][gen]") {
+    bool sawHedgehog = false;
+    for (uint64_t i = 0; i < 128; ++i) {
+        Sim sim = build_grass_sim(CANONICAL_TEST_SEED + i * 0xD1B54A32D192ED03ull);
+        for (const Entity& e : sim.entities) {
+            if (e.kind != EntityKind::Hedgehog) continue;
+            sawHedgehog = true;
+            REQUIRE(std::abs(e.vx) >= HEDGEHOG_WALK_SPEED_MIN);
+            REQUIRE(std::abs(e.vx) <= HEDGEHOG_WALK_SPEED_MAX);
+            REQUIRE(e.rotationSpeed == Approx(std::abs(e.vx)));
+        }
+    }
+    REQUIRE(sawHedgehog);
+}
+
+TEST_CASE("Generated hedgehogs have names in pool", "[hedgehog][gen]") {
+    bool sawHedgehog = false;
+    for (uint64_t i = 0; i < 128; ++i) {
+        Sim sim = build_grass_sim(CANONICAL_TEST_SEED + i * 0x94D049BB133111EBull);
+        for (const Entity& e : sim.entities) {
+            if (e.kind != EntityKind::Hedgehog) continue;
+            sawHedgehog = true;
+            REQUIRE(hedgehog_name_in_pool(e));
+        }
+    }
+    REQUIRE(sawHedgehog);
+}
+
+TEST_CASE("Hedgehog PRNG draw order follows sheep cats and bunnies", "[hedgehog][prng]") {
+    Prng side;
+    prng_init(side, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+    Sim sim = build_grass_sim();
+
+    const int sheepCount = prng_count(side, SHEEP_COUNT_MIN, SHEEP_COUNT_MAX);
+    advance_sheep(side, sheepCount);
+    const int catCount = prng_count(side, CAT_COUNT_MIN, CAT_COUNT_MAX);
+    advance_cats(side, catCount);
+    const int bunnyCount = prng_count(side, BUNNY_COUNT_MIN, BUNNY_COUNT_MAX);
+    advance_bunnies(side, bunnyCount);
+
+    const double hasDraw = prng_uniform(side, 0.0, 1.0);
+    const int hedgehogCount = hasDraw < HEDGEHOG_COUNT_PROBABILITY ? 1 : 0;
+    REQUIRE(count_kind(sim, EntityKind::Hedgehog) == hedgehogCount);
+
+    int seen = 0;
+    for (const Entity& e : sim.entities) {
+        if (e.kind != EntityKind::Hedgehog) continue;
+        const double margin = HEDGEHOG_BODY_RADIUS + 8.0;
+        const double xFrac = prng_uniform(side, 0.0, 1.0);
+        const double expectedX = margin + xFrac * (Monitor1920 - 2.0 * margin);
+        const uint64_t vxSign = prng_next_u64(side) & 1ull;
+        const double expectedDir = vxSign != 0ull ? 1.0 : -1.0;
+        const double expectedSpeed = prng_uniform(side, HEDGEHOG_WALK_SPEED_MIN, HEDGEHOG_WALK_SPEED_MAX);
+        const uint8_t expectedName = static_cast<uint8_t>(prng_index(side,
+            static_cast<uint32_t>(sizeof(HEDGEHOG_NAME_POOL) / sizeof(HEDGEHOG_NAME_POOL[0]))));
+        REQUIRE(e.x == Approx(expectedX));
+        REQUIRE(e.vx == Approx(expectedDir * expectedSpeed));
+        REQUIRE(e.nameIndex == expectedName);
+        ++seen;
+    }
+    REQUIRE(seen == hedgehogCount);
+}
+
+TEST_CASE("Hedgehog edge bounce flips direction", "[hedgehog][motion]") {
+    Sim sim = build_sim();
+    sim.currentScene = Scene::Desert;
+    sim.entities.clear();
+    Entity e = hedgehog_entity(Monitor1920 - (HEDGEHOG_BODY_RADIUS + 2.0) + 0.1, HEDGEHOG_WALK_SPEED_MIN);
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+
+    sim_tick_entities(sim, 0.016);
+
+    REQUIRE(sim.entities.front().vx < 0.0);
+}
+
+TEST_CASE("Hedgehog startle radius curls without flipping vx", "[hedgehog][click]") {
+    Sim sim = build_sim();
+    sim.entities.clear();
