fix(evidence): reconcile generations safely

harness/tests/l0/test_pgvector_store.py

@@ -79,6 +79,13 @@ def vector_configs():
                     f"GRANT INSERT, UPDATE ON vectors.{table} "
                     "TO vector_l0_writer, vector_l0_no_sequence"
                 )
+                if table == "evidence":
+                    connection.exec_driver_sql(
+                        "GRANT DELETE ON vectors.evidence TO vector_l0_writer"
+                    )
+                    connection.exec_driver_sql(
+                        "GRANT SELECT (kind, metadata) ON vectors.evidence TO vector_l0_writer"
+                    )
                 connection.exec_driver_sql(
                     f"GRANT SELECT (record_key, kind, content_hash) "
                     f"ON vectors.{table} TO vector_l0_writer, vector_l0_no_sequence"
@@ -118,6 +125,21 @@ def test_pgvector_round_trip_hash_and_upsert(store):
     assert store.search(["memory"], [0.8, 0.2], limit=1)[0].id == "record:a"
 
 
+def test_pgvector_lists_and_deletes_exact_evidence_generation(store):
+    generation = "gen:" + "a" * 32
+    value = VectorWriteRecord(
+        record=VectorRecord(
+            id="evidence-generation-a", kind="evidence", ref="doc:a", title="a",
+            content="content", metadata={"vector_generation": generation},
+        ),
+        embedding=[1.0, 0.0], content_hash="sha256:" + "a" * 64,
+    )
+    store.upsert("evidence", [value])
+    assert generation in store.list_evidence_generations("evidence")
+    assert store.delete_generation("evidence", generation) == 1
+    assert generation not in store.list_evidence_generations("evidence")
+
+
 def test_pgvector_search_filters_kinds_before_limit(store):
     store.upsert("memory", [_record("solved", [1.0, 0.0], kind="solved_question")])
     hits = store.search("memory".split(), [1.0, 0.0], limit=1, kinds=["memory"])