Improve issue triage product-label detection (#49905)

## Summary

Issues that put the module in a `[Module]` title prefix (a common
PowerToys convention) but omit the bug template's **"Area(s) with
issue?"** section were left **Unclassified** with no `Product-*` label —
e.g. #49899 *"[Screen Ruler] Settings crashes ..."* got no
`Product-Screen Ruler` label despite the title.

Root cause: product-label detection was purely deterministic and narrow.
`parse_area` (`.github/scripts/issue-triage/issue-context.py`) only read
the template area section or a 6-entry keyword map, and the agent prompt
instructed the model to copy that candidate verbatim (and send `None`
otherwise). The `[Module]` title convention was never consulted.

## Change (two layers)

**1. Deterministic title-prefix matching (primary).** Parse the leading
`[Module]` bracket(s) in the title and match against existing
`Product-*` labels; upgrade the detected area when the body has no area
signal. Fully deterministic and auditable — this alone fixes Screen
Ruler and every other bracketed title.

**2. Constrained AI fallback (secondary).** Expose the repo's
`Product-*` labels as `Available product labels` in the deterministic
evidence, and allow the agent — **only when the deterministic candidate
is `None`** — to select the single best-matching existing label. This is
safe because the publisher already validates the agent's `product_label`
against the real label set, so the agent can only ever **add a valid
existing label**, never invent one or remove/change others.

The workflow prompt is `{{#runtime-import}}`-ed from `issue-triage.md`,
so the lock file changes only by its `body_hash` (sync check);
recompiled with the repo's current gh-aw `v0.84.3` to avoid unrelated
version drift.

## Tests

New unit tests in `tests/test_issue_context.py`:
- `test_title_prefix_maps_to_existing_product_label`
- `test_available_product_labels_are_sorted_and_filtered`
- `test_prepare_labels_bracketed_title_without_area_section`

All 30 tests pass (`python -m unittest tests.test_issue_context`).

## Files
- `.github/scripts/issue-triage/issue-context.py` — title-prefix
detection, available-label list, wiring
- `.github/scripts/issue-triage/tests/test_issue_context.py` — new tests
- `.github/workflows/issue-triage.md` — prompt allows constrained
fallback
- `.github/workflows/issue-triage.lock.yml` — recompiled (`body_hash`
only)

Generated with the GitHub Copilot CLI.

Co-authored-by: niels9001 <niels9001@users.noreply.github.com>
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>
Copilot-Session: 26025067-259e-43e3-9dc7-a9fc4b5ba58b

.github/scripts/issue-triage/tests/test_issue_context.py

@@ -45,9 +45,16 @@ _No response_
 class FakeApi:
     repository = "owner/repo"
 
-    def __init__(self, results=None, comments=None, latest_release=None):
+    def __init__(
+        self,
+        results=None,
+        comments=None,
+        latest_release=None,
+        current_issue=None,
+    ):
         self.results = results or []
         self.comments = comments or []
+        self.current_issue = current_issue
         self.latest_release = latest_release or {
             "tag_name": "v0.100.2",
             "prerelease": False,
@@ -57,6 +64,9 @@ class FakeApi:
     def list_comments(self, _issue_number):
         return self.comments
 
+    def get_issue(self, _issue_number):
+        return self.current_issue
+
     def list_labels(self):
         return [{"name": "Product-Keyboard Manager"}]
 
@@ -272,6 +282,130 @@ class IssueContextTests(unittest.TestCase):
             "Product-General",
         )
 