+    Entity e = hedgehog_entity(500.0, -HEDGEHOG_WALK_SPEED_MIN);
+    e.state = HEDGEHOG_STATE_WALKING;
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+
+    sim_apply_click(sim, click_event(e.x + 10.0, e.y));
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_CURLED);
+    REQUIRE(sim.entities.front().vx == Approx(-HEDGEHOG_WALK_SPEED_MIN));
+    REQUIRE(sim.entities.front().stateTimer >= HEDGEHOG_CURL_DURATION_MIN);
+    REQUIRE(sim.entities.front().stateTimer <= HEDGEHOG_CURL_DURATION_MAX);
+
+    Sim outside = build_sim();
+    outside.entities.clear();
+    Entity far = hedgehog_entity(500.0, HEDGEHOG_WALK_SPEED_MIN);
+    outside.entities.push_back(far);
+    sim_apply_click(outside, click_event(far.x + HEDGEHOG_STARTLE_RADIUS + 10.0, far.y));
+    REQUIRE(outside.entities.front().state == HEDGEHOG_STATE_WALKING);
+    REQUIRE(outside.entities.front().vx == Approx(HEDGEHOG_WALK_SPEED_MIN));
+}
+
+TEST_CASE("Hedgehog curl auto uncurls to previous state", "[hedgehog][state]") {
+    Sim sim = build_sim();
+    sim.entities.clear();
+    Entity e = hedgehog_entity(500.0, HEDGEHOG_WALK_SPEED_MIN);
+    e.state = HEDGEHOG_STATE_IDLE;
+    e.stateTimer = 2.5;
+    sim.entities.push_back(e);
+
+    sim_apply_click(sim, click_event(e.x, e.y));
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_CURLED);
+    sim_tick_entities(sim, HEDGEHOG_CURL_DURATION_MAX + 0.1);
+
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_IDLE);
+    REQUIRE(sim.entities.front().vx == Approx(HEDGEHOG_WALK_SPEED_MIN));
+}
+
+TEST_CASE("Hedgehog wakes from sleep on startle and does not resume sleep", "[hedgehog][click]") {
+    Sim sim = build_sim();
+    sim.entities.clear();
+    Entity e = hedgehog_entity(500.0, HEDGEHOG_WALK_SPEED_MIN);
+    e.state = HEDGEHOG_STATE_SLEEPING;
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+
+    sim_apply_click(sim, click_event(e.x + 10.0, e.y));
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_CURLED);
+    REQUIRE(sim.entities.front().state != HEDGEHOG_STATE_SLEEPING);
+    sim_tick_entities(sim, HEDGEHOG_CURL_DURATION_MAX + 0.1);
+
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_WALKING);
+    REQUIRE(sim.entities.front().state != HEDGEHOG_STATE_SLEEPING);
+}
+
+TEST_CASE("Hedgehog state transition probabilities are stable", "[hedgehog][state]") {
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ CRITTER_PRNG_SALT);
+    constexpr int N = 10000;
+    int snuffle = 0;
+    int idle = 0;
+    int sleep = 0;
+    for (int i = 0; i < N; ++i) {
+        const uint8_t state = hedgehog_choose_rest_state(p);
+        if (state == HEDGEHOG_STATE_SNUFFLING) ++snuffle;
+        else if (state == HEDGEHOG_STATE_IDLE) ++idle;
+        else if (state == HEDGEHOG_STATE_SLEEPING) ++sleep;
+    }
+
+    const double sleepProb = HEDGEHOG_SLEEP_PROB;
+    const double activeWeight = HEDGEHOG_SNUFFLE_PROBABILITY + HEDGEHOG_IDLE_PROBABILITY;
+    const double expectedSnuffle = (1.0 - sleepProb) * HEDGEHOG_SNUFFLE_PROBABILITY / activeWeight;
+    const double expectedIdle = (1.0 - sleepProb) * HEDGEHOG_IDLE_PROBABILITY / activeWeight;
+    REQUIRE(static_cast<double>(sleep) / N == Approx(sleepProb).margin(0.02));
+    REQUIRE(static_cast<double>(snuffle) / N == Approx(expectedSnuffle).margin(0.02));
