fix(state): keep stored token_count when the agent flush row carries token_count=None

The agent flush row (_db_flush_row) always sets token_count, None for a replayed
message, so keying the keep on the key's absence missed the main production writer
and a digest-matched rewrite still nulled the stored count. Key it on the value.

agent/transcript_repair.py

@@ -155,8 +155,9 @@ def resolve_and_repair_transcript_batch(
             adopt = transcript_row_snapshot(target_row) != expected
             if not adopt:
                 serialized = serialize_message_fn(msg, float(target_row["timestamp"]))
-                if "token_count" not in msg:
-                    # Replay dicts never carry token_count; a missing key means "unknown", not NULL.
+                if serialized["token_count"] is None:
+                    # Replays never decode token_count (the agent flush row sets it to None): None means
+                    # "unknown", not NULL.
                     serialized = {**serialized, "token_count": target_row["token_count"]}
                 if any(target_row[column] != serialized[column] for column in _OWNED_COLUMNS):
                     _rewrite_row(conn, session_id, target_row, serialized)

tests/hermes_state/test_unaddressed_rewrite_identity.py

@@ -55,8 +55,10 @@ def test_mutated_replay_rewrites_its_original_row(db, include_row_ids, content,
     assert restored[0][MESSAGE_UID] == before[0]["message_uid"]
     assert (DB_ROW_SNAPSHOT in restored[0]) is not include_row_ids
 
-    # Real rewrite sites change the payload BEFORE clearing the persisted marker.
+    # Real rewrite sites change the payload BEFORE clearing the persisted marker. The agent flush row
+    # (session_persistence._db_flush_row) always carries the token_count key, None for a replay.
     restored[0]["content"] = "after repair"
+    restored[0]["token_count"] = None
     restored[0].pop(_DB_PERSISTED_MARKER, None)
 
     assert db.append_messages_batch(sid, restored) == 0