+    def test_title_prefix_maps_to_existing_product_label(self):
+        labels = [{"name": "Product-Screen Ruler"}, {"name": "Product-FancyZones"}]
+        self.assertEqual(
+            CONTEXT.title_bracket_segments("[Screen Ruler] Settings crash"),
+            ["Screen Ruler"],
+        )
+        self.assertEqual(
+            CONTEXT.title_bracket_segments("[Screen Ruler][Settings] crash"),
+            ["Screen Ruler", "Settings"],
+        )
+        self.assertEqual(CONTEXT.title_bracket_segments("No brackets here"), [])
+        self.assertEqual(
+            CONTEXT.title_product_label("[Screen Ruler] Settings crash", labels),
+            "Product-Screen Ruler",
+        )
+        self.assertEqual(
+            CONTEXT.title_product_label("[Bug] something broke", labels),
+            "None",
+        )
+
+    def test_available_product_labels_are_sorted_and_filtered(self):
+        labels = [
+            {"name": "Product-Screen Ruler"},
+            {"name": "Needs-Triage"},
+            {"name": "Product-Awake"},
+        ]
+        self.assertEqual(
+            CONTEXT.available_product_labels(labels),
+            ["Product-Awake", "Product-Screen Ruler"],
+        )
+
+    def test_allowed_product_labels_require_explicit_issue_text(self):
+        labels = [
+            {"name": "Product-Screen Ruler"},
+            {"name": "Product-FancyZones"},
+            {"name": "Product-General"},
+        ]
+        self.assertEqual(
+            CONTEXT.allowed_product_labels(
+                "Ruler settings problem",
+                "The Screen Ruler overlay is misplaced.",
+                labels,
+                "None",
+            ),
+            ["Product-Screen Ruler"],
+        )
+
+    def test_prepare_labels_bracketed_title_without_area_section(self):
+        issue = {
+            "number": 42,
+            "title": "[Screen Ruler] Settings crashes on legacy units value",
+            "body": (
+                "## Description\n\nSettings crashes when leaving the Screen "
+                "Ruler page with a legacy measurement-unit value."
+            ),
+            "user": {"login": "alice"},
+            "labels": [],
+        }
+
+        class ScreenRulerApi(FakeApi):
+            def list_labels(self):
+                return [{"name": "Product-Screen Ruler"}]
+
+        context, _, should_process = CONTEXT.prepare(
+            {"action": "opened", "issue": issue},
+            ScreenRulerApi(),
+        )
+        self.assertTrue(should_process)
+        self.assertIn("Detected area: Screen Ruler", context)
+        self.assertIn("Candidate product label: Product-Screen Ruler", context)
+        self.assertIn(
+            "Allowed product label candidates: Product-Screen Ruler",
+            context,
+        )
+
+    def test_title_prefix_overrides_inferred_area_without_template_selection(self):
+        issue = {
+            "number": 42,
+            "title": "[Screen Ruler] FancyZones-style overlay is misplaced",
+            "body": "The FancyZones overlay comparison shows the ruler is misplaced.",
+            "user": {"login": "alice"},
+            "labels": [],
+        }
+
+        class ProductApi(FakeApi):
+            def list_labels(self):
+                return [
+                    {"name": "Product-FancyZones"},
+                    {"name": "Product-Screen Ruler"},
+                ]
+
+        context, _, _ = CONTEXT.prepare(
+            {"action": "opened", "issue": issue},
+            ProductApi(),
+        )
+        self.assertIn("Detected area: Screen Ruler", context)
+        self.assertIn("Candidate product label: Product-Screen Ruler", context)
+
+    def test_explicit_template_area_takes_precedence_over_title_prefix(self):
+        issue = {
+            "number": 42,
+            "title": "[Screen Ruler] FancyZones editor issue",
+            "body": (
+                "### Area(s) with issue?\n\nFancyZones\n\n"
+                "### Description\n\nThe FancyZones editor is misplaced."
+            ),
+            "user": {"login": "alice"},
+            "labels": [],
+        }
+
+        class ProductApi(FakeApi):
+            def list_labels(self):
+                return [
+                    {"name": "Product-FancyZones"},
+                    {"name": "Product-Screen Ruler"},
+                ]
+
+        context, _, _ = CONTEXT.prepare(
+            {"action": "opened", "issue": issue},
+            ProductApi(),
+        )
+        self.assertIn("Detected area: FancyZones", context)
+        self.assertIn("Candidate product label: Product-FancyZones", context)
+
     def test_context_redacts_report_attachment_urls(self):
         context = CONTEXT.render_context(
             {
@@ -413,6 +547,38 @@ class IssueContextTests(unittest.TestCase):
         self.assertEqual(normalized["issue"]["number"], 10)
         self.assertTrue(should_process)
 
+    def test_force_evidence_uses_current_issue_and_emits_allowlists(self):
+        stale_issue = {
+            "number": 10,
+            "title": "Old title",
+            "body": "",
+            "user": {"login": "alice"},
+            "labels": [],
+        }
+        current_issue = {
+            "number": 10,
+            "title": "Screen Ruler overlay problem",
+            "body": "The Screen Ruler overlay is misplaced.",
+            "user": {"login": "alice"},
+            "labels": [],
+        }
+
+        class VerificationApi(FakeApi):
+            def list_labels(self):
+                return [{"name": "Product-Screen Ruler"}]
+
+        _, normalized, should_process, evidence = CONTEXT.prepare_with_evidence(
+            {"action": "edited", "issue": stale_issue},
+            VerificationApi(current_issue=current_issue),
+            force_evidence=True,
+        )
+        self.assertTrue(should_process)
+        self.assertEqual(normalized["issue"]["title"], current_issue["title"])
+        self.assertEqual(
+            evidence["allowed_product_labels"],
+            ["Product-Screen Ruler"],
+        )
+
     def test_candidate_retrieval_only_returns_older_issues(self):
         issue = {
             "number": 10,