diff --git a/gateway/run.py b/gateway/run.py
index a1d2246b73..a11315e825 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -30069,6 +30069,12 @@ class GatewayRunner(GatewayAuthorizationMixin, GatewayKanbanWatchersMixin, Gatew
                 and source.thread_id
                 and event_message_id
             )
+            or (
+                # Buzz has no native thread_id; threading is always via reply-to
+                # the triggering event id (channel clutter otherwise).
+                str(getattr(source.platform, "value", source.platform) or "").lower() == "buzz"
+                and event_message_id
+            )
             or _relay_prospective_thread_id
             else None
         )
diff --git a/gateway/stream_consumer.py b/gateway/stream_consumer.py
index f11fa43262..4fc33efd20 100644
--- a/gateway/stream_consumer.py
+++ b/gateway/stream_consumer.py
@@ -2712,11 +2712,12 @@ class GatewayStreamConsumer:
             # draft(final=true) — that would seal the live stream with
             # interim text and orphan the true final into a plain-send
             # duplicate (live finding, 2026-08-16 canary).
-            _md = dict(self.metadata) if self.metadata else {}
+            _md = self._metadata_for_send(final=False) or {}
             _md["_interim_send"] = True
             result = await self.adapter.send(
                 chat_id=self.chat_id,
                 content=text,
+                reply_to=self._initial_reply_to_id,
                 metadata=_md,
             )
             # Note: do NOT set _already_sent = True here.
diff --git a/plugins/platforms/buzz/adapter.py b/plugins/platforms/buzz/adapter.py
index d3ce59aa6e..a60e182c67 100644
--- a/plugins/platforms/buzz/adapter.py
+++ b/plugins/platforms/buzz/adapter.py
@@ -795,8 +795,13 @@ class BuzzAdapter(BasePlatformAdapter):
         if not content:
             return SendResult(success=False, error="Empty message")
         args = ["messages", "send", "--channel", str(chat_id), "--content", "-"]
+        # Prefer the stable thread anchor from metadata.thread_id (Slack-style),
+        # then metadata.reply_to_message_id (gateway stream consumer /
+        # progress sends), then the explicit reply_to argument.  Without
+        # reply_to_message_id, interim commentary posts flat in the channel.
+        meta = metadata or {}
         reply_target = self._resolve_reply_anchor(
-            (metadata or {}).get("thread_id") or reply_to
+            meta.get("thread_id") or meta.get("reply_to_message_id") or reply_to
         )
         if reply_target and self._reply_to_mode != "off":
             args += ["--reply-to", str(reply_target)]
diff --git a/tests/gateway/test_buzz_adapter.py b/tests/gateway/test_buzz_adapter.py
index 5993bccab9..e3830c54fd 100644
--- a/tests/gateway/test_buzz_adapter.py
+++ b/tests/gateway/test_buzz_adapter.py
@@ -899,6 +899,29 @@ class TestBuzzAdapterSend:
         args, _stdin = cli.calls[0]
         assert args[args.index("--reply-to") + 1] == "buzz-event-123"
 
+    @pytest.mark.asyncio
+    async def test_send_uses_metadata_reply_to_message_id(self):
+        """Gateway stream/progress pass reply anchors via metadata.
+
+        Without honoring reply_to_message_id, mid-turn commentary posts as
+        new top-level channel messages instead of thread replies.
+        """
+        adapter = _make_adapter()
+        adapter._channel_state[CHANNEL] = {"chat_type": "group", "last_ts": 0, "seen": {}}
+        cli = _ScriptedCli()
+        cli.script("messages", "send", {"accepted": True, "event_id": "evt-reply", "message": ""})
+        adapter._run_cli = cli
+
+        result = await adapter.send(
+            CHANNEL,
+            "threaded reply",
+            metadata={"reply_to_message_id": "root-event-abc"},
+        )
+        assert result.success is True
+        args, _stdin = cli.calls[0]
+        assert "--reply-to" in args
+        assert args[args.index("--reply-to") + 1] == "root-event-abc"
+
     @pytest.mark.asyncio
     async def test_send_prefers_stable_thread_root_over_latest_reply(self):
         adapter = _make_adapter()
@@ -917,6 +940,7 @@ class TestBuzzAdapterSend:
         assert args[args.index("--reply-to") + 1] == "stable-root"
 
 
+
     @pytest.mark.asyncio
     async def test_send_image_local_file_uses_file_flag(self, tmp_path):
         img = tmp_path / "shot.png"
diff --git a/tests/gateway/test_run_progress_topics.py b/tests/gateway/test_run_progress_topics.py
index da3dd2efc7..c955605070 100644
--- a/tests/gateway/test_run_progress_topics.py
+++ b/tests/gateway/test_run_progress_topics.py
@@ -1925,3 +1925,14 @@ class TestSlackReplyInThreadProgressRouting:
             event_message_id="1700000000.000100",
             reply_in_thread=False,
         ) is None
+
+    def test_buzz_uses_event_message_id_as_progress_thread(self):
+        """Buzz has no native thread_id; progress must reply-to the trigger."""
+        from gateway.run import _resolve_progress_thread_id
+
+        assert _resolve_progress_thread_id(
+            "buzz",
+            source_thread_id=None,
+            event_message_id="evt-trigger-001",
+            reply_in_thread=True,
+        ) == "evt-trigger-001"