Address review: orphan fixture invariant, note shared prefs constraint on the marker

tests/script/test_helpers.py

@@ -2136,6 +2136,20 @@ def test_fixture_map_includes_shared_yaml_markers() -> None:
         )
 
 
+def test_no_orphan_integration_fixtures() -> None:
+    """Every fixture must reach CI test selection; an orphan selects nothing."""
+    helpers.get_fixture_to_test_files.cache_clear()
+    mapping = helpers.get_fixture_to_test_files()
+    fixtures_dir = (Path(__file__).parent.parent / "integration" / "fixtures").resolve()
+    # cache_init is covered via INTEGRATION_TESTS_TRIGGER_FILES instead
+    orphans = [
+        f.stem
+        for f in fixtures_dir.glob("*.yaml")
+        if f.stem != "cache_init" and f.stem not in mapping
+    ]
+    assert not orphans, f"fixtures invisible to CI test selection: {orphans}"
+
+
 def test_lpt_partition_balances_skewed_weights() -> None:
     """Heavy items spread across groups instead of clustering."""
     items = [f"i{n}" for n in range(6)]