scope frontend contracts to the feature, not to one file

93 test files read a single frontend source and asserted identifiers in it. The
MapWorkspace split showed what that costs: 24 tests went red for a move that
changed no behaviour at all. A contract belongs to the feature — a container,
its hooks, its domain layer — not to whichever file currently holds it.

232 read sites now resolve through read_feature(). The distinction that makes
this safe is direction: a *positive* contract ("this is wired") may widen,
because the identifier must still exist somewhere in the feature; a *negative*
one ("this component performs no transport") is a statement about one file, and
widening it would quietly weaken the check. The 73 single-file reads that
remain are exactly those, and a guard now enforces the rule for new tests.

Verified rather than assumed: of the 732 migrated positive assertions, 644 still
match exactly one module — as specific as before — and the other 86 already
spanned a container and its hook by nature. Two apparent misses are an artefact
of the checking regex reading an escaped newline literally.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

backend/tests/test_sprint107_map_selection_export.py

@@ -16,6 +16,7 @@ from app.schemas.export import ExportCreateResponse
 from app.services.export_service import ExportService
 from app.services.storage_service import StorageService
 from app.services.vector_feature_service import VectorFeatureService
+from tests.frontend_contract import read_feature
 
 
 ROOT = Path(__file__).resolve().parents[2]
@@ -287,9 +288,9 @@ def test_area_constrained_bbox_rejects_selection_outside_work_area() -> None:
 def test_frontend_exposes_map_selection_export_action() -> None:
     types = (ROOT / "frontend" / "src" / "types.ts").read_text(encoding="utf-8")
     exports_api = (ROOT / "frontend" / "src" / "services" / "api" / "exports.ts").read_text(encoding="utf-8")
-    export_hook = (ROOT / "frontend" / "src" / "hooks" / "useExportWorkflow.ts").read_text(encoding="utf-8")
-    map_workspace = (ROOT / "frontend" / "src" / "components" / "map" / "MapWorkspace.tsx").read_text(encoding="utf-8")
-    app = (ROOT / "frontend" / "src" / "App.tsx").read_text(encoding="utf-8")
+    export_hook = read_feature("exports")
+    map_workspace = read_feature("map_workspace")
+    app = read_feature("shell")
 
     assert "'vector_selection'" in types
     assert "bbox?: VectorSelectionBBox" in exports_api