feat(matrix): add dm_auto_thread config for DM auto-threading

Adds MATRIX_DM_AUTO_THREAD env var (default: false) to control
auto-threading in DM rooms independently from channel auto-threading.

Closes #15398

gateway/platforms/matrix.py

@@ -18,6 +18,7 @@ Environment variables:
     MATRIX_REQUIRE_MENTION      Require @mention in rooms (default: true)
     MATRIX_FREE_RESPONSE_ROOMS  Comma-separated room IDs exempt from mention requirement
     MATRIX_AUTO_THREAD          Auto-create threads for room messages (default: true)
+    MATRIX_DM_AUTO_THREAD       Auto-create threads for DM messages (default: false)
     MATRIX_RECOVERY_KEY         Recovery key for cross-signing verification after device key rotation
     MATRIX_DM_MENTION_THREADS   Create a thread when bot is @mentioned in a DM (default: false)
 """
@@ -301,6 +302,9 @@ class MatrixAdapter(BasePlatformAdapter):
             "1",
             "yes",
         )
+        self._dm_auto_thread: bool = os.getenv(
+            "MATRIX_DM_AUTO_THREAD", "false"
+        ).lower() in ("true", "1", "yes")
         self._dm_mention_threads: bool = os.getenv(
             "MATRIX_DM_MENTION_THREADS", "false"
         ).lower() in ("true", "1", "yes")
@@ -1416,7 +1420,7 @@ class MatrixAdapter(BasePlatformAdapter):
             body = self._strip_mention(body)
 
         # Auto-thread.
-        if not is_dm and not thread_id and self._auto_thread:
+        if not thread_id and ((not is_dm and self._auto_thread) or (is_dm and self._dm_auto_thread)):
             thread_id = event_id
             self._threads.mark(thread_id)
 

hermes_cli/config.py

@@ -56,7 +56,7 @@ _EXTRA_ENV_KEYS = frozenset({
     "WHATSAPP_MODE", "WHATSAPP_ENABLED",
     "MATTERMOST_HOME_CHANNEL", "MATTERMOST_REPLY_MODE",
     "MATRIX_PASSWORD", "MATRIX_ENCRYPTION", "MATRIX_DEVICE_ID", "MATRIX_HOME_ROOM",
-    "MATRIX_REQUIRE_MENTION", "MATRIX_FREE_RESPONSE_ROOMS", "MATRIX_AUTO_THREAD",
+    "MATRIX_REQUIRE_MENTION", "MATRIX_FREE_RESPONSE_ROOMS", "MATRIX_AUTO_THREAD", "MATRIX_DM_AUTO_THREAD",
     "MATRIX_RECOVERY_KEY",
 })
 import yaml
@@ -1839,6 +1839,14 @@ OPTIONAL_ENV_VARS = {
         "category": "messaging",
         "advanced": True,
     },
+    "MATRIX_DM_AUTO_THREAD": {
+        "description": "Auto-create threads for DM messages in Matrix (default: false)",
+        "prompt": "Auto-create threads in DMs (true/false)",
+        "url": None,
+        "password": False,
+        "category": "messaging",
+        "advanced": True,
+    },
     "MATRIX_DEVICE_ID": {
         "description": "Stable Matrix device ID for E2EE persistence across restarts (e.g. HERMES_BOT)",
         "prompt": "Matrix device ID (stable across restarts)",

tests/gateway/test_matrix.py

@@ -2209,3 +2209,52 @@ class TestMatrixOnRoomMessageFilter:
         ev = self._mk_event(sender="@alice:example.org", body="hello bot")
         await self.adapter._on_room_message(ev)
         self.adapter._handle_text_message.assert_awaited_once()
+# ---------------------------------------------------------------------------
+# DM auto-thread
+# ---------------------------------------------------------------------------
+
+class TestMatrixDmAutoThread:
+    def setup_method(self):
+        self.adapter = _make_adapter()
+        self.adapter._is_dm_room = AsyncMock(return_value=True)
+        self.adapter._get_display_name = AsyncMock(return_value="Alice")
+        self.adapter._background_read_receipt = MagicMock()
+        # Disable require_mention so DMs pass gating
+        self.adapter._require_mention = False
+
+    @pytest.mark.asyncio
+    async def test_dm_auto_thread_enabled_creates_thread(self):
+        """When dm_auto_thread is True, DM messages get auto-threaded."""
+        self.adapter._dm_auto_thread = True
+
+        ctx = await self.adapter._resolve_message_context(
+            room_id="!dm:ex",
+            sender="@alice:ex",
+            event_id="$ev1",
+            body="hello",
+            source_content={"body": "hello"},
+            relates_to={},
+        )
+
+        assert ctx is not None
+        _body, _is_dm, _chat_type, thread_id, _display, _source = ctx
+        assert thread_id == "$ev1"
+
+    @pytest.mark.asyncio
+    async def test_dm_auto_thread_disabled_no_thread(self):
+        """When dm_auto_thread is False (default), DMs have no auto-thread."""
+        self.adapter._dm_auto_thread = False
+
+        ctx = await self.adapter._resolve_message_context(
+            room_id="!dm:ex",
+            sender="@alice:ex",
+            event_id="$ev2",
+            body="hello",
+            source_content={"body": "hello"},
+            relates_to={},
+        )
+
+        assert ctx is not None
+        _body, _is_dm, _chat_type, thread_id, _display, _source = ctx
+        assert thread_id is None
+