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_sprint186_map_first_geographic_explorer.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 import re
 
 from pathlib import Path
-from tests.frontend_contract import assert_calls, assert_mentions, assert_wired, read_map_workspace
+from tests.frontend_contract import assert_calls, assert_mentions, assert_wired, read_map_workspace, read_feature
 
 
 ROOT = Path(__file__).resolve().parents[2]
@@ -14,7 +14,7 @@ def read(path: str) -> str:
 
 
 def test_map_first_explorer_is_the_default_product_flow() -> None:
-    app = read("frontend/src/App.tsx")
+    app = read_feature("shell")
     workspace = read_map_workspace()
 
     assert "useState<WorkspaceKey>('map')" in app
@@ -69,7 +69,7 @@ def test_map_rectangle_drag_is_wired_to_automatic_analysis() -> None:
 
 
 def test_dataset_detail_responses_cannot_overwrite_the_latest_map_layer() -> None:
-    workflow = read("frontend/src/hooks/useDatasetWorkflow.ts")
+    workflow = read_feature("datasets")
 
     assert "const datasetDetailRequestSequence = useRef(0)" in workflow
     assert "const detailRequestId = ++datasetDetailRequestSequence.current" in workflow