fix(memory): sweep legacy orphaned message vectors

Repair vector rows left behind by older databases at store startup. Keep the existing single-statement delete path from main and avoid reintroducing the redundant batched helper.

synapse/memory/store.py

@@ -251,6 +251,8 @@ class PersistentMemoryStore:
             "DELETE FROM settings WHERE key IN ('anthropic_api_key', 'escalation_model')"
         )
 
+        self._sweep_orphan_msg_vectors(conn)
+
         conn.commit()
         conn.close()
 
@@ -788,6 +790,29 @@ class PersistentMemoryStore:
         except Exception:
             pass
 
+    def _sweep_orphan_msg_vectors(self, conn) -> None:
+        """One-time repair for databases written before delete_conversation
+        cleaned up after itself: drop vectors whose message is already gone."""
+        try:
+            ids = [r["message_id"] for r in conn.execute(
+                "SELECT v.message_id FROM message_vectors v "
+                "LEFT JOIN messages m ON m.id = v.message_id WHERE m.id IS NULL"
+            ).fetchall()]
+            if ids:
+                conn.execute(
+                    "DELETE FROM message_vectors WHERE message_id NOT IN "
+                    "(SELECT id FROM messages)"
+                )
+                if self.vec_enabled and conn.execute(
+                    "SELECT 1 FROM sqlite_master WHERE name = 'vec_messages'"
+                ).fetchone():
+                    for message_id in ids:
+                        conn.execute(
+                            "DELETE FROM vec_messages WHERE rowid = ?", (message_id,)
+                        )
+        except Exception:
+            pass
+
     def _backfill_vec_msgs(self, conn, dim: int) -> None:
         """Index any message_vectors rows missing from vec_messages."""
         try:
@@ -1215,4 +1240,4 @@ class PersistentMemoryStore:
 from ..nexus_config import MEMORY_DB
 
 DB_PATH = MEMORY_DB
-store = PersistentMemoryStore(DB_PATH)
+store = PersistentMemoryStore(DB_PATH)