fix(evidence): retain referenced vector generations

harness/tht/search/evidence.py

@@ -36,8 +36,6 @@ class ActiveEvidenceSearcher:
 
 def active_searcher(cfg, delegate):
     corpus_root = cfg.paths.artifacts.parent / "corpus"
-    if not corpus_root.exists():
-        return delegate
     return ActiveEvidenceSearcher(CorpusStore(corpus_root), delegate)
 
 
@@ -59,15 +57,18 @@ def active_evidence_hits(store: CorpusStore, vector_store, embedding, *, limit:
 def resolve_evidence_file(
     store: CorpusStore, evidence_id: str, *, materialized_root=None,
 ) -> str:
-    manifest = store.active_manifest()
-    if manifest is None:
-        return ""
-    for document in manifest.documents:
-        frontmatter = document.metadata.get("frontmatter", {})
-        identifiers = {document.document_id, document.source_id, str(frontmatter.get("id", ""))}
-        if evidence_id in identifiers:
-            root = materialized_root or (store.root / "runtime")
-            filename = document.document_id.removeprefix("doc:") + ".md"
-            path = store.materialize_document(document.document_id, root / filename)
-            return str(path) if path else ""
+    with store.writer_lock():
+        manifest = store.active_manifest()
+        if manifest is None:
+            return ""
+        for document in manifest.documents:
+            frontmatter = document.metadata.get("frontmatter", {})
+            identifiers = {document.document_id, document.source_id, str(frontmatter.get("id", ""))}
+            if evidence_id in identifiers:
+                root = materialized_root or (store.root / "runtime")
+                filename = document.document_id.removeprefix("doc:") + ".md"
+                path = store.materialize_document(
+                    document.document_id, root / filename, generation=manifest.manifest_id,
+                )
+                return str(path) if path else ""
     return ""