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_sprint182_viewport_vector_delivery.py

@@ -4,6 +4,7 @@ import pytest
 from pydantic import ValidationError
 
 from app.schemas.operations import VectorSelectionBBox, VectorSelectionRequest
+from tests.frontend_contract import read_feature
 
 
 ROOT = Path(__file__).resolve().parents[2]
@@ -22,7 +23,7 @@ def test_vector_selection_contract_keeps_an_explicit_bounded_limit() -> None:
 def test_large_vector_delivery_uses_existing_postgis_bbox_contract() -> None:
     config = (ROOT / "frontend" / "src" / "config" / "vectorDelivery.ts").read_text(encoding="utf-8")
     viewport_hook = (ROOT / "frontend" / "src" / "hooks" / "useViewportVectorLayer.ts").read_text(encoding="utf-8")
-    dataset_hook = (ROOT / "frontend" / "src" / "hooks" / "useDatasetWorkflow.ts").read_text(encoding="utf-8")
+    dataset_hook = read_feature("datasets")
 
     assert "VECTOR_VIEWPORT_FEATURE_THRESHOLD = 5_000" in config
     assert "VECTOR_VIEWPORT_MIN_ZOOM = 14" in config
@@ -35,9 +36,9 @@ def test_large_vector_delivery_uses_existing_postgis_bbox_contract() -> None:
 
 
 def test_map_reports_viewport_and_does_not_refit_each_slice() -> None:
-    app = (ROOT / "frontend" / "src" / "App.tsx").read_text(encoding="utf-8")
+    app = read_feature("shell")
     geo_map = (ROOT / "frontend" / "src" / "components" / "GeoMap.tsx").read_text(encoding="utf-8")
-    workspace = (ROOT / "frontend" / "src" / "components" / "map" / "MapWorkspace.tsx").read_text(encoding="utf-8")
+    workspace = read_feature("map_workspace")
 
     assert "useViewportVectorLayer" in app
     assert "fitMapDataOnChange={!viewportVectorLayerActive}" in app