fix(evidence): retain referenced vector generations

harness/tests/test_corpus_pipeline.py

@@ -220,6 +220,36 @@ def test_explicit_gc_blocks_while_job_holds_corpus_writer_lock(tmp_path):
     assert candidate.store.active_generation() is not None
 
 
+def test_gc_preserves_vector_dependencies_of_retained_manifests(tmp_path):
+    vectors = Vectors()
+    one = item("one", "a")
+    first = pipeline(tmp_path, Source([(one, "stable")]), vectors=vectors, retain=2).run().generation
+    second = pipeline(
+        tmp_path, Source([(one, "stable"), (item("two", "b"), "two")]),
+        vectors=vectors, retain=2,
+    ).run().generation
+    third = pipeline(
+        tmp_path, Source([(one, "stable"), (item("two", "c"), "changed")]),
+        vectors=vectors, retain=2,
+    ).run().generation
+    assert CorpusStore(tmp_path / "corpus").list_generations() == [second, third]
+    assert first in vectors.list_evidence_generations("evidence")
+
+
+def test_active_searcher_without_active_fails_closed_for_evidence(tmp_path):
+    from types import SimpleNamespace
+    from tht.search.evidence import active_searcher
+
+    class Delegate:
+        def search(self, embedding, top_n=10, kinds=None, metadata_filter=None):
+            return ["legacy"]
+
+    cfg = SimpleNamespace(paths=SimpleNamespace(artifacts=tmp_path / "artifacts"))
+    wrapped = active_searcher(cfg, Delegate())
+    assert wrapped.search([1.0], kinds=["evidence"]) == []
+    assert wrapped.search([1.0], kinds=["memory"]) == ["legacy"]
+
+
 def test_unchanged_documents_skip_acquire_normalize_chunk_and_embed(tmp_path):
     one = item("one", "a")
     first_source = Source([(one, "hello")])