From bb1e4d94bf7150179800063cc875399b1a780998 Mon Sep 17 00:00:00 2001
From: Devorun <130918800+devorun@users.noreply.github.com>
Date: Tue, 31 Mar 2026 14:57:28 +0300
Subject: [PATCH] fix(mattermost): resolve thread follow-ups and tool output
 leaks (#4221)

---
 gateway/platforms/mattermost.py | 20 +++++++++++++++++---
 1 file changed, 17 insertions(+), 3 deletions(-)

diff --git a/gateway/platforms/mattermost.py b/gateway/platforms/mattermost.py
index c134bb35da56..5ed36732820b 100644
--- a/gateway/platforms/mattermost.py
+++ b/gateway/platforms/mattermost.py
@@ -101,6 +101,8 @@ def __init__(self, config: PlatformConfig):
         self._SEEN_MAX = 2000
         self._SEEN_TTL = 300  # 5 minutes
 
+        self._known_threads: set[str] = set()
+
     # ------------------------------------------------------------------
     # HTTP helpers
     # ------------------------------------------------------------------
@@ -265,6 +267,10 @@ async def send(
         formatted = self.format_message(content)
         chunks = self.truncate_message(formatted, MAX_POST_LENGTH)
 
+        thread_root = reply_to
+        if not thread_root and metadata:
+            thread_root = metadata.get("thread_id")
+
         last_id = None
         for chunk in chunks:
             payload: Dict[str, Any] = {
@@ -272,8 +278,10 @@ async def send(
                 "message": chunk,
             }
             # Thread support: reply_to is the root post ID.
-            if reply_to and self._reply_mode == "thread":
-                payload["root_id"] = reply_to
+            if thread_root and self._reply_mode == "thread":
+                payload["root_id"] = thread_root
+                if hasattr(self, "_known_threads"):
+                    self._known_threads.add(thread_root)
 
             data = await self._api_post("posts", payload)
             if not data or "id" not in data:
@@ -625,13 +633,19 @@ async def _handle_ws_event(self, event: Dict[str, Any]) -> None:
                 for pattern in mention_patterns
             )
 
-            if require_mention and not is_free_channel and not has_mention:
+            thread_id = post.get("root_id") or None
+            bot_involved = thread_id and hasattr(self, "_known_threads") and thread_id in self._known_threads
+
+            if require_mention and not is_free_channel and not has_mention and not bot_involved:
                 logger.debug(
                     "Mattermost: skipping non-DM message without @mention (channel=%s)",
                     channel_id,
                 )
                 return
 
+            if thread_id and hasattr(self, "_known_threads"):
+                self._known_threads.add(thread_id)
+
             # Strip @mention from the message text so the agent sees clean input.
             if has_mention:
                 for pattern in mention_patterns: