Fix the scene backdrop never rendering (issue #313) (#314)

* fix: render the scene backdrop through an object URL (issue #313)

* docs: state the disabled timeline actions as disabled in this version, no return promise

* fix: refuse unsafe and colliding save names when forking from a message

* fix: give fork_scene a real default save name instead of a missing method

* fix: slug the generated fork name so the guard cannot refuse it; pin the refusal messages

CHANGELOG.md

@@ -14,7 +14,7 @@ Chats can be made scene-aware, and each question carries a small snapshot of wha
 
 A new timeline dialog gives scene history a single home, replacing the old Restore from Backup dialog. Drag a slider across the scene's automatic version history to preview the message history at any revision, then fork that revision into a new save — the scene you are playing is never modified, and browsing the history changes nothing on disk.
 
-Forking is the only action the timeline applies in this version. Rolling a scene back in place and opening a revision directly are disabled while they are being reworked, and will return in a future version.
+Forking is the only action the timeline applies. Rolling a scene back in place and opening a revision directly are disabled in this version.
 
 ### Pi Bridge Client
 

CHANGELOG.yaml

@@ -33,11 +33,12 @@
   - "Scene Browser Landing Page: The Quick Load cards now pop out slightly on mouse hover, without shifting the cards around them."
   - "Prompt Finalization: UX polish for the post-processing actions editor — action fields lay out on a single balanced row with per-mode visibility (flags only show for exact and regex modes), each action card gained a compact header showing its mode and target plus tooltips on all controls, disabled actions dim their fields, an empty action list shows a hint instead of blank space."
   changes:
-  - "Timeline: Forking a revision to a new save is the only action the timeline applies in this release. Rolling a scene back in place and opening a revision directly are disabled while they are being reworked and will return in a future version — their websocket routes are gone, so no timeline action can write over an existing scene file. Browsing and previewing revisions are unaffected, and forking now refuses a save name that already exists instead of writing over it."
+  - "Timeline: Forking a revision to a new save is the only action the timeline applies in this release. Rolling a scene back in place and opening a revision directly are disabled in this version — their websocket routes are gone, so no timeline action can write over an existing scene file. Browsing and previewing revisions are unaffected, and forking now refuses a save name that already exists instead of writing over it."
   - "Dependencies: Refreshed the dependency lock across the board, including a setuptools bump to 83.0.0 which carries a fix for a source-distribution file-exclusion vulnerability (GHSA-h35f-9h28-mq5c). No dependency required code migrations."
   - "OpenRouter Client: The default model for newly created OpenRouter clients is now google/gemini-3.6-flash."
   - "OpenRouter Client: New OpenRouter clients now have reasoning enabled by default, with a budget of 2048 reasoning tokens, so the default model works out of the box. With reasoning off Talemate pre-fills the start of the response to steer it, and some providers — Google and Anthropic among them — reject requests that do that."
   fixes:
+  - "Scene Forking: Forking from a message now refuses a save name that is not a valid filename or that an existing save already uses, instead of writing over that save or outside the scene directory. The timeline fork already refused both."
   - "Prompt Finalization: The fuzzy match threshold slider's always-visible value bubble no longer overlaps the note above it."
   - "Frontend: A backend websocket URL configured with the host 0.0.0.0 now connects — the URL was used literally, which most browsers refuse, so the app stayed on 'backend not connected'. The host is resolved to the hostname the UI itself was loaded from."
   - "Help Chat: The warning shown while the Help agent has no configured client no longer stretches to fill the entire help panel — it renders as a compact notice above the chat."

docs/user-guide/restoring-scenes.md

@@ -6,7 +6,7 @@ Talemate provides two ways to return a scene to a previous state:
 - **Restore from Restore Point** — reset to a specific save file you've designated as a baseline in the [scene settings](/talemate/user-guide/world-editor/scene/settings#restoration-settings)
 
 !!! warning "The timeline only forks in this version"
-    Rolling a scene back in place and opening a revision directly are both disabled while they are being reworked, and will return in a future version. Forking a revision into a new save is the one action the timeline applies — it writes a new save alongside the scene and leaves every existing save untouched.
+    Rolling a scene back in place and opening a revision directly are both disabled in this version. Forking a revision into a new save is the one action the timeline applies — it writes a new save alongside the scene and leaves every existing save untouched.
 
 ## The timeline
 

src/talemate/agents/creator/assistant.py

@@ -1,5 +1,6 @@
 import json
 import re
+from datetime import datetime, timezone
 from typing import TYPE_CHECKING, Tuple
 import traceback
 import uuid
@@ -12,6 +13,7 @@ from talemate.emit import emit
 from talemate.instance import get_agent
 from talemate.prompts import Prompt
 from talemate.prompts.base import StripMode
+from talemate.util.path import is_safe_relative_filename
 from talemate.util.response import extract_list
 from talemate.scene_message import CharacterMessage
 from talemate.world_state.templates import (
@@ -808,12 +810,44 @@ class AssistantMixin:
 
         This properly creates a new scene file without modifying the current scene,
         then signals the frontend to load the new scene.
+
+        The fork always writes a save of its own: a name that is unsafe as a
+        filename, or that would land on an existing file, is refused rather
+        than escaping the save directory or overwriting a save. Without a
+        name it writes a timestamped one beside the scene, slugged so the
+        generated name cannot be the thing that gets refused.
         """
         try:
             emit("status", "Preparing to fork scene...", status="busy")
 
             if not save_name:
-                save_name = self.scene.generate_name()
+                # new scenes before their first save and restored scenes have
+                # no filename
+                base = (
+                    os.path.splitext(self.scene.filename)[0]
+                    if self.scene.filename
+                    else self.scene.project_name
+                )
+                stamp = datetime.now(timezone.utc).strftime("%Y%m%dT%H%M%SZ")
+                save_name = f"{util.slugify(base) or 'scene'}_fork_{stamp}"
+
+            fork_filename = f"{save_name}.json"
+
+            if not is_safe_relative_filename(fork_filename, suffix=".json"):
+                emit(
+                    "status",
+                    f"'{save_name}' is not a valid save name",
+                    status="error",
+                )
+                return
+
+            if os.path.exists(os.path.join(self.scene.save_dir, fork_filename)):
+                emit(
+                    "status",
+                    f"A save named '{save_name}' already exists — pick a different name",
+                    status="error",
+                )
+                return
 
             # Find the message to fork from
             message = self.scene.get_message(message_id)
@@ -889,7 +923,7 @@ class AssistantMixin:
                     scene_data["shared_context"] = ""
 
                 # Write the fork file
-                fork_file_path = os.path.join(self.scene.save_dir, f"{save_name}.json")
+                fork_file_path = os.path.join(self.scene.save_dir, fork_filename)
                 with open(fork_file_path, "w") as f:
                     json.dump(scene_data, f, indent=2, cls=SceneEncoder)
 

src/talemate/agents/help/docs-index.yaml

@@ -998,8 +998,7 @@
     history to preview any revision, then fork that revision into a new save; browsing and previewing write nothing to disk,
     and a save name an existing save already uses is refused) and restore from a designated restore point save file. Opened
     from the scene tools Save menu, a message's Fork button, or the scene card's three-dot menu. Forking is the timeline's
-    only action in this version — rolling a scene back in place and opening a revision directly are both disabled while they
-    are being reworked.
+    only action in this version — rolling a scene back in place and opening a revision directly are both disabled.
 - path: user-guide/saving.md
   title: Saving
   summary: How scene saving works, .json save files in the project directory, automatic changelog version history, restore

talemate_frontend/src/components/SceneMessages.vue

@@ -410,6 +410,7 @@ import { isVisualAgentReady, VIS_TYPE } from '@/constants/visual';
 import { isKnownSceneCharacter } from '@/utils/entityActions';
 import { parseCharacterMessage } from '@/utils/characterMessage.js';
 import { primaryModifierLabel } from '@/utils/keyboardModifiers';
+import { base64ToObjectUrl } from '@/utils/objectUrl.js';
 import {
     getMessageColor as resolveMessageColor,
     getMessageStyle as resolveMessageStyle,
@@ -616,6 +617,7 @@ export default {
             // cache (the asset may still be in flight when the dialog opens)
             assetViewShow: false,
             assetViewAssetId: null,
+            sceneBackdropObjectUrl: null,
         }
     },
     computed: {
@@ -651,8 +653,9 @@ export default {
         sceneBackdropAssetId() {
             return this.sceneBackdrop?.assetId || null;
         },
-        sceneBackdropSrc() {
-            return this.assetDataUrl(this.sceneBackdropAssetId);
+        sceneBackdropAsset() {
+            const assetId = this.sceneBackdropAssetId;
+            return assetId ? this.assetCache[assetId] || null : null;
         },
         // Most recent message-attached scene background the scene-tools
         // "Immersive" chip could promote to a backdrop when none is set yet
@@ -1336,6 +1339,26 @@ export default {
             return cached ? `data:${cached.mediaType};base64,${cached.base64}` : null;
         },
 
+        requestSceneBackdropAsset() {
+            const assetId = this.sceneBackdropAssetId;
+            if (assetId && this.requestSceneAssets && !this.assetCache[assetId]) {
+                this.requestSceneAssets([assetId]);
+            }
+        },
+
+        /**
+         * Swap in the backdrop's object URL, revoking the one it replaces.
+         * The backdrop reaches the DOM as a CSS custom property, and chromium
+         * silently drops custom property values over 2 MiB — which a scene
+         * image as a base64 data URL almost always exceeds.
+         */
+        setSceneBackdropObjectUrl(url) {
+            if (this.sceneBackdropObjectUrl) {
+                URL.revokeObjectURL(this.sceneBackdropObjectUrl);
+            }
+            this.sceneBackdropObjectUrl = url;
+        },
+
         showAssetMenu(event, context) {
             // Store the context (asset_id, asset_type, character, etc.)
             this.assetMenu.context = { ...context };
@@ -2170,14 +2193,29 @@ export default {
             },
             deep: true,
         },
-        sceneBackdropAssetId(assetId) {
-            if (assetId && this.requestSceneAssets && !this.assetCache[assetId]) {
-                this.requestSceneAssets([assetId]);
-            }
+        sceneBackdropAssetId: {
+            immediate: true,
+            handler() {
+                this.requestSceneBackdropAsset();
+            },
+        },
+        // Scene load empties the asset cache without changing the backdrop id,
+        // so the id watcher alone would leave a reloaded scene without its
+        // backdrop image.
+        sceneBackdropAsset: {
+            immediate: true,
+            handler(asset) {
+                this.setSceneBackdropObjectUrl(
+                    asset ? base64ToObjectUrl(asset.base64, asset.mediaType) : null
+                );
+                if (!asset) {
+                    this.requestSceneBackdropAsset();
+                }
+            },
         },
         // The backdrop is painted by TalemateApp behind the whole scene
         // column, so hand the resolved image up
-        sceneBackdropSrc: {
+        sceneBackdropObjectUrl: {
             immediate: true,
             handler(src) {
                 this.$emit('scene-backdrop', src);
@@ -2201,6 +2239,7 @@ export default {
             clearTimeout(this._reapplyDebounceTimer);
             this._reapplyDebounceTimer = null;
         }
+        this.setSceneBackdropObjectUrl(null);
     },
 }
 

