fix(ntfy): prevent echo loop by tagging outgoing messages

When publish_topic equals the subscribe topic, the agent's own replies
are echoed back by ntfy as incoming messages, creating an infinite
reply spiral.

Fix: tag outgoing messages with X-Tags: hermes-agent header, and skip
incoming messages that carry this tag. This is zero-config — works
automatically regardless of topic configuration.

Fixes NousResearch/hermes-agent#34447

plugins/platforms/ntfy/adapter.py

@@ -81,6 +81,7 @@ DEDUP_WINDOW_SECONDS = 300
 DEDUP_MAX_SIZE = 1000
 RECONNECT_BACKOFF = [2, 5, 10, 30, 60]
 STREAM_TIMEOUT_SECONDS = 90  # ntfy keepalive default is 55s; give margin
+_ECHO_TAG = "hermes-agent"  # tag added to outgoing messages for echo-loop prevention
 
 
 def _build_auth_header(token: str) -> Dict[str, str]:
@@ -311,6 +312,12 @@ class NtfyAdapter(BasePlatformAdapter):
             logger.debug("[%s] Duplicate message %s, skipping", self.name, msg_id)
             return
 
+        # Echo-loop prevention: skip messages tagged by this adapter.
+        tags = event.get("tags") or []
+        if _ECHO_TAG in tags:
+            logger.debug("[%s] Skipping own message (echo tag)", self.name)
+            return
+
         text = (event.get("message") or "").strip()
         if not text:
             logger.debug("[%s] Empty message body, skipping", self.name)
@@ -387,7 +394,11 @@ class NtfyAdapter(BasePlatformAdapter):
 
         url = f"{self._server}/{publish_topic}"
         markdown_enabled = (self.config.extra or {}).get("markdown", False)
-        headers = {**self._auth_headers(), "Content-Type": "text/plain; charset=utf-8"}
+        headers = {
+            **self._auth_headers(),
+            "Content-Type": "text/plain; charset=utf-8",
+            "X-Tags": _ECHO_TAG,
+        }
         if markdown_enabled:
             headers["X-Markdown"] = "true"