feat(security): implement FW-N5, FW-N6, FW-N7 (HMAC-SHA256 protocol docs, auto-generate token, replay attack defense)

skills/tmux-agent-orchestrate-delegate-job/scripts/job_subscriber.py

@@ -63,6 +63,7 @@ class _Watcher:
         self.events: "queue.Queue[Tuple[str, Dict[str, Any]]]" = queue.Queue()
         self.expected = set(expected_job_ids)
         self.tokens = expected_tokens  # job_id -> expected auth_token (or None)
+        self.last_seq: Dict[str, int] = {jid: 0 for jid in expected_job_ids}
 
     def on_message(self, _client, _userdata, msg) -> None:
         # --- defensive parsing -------------------------------------------
@@ -87,6 +88,16 @@ class _Watcher:
         if not mqtt_common.verify_hmac(payload, expected_token):
             logger.warning("drop event for job %s: HMAC verify failed", jid)
             return
+        # --- replay attack defense: check monotonic sequence ---
+        seq = payload.get("seq")
+        if seq is None or not isinstance(seq, int):
+            logger.warning("drop event for job %s: missing or invalid seq", jid)
+            return
+        if seq <= self.last_seq.get(jid, 0):
+            logger.warning("drop event for job %s: seq %d is not monotonically increasing (last %d)",
+                           jid, seq, self.last_seq.get(jid, 0))
+            return
+        self.last_seq[jid] = seq
         # Persistent audit log from the *subscriber's* vantage point: every event
         # that survives defensive parsing is recorded here, including ones a
         # different host published. This is the external-observer record that