talemate_frontend/src/components/SceneTimeline.vue

@@ -85,7 +85,7 @@
                     </v-alert>
 
                     <v-alert color="muted" icon="mdi-history" density="compact" variant="tonal" class="text-caption mt-3">
-                        Rolling a scene back in place and opening a revision directly are disabled in this version while they are being reworked, and will return in a future version. Fork the revision into a new save instead — it is written alongside the scene and leaves every existing save untouched.
+                        Rolling a scene back in place and opening a revision directly are disabled in this version. Fork the revision into a new save instead — it is written alongside the scene and leaves every existing save untouched.
                     </v-alert>
                 </template>
             </v-card-text>

talemate_frontend/src/components/TalemateApp.vue

@@ -531,7 +531,7 @@ export default {
   data() {
     return {
       appearancePreview: null, // Preview config while editing settings (null = use saved config)
-      // data-url of the scene illustration acting as the scene backdrop
+      // object URL of the scene illustration acting as the scene backdrop
       // (scene.assets.backdrop), reported up by SceneMessages which owns
       // the asset cache
       sceneBackdropSrc: null,

talemate_frontend/src/components/WhatsNew.vue

@@ -106,7 +106,7 @@ export default {
                         },
                         {
                             "title": "Timeline",
-                            "description": "A new timeline dialog gives scene history a single home, replacing the old Restore from Backup dialog. Drag a slider across the scene's automatic version history to preview the message history at any revision, then fork that revision into a new save — the scene you are playing is never modified, and browsing the history changes nothing on disk.\n\nForking is the only action the timeline applies in this version. Rolling a scene back in place and opening a revision directly are disabled while they are being reworked, and will return in a future version."
+                            "description": "A new timeline dialog gives scene history a single home, replacing the old Restore from Backup dialog. Drag a slider across the scene's automatic version history to preview the message history at any revision, then fork that revision into a new save — the scene you are playing is never modified, and browsing the history changes nothing on disk.\n\nForking is the only action the timeline applies. Rolling a scene back in place and opening a revision directly are disabled in this version."
                         },
                         {
                             "title": "Pi Bridge Client",

talemate_frontend/src/utils/objectUrl.js

@@ -0,0 +1,14 @@
+/**
+ * Turn base64 asset data into an object URL. Callers own the returned URL and
+ * must revoke it. Asset data is fine as a data URL on an <img>, but not in
+ * CSS: chromium silently drops custom property values over 2 MiB, which scene
+ * images exceed as base64.
+ */
+export function base64ToObjectUrl(base64, mediaType = 'image/png') {
+    const binary = window.atob(base64);
+    const bytes = new Uint8Array(binary.length);
+    for (let i = 0; i < binary.length; i++) {
+        bytes[i] = binary.charCodeAt(i);
+    }
+    return URL.createObjectURL(new Blob([bytes], { type: mediaType }));
+}

tests/test_creator_fork_scene.py

@@ -0,0 +1,153 @@
+"""
+Tests for the save-name guard on ``creator.fork_scene``.
+
+Forking from a message reaches this path with a user-typed name. Like the
+timeline fork, it must refuse a name that is unsafe as a filename or that
+would land on an existing save, rather than escaping the save directory or
+overwriting a save with forked data.
+"""
+
+import os
+import re
+
+import pytest
+
+import talemate.instance as instance
+from talemate.scene_message import NarratorMessage
+
+from conftest import MockClient, MockScene, bootstrap_engine
+
+
+class _ForkScene(MockScene):
+    """Real ``Scene`` with ``save_dir`` pointed at a tmp dir.
+
+    The parent exposes ``save_dir`` as a ``@property`` that joins the scenes
+    directory with the project name; shadowing it with a class-level plain
+    attribute lets the instance own it.
+    """
+
+    save_dir = None  # type: ignore[assignment]
+
+    def __init__(self, save_dir: str, **kwargs):
+        super().__init__(**kwargs)
+        self.save_dir = save_dir
+
+
+@pytest.fixture
+def creator(tmp_path):
+    bootstrap_engine()
+    scene = _ForkScene(save_dir=str(tmp_path))
+    # distinct from the name, so a test can tell which one a generated save
+    # name was built from
+    scene.filename = "test_scene.json"
+    scene.name = "Project Scene"
+    scene.history.append(NarratorMessage("the scene begins"))
+    agent = instance.get_agent("creator")
+    agent.client = MockClient("test_client")
+    agent.scene = scene
+    return agent
+
+
+@pytest.fixture
+def emitted(monkeypatch):
+    """Capture the agent's status emissions as ``(typ, message, kwargs)``."""
+    calls = []
+    monkeypatch.setattr(
+        "talemate.agents.creator.assistant.emit",
+        lambda typ, message=None, **kwargs: calls.append((typ, message, kwargs)),
+    )
+    return calls
+
+
+def assert_refused(emitted, message):
+    assert ("status", message, {"status": "error"}) in emitted
+
+
+@pytest.fixture
+def message_id(creator):
+    return creator.scene.history[0].id
+
+
+async def test_fork_writes_a_new_save(creator, message_id, tmp_path):
+    fork_path = await creator.fork_scene(message_id, save_name="forked")
+
+    assert fork_path == os.path.join(str(tmp_path), "forked.json")
+    assert os.path.exists(fork_path)
+
+
+@pytest.mark.parametrize("save_name", [None, ""])
+async def test_fork_without_a_name_writes_a_timestamped_save(
+    creator, message_id, tmp_path, save_name
+):
+    fork_path = await creator.fork_scene(message_id, save_name=save_name)
+
+    assert fork_path is not None
+    assert os.path.exists(fork_path)
+    assert re.fullmatch(
+        r"test-scene_fork_\d{8}T\d{6}Z\.json", os.path.basename(fork_path)
+    )
+
+
+async def test_fork_without_a_name_falls_back_to_the_project_name(
+    creator, message_id, tmp_path
+):
+    """New scenes before their first save, and restored scenes, have no
+    filename."""
+    creator.scene.filename = ""
+
+    fork_path = await creator.fork_scene(message_id)
+
+    assert fork_path is not None
+    assert os.path.exists(fork_path)
+    assert os.path.basename(fork_path).startswith("project-scene_fork_")
+
+
+@pytest.mark.parametrize(
+    "scene_name,expected_base",
+    [
+        ("Fate/Stay Night", "fate-stay-night"),
+        ("..", "scene"),
+    ],
+)
+async def test_fork_without_a_name_slugs_the_base(
+    creator, message_id, tmp_path, scene_name, expected_base
+):
+    """A scene name the guard would refuse must not make the no-name fork
+    impossible — the caller supplied nothing, so there is nothing to correct."""
+    creator.scene.filename = ""
+    creator.scene.name = scene_name
+
+    fork_path = await creator.fork_scene(message_id)
+
+    assert fork_path is not None
+    assert os.path.exists(fork_path)
+    assert re.fullmatch(
+        rf"{expected_base}_fork_\d{{8}}T\d{{6}}Z\.json", os.path.basename(fork_path)
+    )
+
+
+async def test_fork_refuses_a_name_that_escapes_the_save_dir(
+    creator, message_id, tmp_path, emitted
+):
+    outside = tmp_path.parent / "escaped.json"
+
+    assert await creator.fork_scene(message_id, save_name="../escaped") is None
+    assert not outside.exists()
+    assert_refused(emitted, "'../escaped' is not a valid save name")
+
+
+@pytest.mark.parametrize("save_name", ["nested/fork", "..", "with\x00nul"])
+async def test_fork_refuses_unsafe_names(creator, message_id, tmp_path, save_name):
+    assert await creator.fork_scene(message_id, save_name=save_name) is None
+    assert list(tmp_path.iterdir()) == []
+
+
+async def test_fork_refuses_an_existing_save(creator, message_id, tmp_path, emitted):
+    existing = tmp_path / "taken.json"
+    existing.write_text("original")
+
+    assert await creator.fork_scene(message_id, save_name="taken") is None
+    assert existing.read_text() == "original"
+    assert_refused(
+        emitted, "A save named 'taken' already exists — pick a different name"
+    )