fix(gateway): gate stream commentary reply-to on platforms that need it

Discord interim commentary was replying to the user's trigger message on
every update (66fa6e41c4 added reply_to unconditionally for Buzz). Discord
uses native thread_id; only Buzz/Slack/Mattermost/Feishu need reply-to
anchoring for threading.

- Stream consumer _send_commentary checks adapter.platform.value
- Passes reply_to only for buzz/slack/mattermost/feishu
- Discord/Telegram commentary posts flat or threads via metadata

gateway/stream_consumer.py

@@ -2714,10 +2714,16 @@ class GatewayStreamConsumer:
             # duplicate (live finding, 2026-08-16 canary).
             _md = self._metadata_for_send(final=False) or {}
             _md["_interim_send"] = True
+            # Only pass reply_to for platforms that use reply-anchoring for
+            # threading. Discord/Telegram use native thread_id in metadata;
+            # passing reply_to on every commentary creates reply spam.
+            _plat = getattr(getattr(self.adapter, "platform", None), "value", None)
+            _platform_name = str(_plat or getattr(self.adapter, "name", "")).lower()
+            _needs_reply_anchor = _platform_name in ("buzz", "slack", "mattermost", "feishu")
             result = await self.adapter.send(
                 chat_id=self.chat_id,
                 content=text,
-                reply_to=self._initial_reply_to_id,
+                reply_to=self._initial_reply_to_id if _needs_reply_anchor else None,
                 metadata=_md,
             )
             # Note: do NOT set _already_sent = True here.