+    REQUIRE(static_cast<double>(idle) / N == Approx(expectedIdle).margin(0.02));
+}
+
+TEST_CASE("Hedgehog sleep probability is stable", "[hedgehog][state]") {
+    constexpr int N = 20000;
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ 0x1234ull);
+    int sleep = 0;
+    for (int i = 0; i < N; ++i) {
+        if (hedgehog_choose_rest_state(p) == HEDGEHOG_STATE_SLEEPING) ++sleep;
+    }
+    REQUIRE(static_cast<double>(sleep) / N == Approx(HEDGEHOG_SLEEP_PROB).margin(0.02));
+}
+
+TEST_CASE("Hedgehog has no active interaction states", "[hedgehog][state]") {
+    Prng p;
+    prng_init(p, CANONICAL_TEST_SEED ^ 0xCAFEull);
+    for (int i = 0; i < 1000; ++i) {
+        const uint8_t state = hedgehog_choose_rest_state(p);
+        REQUIRE((state == HEDGEHOG_STATE_SNUFFLING
+              || state == HEDGEHOG_STATE_IDLE
+              || state == HEDGEHOG_STATE_SLEEPING));
+    }
+
+    Sim sim = build_sim();
+    sim.entities.clear();
+    Entity e = hedgehog_entity(500.0, HEDGEHOG_WALK_SPEED_MIN);
+    e.stateTimer = 10.0;
+    sim.entities.push_back(e);
+    sim_tick_entities(sim, 0.016);
+    REQUIRE(sim.entities.front().state == HEDGEHOG_STATE_WALKING);
+    REQUIRE(std::abs(sim.entities.front().vx) == Approx(HEDGEHOG_WALK_SPEED_MIN));
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/main.cpp

@@ -0,0 +1,7 @@
+// main.cpp
+//
+// Catch2 entry point. The Sim.cpp translation unit is also linked in via the
+// vcxproj's source list so we can test it directly.
+
+#define CATCH_CONFIG_MAIN
+#include "../third_party/catch2/catch.hpp"

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/mushroom_tests.cpp

@@ -0,0 +1,89 @@
+// mushroom_tests.cpp
+//
+// Tests for §5 mushroom stream + §7 mushroom-render contract.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+#include <cmath>
+#include <vector>
+
+using namespace desktopgrass;
+
+TEST_CASE("mushroom stream is deterministic for a given seed", "[mushrooms]") {
+    std::vector<Blade> a, b;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, a);
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, b);
+    REQUIRE(a.size() == b.size());
+    for (std::size_t i = 0; i < a.size(); ++i) {
+        REQUIRE(a[i].isMushroom            == b[i].isMushroom);
+        REQUIRE(a[i].mushroomCapColorIdx   == b[i].mushroomCapColorIdx);
+        REQUIRE(a[i].mushroomCapWidth      == b[i].mushroomCapWidth);
+        REQUIRE(a[i].mushroomCapHeight     == b[i].mushroomCapHeight);
+        REQUIRE(a[i].mushroomStemHeight    == b[i].mushroomStemHeight);
+        REQUIRE(a[i].mushroomStemThickness == b[i].mushroomStemThickness);
+    }
+}
+
+TEST_CASE("mushroom count is within 3-sigma of MUSHROOM_PROBABILITY", "[mushrooms]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 100);
+
+    std::size_t mushroomCount = 0;
+    for (const Blade& b : blades) if (b.isMushroom) ++mushroomCount;
+
+    const double n   = static_cast<double>(blades.size());
+    const double p   = MUSHROOM_PROBABILITY;
+    const double mu  = n * p;
+    const double sd  = std::sqrt(n * p * (1.0 - p));
+    // 3-sigma tolerance keeps this test stable across spec-conformant
+    // PRNG sequences. For seed=0x6B6173746F, n=321 we expect ~8.03 with
+    // sd≈2.80, so the inclusive 3-sigma range is roughly [0, 17].
