fix(slack): slash commands broken in DM threads due to session key mismatch

plugins/platforms/slack/adapter.py

@@ -3364,6 +3364,7 @@ async def _handle_slack_message(
                     thread_ts=event_thread_ts,
                     user_id=user_id,
                     team_id=team_id,
+                    chat_type="dm" if is_dm else "group",
                 )
                 if (
                     not reply_to_bot_thread
@@ -3395,6 +3396,7 @@ async def _handle_slack_message(
             thread_ts=event_thread_ts,
             user_id=user_id,
             team_id=team_id,
+            chat_type="dm" if is_dm else "group",
         ):
             thread_context = await self._fetch_thread_context(
                 channel_id=channel_id,
@@ -4567,6 +4569,8 @@ def _has_active_session_for_thread(
         thread_ts: str,
         user_id: str,
         team_id: str = "",
+        *,
+        chat_type: str = "group",
     ) -> bool:
         """Check if there's an active session for a thread.
 
@@ -4577,6 +4581,14 @@ def _has_active_session_for_thread(
         construction — avoids the bug where manual key building didn't
         respect ``thread_sessions_per_user`` and ``group_sessions_per_user``
         settings correctly.
+
+        Args:
+            chat_type: The session chat type — ``"dm"`` for IM/MPIM
+                conversations, ``"group"`` for channels.  Must come from
+                the event-derived ``channel_type`` (``"im"``/``"mpim"``
+                → ``"dm"``) rather than being inferred from the channel
+                ID prefix, because MPIM IDs start with ``"G"``, not
+                ``"D"``.
         """
         session_store = getattr(self, "_session_store", None)
         if not session_store:
@@ -4588,7 +4600,7 @@ def _has_active_session_for_thread(
             source = SessionSource(
                 platform=Platform.SLACK,
                 chat_id=channel_id,
-                chat_type="group",
+                chat_type=chat_type,
                 user_id=user_id,
                 thread_id=thread_ts,
                 scope_id=team_id or None,

tests/gateway/test_slack_approval_buttons.py

@@ -731,6 +731,115 @@ def test_no_session_store(self):
         assert result is False
 
 
+class TestSessionKeyChatType:
+    """Test that _has_active_session_for_thread passes event-derived chat_type.
+
+    Regression for #39527: the old code hardcoded ``chat_type="group"``,
+    which produced wrong session keys for DM and MPIM threads.  The fix
+    passes the event-derived ``chat_type`` so ``build_session_key()``
+    constructs the correct key for every channel type.
+    """
+
+    def test_dm_thread_session_found(self):
+        """IM channel (D-prefix) with an active DM session is found."""
+        adapter = _make_adapter()
+        mock_store = MagicMock()
+        # DM sessions key: agent:main:slack:dm:D_CHANNEL:thread_ts
+        mock_store._entries = {
+            "agent:main:slack:dm:D0DMCHANNEL:2000.0": MagicMock()
+        }
+        mock_store._ensure_loaded = MagicMock()
+        mock_store.config = MagicMock()
+        mock_store.config.group_sessions_per_user = True
+        mock_store.config.thread_sessions_per_user = False
+        adapter._session_store = mock_store
+
+        result = adapter._has_active_session_for_thread(
+            channel_id="D0DMCHANNEL",
+            thread_ts="2000.0",
+            user_id="U_USER",
+            chat_type="dm",
+        )
+        assert result is True
+
+    def test_dm_thread_not_found_with_group_type(self):
+        """Without chat_type='dm', a DM session key would not match.
+
+        This is the exact bug that the old ``hardcoded "group"`` code caused:
+        the lookup builds ``group:…`` while the real session is ``dm:…``.
+        """
+        adapter = _make_adapter()
+        mock_store = MagicMock()
+        mock_store._entries = {
+            "agent:main:slack:dm:D0DMCHANNEL:2000.0": MagicMock()
+        }
+        mock_store._ensure_loaded = MagicMock()
+        mock_store.config = MagicMock()
+        mock_store.config.group_sessions_per_user = True
+        mock_store.config.thread_sessions_per_user = False
+        adapter._session_store = mock_store
+
+        # Default chat_type="group" should NOT find the DM session
+        result = adapter._has_active_session_for_thread(
+            channel_id="D0DMCHANNEL",
+            thread_ts="2000.0",
+            user_id="U_USER",
+        )
+        assert result is False
+
+    def test_mpim_thread_session_found(self):
+        """MPIM channel (G-prefix, treated as DM) with an active session is found.
+
+        MPIM channel IDs start with "G", not "D", so inferring chat_type
+        from the prefix would incorrectly classify this as "group".
+        """
+        adapter = _make_adapter()
+        mock_store = MagicMock()
+        # MPIM sessions key: agent:main:slack:dm:G_MPIM_CHANNEL:thread_ts
+        mock_store._entries = {
+            "agent:main:slack:dm:G0MPIMCHANNEL:3000.0": MagicMock()
+        }
+        mock_store._ensure_loaded = MagicMock()
+        mock_store.config = MagicMock()
+        mock_store.config.group_sessions_per_user = True
+        mock_store.config.thread_sessions_per_user = False
+        adapter._session_store = mock_store
+
+        result = adapter._has_active_session_for_thread(
+            channel_id="G0MPIMCHANNEL",
+            thread_ts="3000.0",
+            user_id="U_USER",
+            chat_type="dm",  # event-derived: mpim → dm
+        )
+        assert result is True
+
+    def test_mpim_thread_not_found_with_group_type(self):
+        """Without passing chat_type='dm', MPIM sessions are invisible.
+
+        This is the specific case the reviewer flagged: the old D-prefix
+        heuristic would classify G-prefixed MPIM channels as "group",
+        missing the DM session.
+        """
+        adapter = _make_adapter()
+        mock_store = MagicMock()
+        mock_store._entries = {
+            "agent:main:slack:dm:G0MPIMCHANNEL:3000.0": MagicMock()
+        }
+        mock_store._ensure_loaded = MagicMock()
+        mock_store.config = MagicMock()
+        mock_store.config.group_sessions_per_user = True
+        mock_store.config.thread_sessions_per_user = False
+        adapter._session_store = mock_store
+
+        # Default chat_type="group" → builds group key → no match
+        result = adapter._has_active_session_for_thread(
+            channel_id="G0MPIMCHANNEL",
+            thread_ts="3000.0",
+            user_id="U_USER",
+        )
+        assert result is False
+
+
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