fix(retrieval): preserve project ids across unscoped ingest

tests/test_retrieval.py

@@ -458,6 +458,72 @@ def test_retrieve_project_scope_prefers_exact_project_id(monkeypatch):
     assert [r.chunk_id for r in results] == ["chunk-target", "chunk-global"]
 
 
+def test_retrieve_empty_project_id_falls_back_to_path_ownership(monkeypatch):
+    target_project = type(
+        "Project",
+        (),
+        {
+            "project_id": "p04-gigabit",
+            "aliases": ("p04", "gigabit"),
+            "ingest_roots": (),
+        },
+    )()
+    other_project = type(
+        "Project",
+        (),
+        {
+            "project_id": "p05-interferometer",
+            "aliases": ("p05", "interferometer"),
+            "ingest_roots": (),
+        },
+    )()
+
+    class FakeStore:
+        def query(self, query_embedding, top_k=10, where=None):
+            return {
+                "ids": [["chunk-target", "chunk-other"]],
+                "documents": [["target doc", "other doc"]],
+                "metadatas": [[
+                    {
+                        "heading_path": "Overview",
+                        "source_file": "p04-gigabit/status.md",
+                        "tags": "[]",
+                        "title": "Target",
+                        "project_id": "",
+                        "document_id": "doc-a",
+                    },
+                    {
+                        "heading_path": "Overview",
+                        "source_file": "p05-interferometer/status.md",
+                        "tags": "[]",
+                        "title": "Other",
+                        "project_id": "",
+                        "document_id": "doc-b",
+                    },
+                ]],
+                "distances": [[0.2, 0.19]],
+            }
+
+    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: target_project,
+    )
+    monkeypatch.setattr(
+        "atocore.retrieval.retriever.load_project_registry",
+        lambda: [target_project, other_project],
+    )
+
+    results = retrieve("mirror architecture", top_k=2, project_hint="p04")
+
+    assert [r.chunk_id for r in results] == ["chunk-target"]
+
+
 def test_retrieve_unknown_project_hint_does_not_widen_or_filter(monkeypatch):
     class FakeStore:
         def query(self, query_embedding, top_k=10, where=None):