fix(retrieval): fail open on registry resolution errors

tests/test_retrieval.py

@@ -566,6 +566,59 @@ def test_retrieve_unknown_project_hint_does_not_widen_or_filter(monkeypatch):
     assert [r.chunk_id for r in results] == ["chunk-a", "chunk-b"]
 
 
+def test_retrieve_fails_open_when_project_scope_resolution_fails(monkeypatch):
+    warnings = []
+
+    class FakeStore:
+        def query(self, query_embedding, top_k=10, where=None):
+            assert top_k == 2
+            return {
+                "ids": [["chunk-a", "chunk-b"]],
+                "documents": [["doc a", "doc b"]],
+                "metadatas": [[
+                    {
+                        "heading_path": "Overview",
+                        "source_file": "p04-gigabit/file.md",
+                        "tags": "[]",
+                        "title": "A",
+                        "document_id": "doc-a",
+                    },
+                    {
+                        "heading_path": "Overview",
+                        "source_file": "p05-interferometer/file.md",
+                        "tags": "[]",
+                        "title": "B",
+                        "document_id": "doc-b",
+                    },
+                ]],
+                "distances": [[0.2, 0.21]],
+            }
+
+    monkeypatch.setattr("atocore.retrieval.retriever.get_vector_store", lambda: FakeStore())
+    monkeypatch.setattr("atocore.retrieval.retriever.embed_query", lambda query: [0.0, 0.1])
+    monkeypatch.setattr(
+        "atocore.retrieval.retriever._existing_chunk_ids",
+        lambda chunk_ids: set(chunk_ids),
+    )
+    monkeypatch.setattr(
+        "atocore.retrieval.retriever.get_registered_project",
+        lambda project_name: (_ for _ in ()).throw(ValueError("registry overlap")),
+    )
+    monkeypatch.setattr(
+        "atocore.retrieval.retriever.log.warning",
+        lambda event, **kwargs: warnings.append((event, kwargs)),
+    )
+
+    results = retrieve("overview", top_k=2, project_hint="p04")
+
+    assert [r.chunk_id for r in results] == ["chunk-a", "chunk-b"]
+    assert {warning[0] for warning in warnings} == {
+        "project_scope_resolution_failed",
+        "project_match_boost_resolution_failed",
+    }
+    assert all("registry overlap" in warning[1]["error"] for warning in warnings)
+
+
 def test_retrieve_downranks_archive_noise_and_prefers_high_signal_paths(monkeypatch):
     class FakeStore:
         def query(self, query_embedding, top_k=10, where=None):