+    const double lo  = std::max(0.0, std::floor(mu - 3.0 * sd));
+    REQUIRE(mushroomCount >= static_cast<std::size_t>(lo));
+    REQUIRE(mushroomCount <= static_cast<std::size_t>(std::ceil(mu + 3.0 * sd)));
+}
+
+TEST_CASE("mushroom stream does not perturb the main stream", "[mushrooms][conformance]") {
+    // The mushroom stream is independent (seed ^ MUSHROOM_PRNG_SALT) so
+    // the main-stream first-blade values must still match the canonical.
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    REQUIRE(blades.size() > 0);
+    REQUIRE(blades[0].baseX == Approx(4.941073726820111).margin(1e-12));
+    REQUIRE(blades[0].height == Approx(24.469991818248864).margin(1e-12));
+}
+
+TEST_CASE("non-mushroom blades have zero mushroom fields", "[mushrooms]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    for (const Blade& b : blades) {
+        if (!b.isMushroom) {
+            REQUIRE(b.mushroomCapColorIdx   == 0);
+            REQUIRE(b.mushroomCapWidth      == 0.0);
+            REQUIRE(b.mushroomCapHeight     == 0.0);
+            REQUIRE(b.mushroomStemHeight    == 0.0);
+            REQUIRE(b.mushroomStemThickness == 0.0);
+        }
+    }
+}
+
+TEST_CASE("mushroom field ranges respect spec", "[mushrooms]") {
+    std::vector<Blade> blades;
+    generate_blades(CANONICAL_TEST_SEED, 1920.0, 1.0, blades);
+    for (const Blade& b : blades) {
+        if (b.isMushroom) {
+            REQUIRE(b.mushroomCapColorIdx < MUSHROOM_PALETTE_SIZE);
+            REQUIRE(b.mushroomCapWidth      >= MUSHROOM_CAP_WIDTH_MIN);
+            REQUIRE(b.mushroomCapWidth      <  MUSHROOM_CAP_WIDTH_MAX);
+            REQUIRE(b.mushroomCapHeight     >= MUSHROOM_CAP_HEIGHT_MIN);
+            REQUIRE(b.mushroomCapHeight     <  MUSHROOM_CAP_HEIGHT_MAX);
+            REQUIRE(b.mushroomStemHeight    >= MUSHROOM_STEM_HEIGHT_MIN);
+            REQUIRE(b.mushroomStemHeight    <  MUSHROOM_STEM_HEIGHT_MAX);
+            REQUIRE(b.mushroomStemThickness >= MUSHROOM_STEM_THICKNESS_MIN);
+            REQUIRE(b.mushroomStemThickness <  MUSHROOM_STEM_THICKNESS_MAX);
+        }
+    }
+}

src/modules/DesktopGrass/DesktopGrass.Native.Tests/src/ocean_tests.cpp

@@ -0,0 +1,114 @@
+// ocean_tests.cpp
+//
+// Ocean scene tests (architecture.md §17). Mirror of the Win2D OceanTests so
+// the coral blade variant, bubble emitter, and fish swimmers stay in lockstep
+// across impls.
