fix(evidence): retain referenced vector generations

harness/tests/l0/test_pgvector_corpus_lifecycle.py

@@ -119,6 +119,8 @@ def test_real_pgvector_corpus_job_lifecycle(tmp_path, persistent_pgvector):
     source_root = tmp_path / "sources"
     source_root.mkdir()
     kept = source_root / "kept.md"
+    stable = source_root / "stable.md"
+    stable.write_text("unchanged dependency evidence", encoding="utf-8")
     removed = source_root / "removed.md"
     removed.write_text("removed evidence generation zero", encoding="utf-8")
 
@@ -208,6 +210,7 @@ def test_real_pgvector_corpus_job_lifecycle(tmp_path, persistent_pgvector):
     assert active_pack
     assert any("active fourth generation" in result.content for result in active_pack)
     assert all(removed_document.content not in result.content for result in active_pack)
+    assert any("unchanged dependency evidence" in result.content for result in active_pack)
     manifest = CorpusStore(tmp_path / "corpus").active_manifest()
     assert resolve_evidence_file(
         CorpusStore(tmp_path / "corpus"), removed_document_id,
@@ -229,7 +232,9 @@ def test_real_pgvector_corpus_job_lifecycle(tmp_path, persistent_pgvector):
     recreated_hits = ActiveEvidenceSearcher(
         CorpusStore(tmp_path / "corpus"), EvidenceDelegate(recreated)
     ).search(query, top_n=2, kinds=["evidence"])
-    assert recreated_hits and all(hit.metadata["vector_generation"] == resumed.generation for hit in recreated_hits)
+    active_dependencies = set(manifest.metadata["document_generations"].values())
+    assert recreated_hits
+    assert all(hit.metadata["vector_generation"] in active_dependencies for hit in recreated_hits)
 
     orphan = "gen:" + "f" * 32
     recreated.upsert("evidence", [VectorWriteRecord(
@@ -243,7 +248,8 @@ def test_real_pgvector_corpus_job_lifecycle(tmp_path, persistent_pgvector):
     final_pipeline = _pipeline(tmp_path, source_root, recreated)
     report = final_pipeline.gc(workspace_root=tmp_path)
     assert report["evicted"] == [orphan]
-    expected = set(generations[-2:])
-    assert set(CorpusStore(tmp_path / "corpus").list_generations()) == expected
-    assert set(recreated.list_evidence_generations("evidence")) == expected
+    expected_fs = set(generations[-2:])
+    assert set(CorpusStore(tmp_path / "corpus").list_generations()) == expected_fs
+    expected_vectors = expected_fs | {generations[0]}
+    assert set(recreated.list_evidence_generations("evidence")) == expected_vectors
     assert final_pipeline.gc(workspace_root=tmp_path)["evicted"] == []