+
+#include "../third_party/catch2/catch.hpp"
+#include "Sim.h"
+
+#include <algorithm>
+
+using namespace desktopgrass;
+
+namespace {
+
+constexpr double kMonitor1920 = 1920.0;
+
+Sim make_ocean_sim(uint64_t seed = CANONICAL_TEST_SEED,
+                   double width = kMonitor1920,
+                   double density = DEFAULT_DENSITY) {
+    Sim sim = sim_init(seed, width, density);
+    sim_set_scene(sim, Scene::Ocean);
+    return sim;
+}
+
+int count_kind(const Sim& sim, EntityKind kind) {
+    return static_cast<int>(std::count_if(sim.entities.begin(), sim.entities.end(),
+        [kind](const Entity& e) { return e.kind == kind; }));
+}
+
+} // namespace
+
+TEST_CASE("Ocean scene generates at least one coral and keeps values in range",
+          "[ocean][coral]") {
+    Sim sim = make_ocean_sim();
+
+    int coralCount = 0;
+    for (const Blade& b : sim.blades) {
+        if (!b.isCoral) continue;
+        ++coralCount;
+        REQUIRE_FALSE(b.isPine);
+        REQUIRE_FALSE(b.isCactus);
+        REQUIRE_FALSE(b.isMaple);
+        REQUIRE_FALSE(b.isFlower);
+        REQUIRE_FALSE(b.isMushroom);
+        REQUIRE(b.coralHeight >= CORAL_HEIGHT_MIN);
+        REQUIRE(b.coralHeight <= CORAL_HEIGHT_MAX);
+        REQUIRE(b.coralWidth  >= CORAL_WIDTH_MIN);
+        REQUIRE(b.coralWidth  <= CORAL_WIDTH_MAX);
+        REQUIRE(static_cast<int>(b.coralType)     >= 0);
+        REQUIRE(static_cast<int>(b.coralType)     <= CORAL_TYPE_COUNT  - 1);
+        REQUIRE(static_cast<int>(b.coralColorIdx) >= 0);
+        REQUIRE(static_cast<int>(b.coralColorIdx) <= CORAL_COLOR_COUNT - 1);
+    }
+    REQUIRE(coralCount > 0);
+}
+
+TEST_CASE("Ocean scene spawns initial fish at or above the target minimum",
+          "[ocean][fish]") {
+    Sim sim = make_ocean_sim();
+
+    const int fishCount = count_kind(sim, EntityKind::Fish);
+    REQUIRE(fishCount >= FISH_COUNT_MIN);
+    REQUIRE(fishCount <= FISH_COUNT_MAX);
+}
+
+TEST_CASE("Ocean fish count rounds half-to-even deterministically",
+          "[ocean][fish]") {
+    // scaled = 2.5 * width / 1920. Widths chosen so scaled lands exactly on a
+    // .5 tie; round-half-to-even must pick the even neighbor (NOT half-up),
+    // matching C# Math.Round and independent of the FPU rounding mode.
+    Sim tie25 = make_ocean_sim(CANONICAL_TEST_SEED, 1920.0); // scaled 2.5 -> 2
+    REQUIRE(count_kind(tie25, EntityKind::Fish) == 2);
+
+    Sim tie45 = make_ocean_sim(CANONICAL_TEST_SEED, 3456.0); // scaled 4.5 -> 4
+    REQUIRE(count_kind(tie45, EntityKind::Fish) == 4);
+}
+
+TEST_CASE("Ocean tick emits bubbles over time", "[ocean][bubble]") {
+    Sim sim = make_ocean_sim();
+
+    const double dt = 1.0 / 60.0;
+    for (int i = 0; i < 600; ++i) {
+        sim.globalTime += dt;
+        sim_tick_entities(sim, dt);
+    }
+
+    REQUIRE(count_kind(sim, EntityKind::Bubble) > 0);
+}
+
+TEST_CASE("Switching from Ocean to Grass wipes bubbles and fish",
+          "[ocean][scene]") {
+    Sim sim = make_ocean_sim();
+
+    const double dt = 1.0 / 60.0;
+    for (int i = 0; i < 120; ++i) {
+        sim.globalTime += dt;
+        sim_tick_entities(sim, dt);
+    }
+    REQUIRE(count_kind(sim, EntityKind::Fish) > 0);
+
+    sim_set_scene(sim, Scene::Grass);
+
+    REQUIRE(count_kind(sim, EntityKind::Bubble) == 0);
+    REQUIRE(count_kind(sim, EntityKind::Fish) == 0);
+    REQUIRE(std::none_of(sim.blades.begin(), sim.blades.end(),
+        [](const Blade& b) { return b.isCoral; }));
+}
+
+TEST_CASE("Ocean palette is pinned in scene palettes", "[ocean][palette]") {
+    for (int i = 0; i < PALETTE_SIZE; ++i) {
+        REQUIRE(SCENE_PALETTES[static_cast<int>(Scene::Ocean)][i] == OCEAN_PALETTE[i]);
+    }
+}