feat(matrix): add MATRIX_DM_MENTION_THREADS env var

When enabled, @mentioning the bot in a DM creates a thread (default:
false). Supports both env var and YAML config (matrix.dm_mention_threads).
6 new tests, docs updated.

From #6957

gateway/config.py

@@ -642,6 +642,8 @@ def load_gateway_config() -> GatewayConfig:
                     os.environ["MATRIX_FREE_RESPONSE_ROOMS"] = str(frc)
                 if "auto_thread" in matrix_cfg and not os.getenv("MATRIX_AUTO_THREAD"):
                     os.environ["MATRIX_AUTO_THREAD"] = str(matrix_cfg["auto_thread"]).lower()
+                if "dm_mention_threads" in matrix_cfg and not os.getenv("MATRIX_DM_MENTION_THREADS"):
+                    os.environ["MATRIX_DM_MENTION_THREADS"] = str(matrix_cfg["dm_mention_threads"]).lower()
 
     except Exception as e:
         logger.warning(

gateway/platforms/feishu.py

@@ -1190,6 +1190,8 @@ class FeishuAdapter(BasePlatformAdapter):
                 lambda data: self._on_reaction_event("im.message.reaction.deleted_v1", data)
             )
             .register_p2_card_action_trigger(self._on_card_action_trigger)
+            .register_p2_im_chat_member_bot_added_v1(self._on_bot_added_to_chat)
+            .register_p2_im_chat_member_bot_deleted_v1(self._on_bot_removed_from_chat)
             .build()
         )
 

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_MENTION_THREADS   Create a thread when bot is @mentioned in a DM (default: false)
 """
 
 from __future__ import annotations
@@ -1043,6 +1044,13 @@ class MatrixAdapter(BasePlatformAdapter):
                 if not self._is_bot_mentioned(body, formatted_body):
                     return
 
+        # DM mention-thread: when enabled, @mentioning bot in a DM creates a thread.
+        if is_dm and not thread_id:
+            dm_mention_threads = os.getenv("MATRIX_DM_MENTION_THREADS", "false").lower() in ("true", "1", "yes")
+            if dm_mention_threads and self._is_bot_mentioned(body, source_content.get("formatted_body")):
+                thread_id = event.event_id
+                self._track_thread(thread_id)
+
         # Strip mention from body when present (including in DMs).
         if self._is_bot_mentioned(body, source_content.get("formatted_body")):
             body = self._strip_mention(body)
@@ -1360,6 +1368,13 @@ class MatrixAdapter(BasePlatformAdapter):
                 if not self._is_bot_mentioned(body, formatted_body):
                     return
 
+        # DM mention-thread: when enabled, @mentioning bot in a DM creates a thread.
+        if is_dm and not thread_id:
+            dm_mention_threads = os.getenv("MATRIX_DM_MENTION_THREADS", "false").lower() in ("true", "1", "yes")
+            if dm_mention_threads and self._is_bot_mentioned(body, source_content.get("formatted_body")):
+                thread_id = event.event_id
+                self._track_thread(thread_id)
+
         # Strip mention from body when present (including in DMs).
         if self._is_bot_mentioned(body, source_content.get("formatted_body")):
             body = self._strip_mention(body)

tests/gateway/test_matrix_mention.py

@@ -436,6 +436,95 @@ class TestThreadPersistence:
         assert len(data) == 5
 
 
+# ---------------------------------------------------------------------------
+# DM mention-thread feature
+# ---------------------------------------------------------------------------
+
+
+@pytest.mark.asyncio
+async def test_dm_mention_thread_disabled_by_default(monkeypatch):
+    """Default (dm_mention_threads=false): DM with mention should NOT create a thread."""
+    monkeypatch.delenv("MATRIX_DM_MENTION_THREADS", raising=False)
+    monkeypatch.setenv("MATRIX_AUTO_THREAD", "false")
+
+    adapter = _make_adapter()
+    room = _make_room(member_count=2)
+    event = _make_event("@hermes:example.org help me", event_id="$dm1")
+
+    await adapter._on_room_message(room, event)
+    adapter.handle_message.assert_awaited_once()
+    msg = adapter.handle_message.await_args.args[0]
+    assert msg.source.thread_id is None
+
+
+@pytest.mark.asyncio
+async def test_dm_mention_thread_creates_thread(monkeypatch):
+    """MATRIX_DM_MENTION_THREADS=true: DM with @mention creates a thread."""
+    monkeypatch.setenv("MATRIX_DM_MENTION_THREADS", "true")
+    monkeypatch.setenv("MATRIX_AUTO_THREAD", "false")
+
+    adapter = _make_adapter()
+    room = _make_room(member_count=2)
+    event = _make_event("@hermes:example.org help me", event_id="$dm1")
+
+    with patch.object(adapter, "_save_participated_threads"):
+        await adapter._on_room_message(room, event)
+
+    adapter.handle_message.assert_awaited_once()
+    msg = adapter.handle_message.await_args.args[0]
+    assert msg.source.thread_id == "$dm1"
+    assert msg.text == "help me"
+
+
+@pytest.mark.asyncio
+async def test_dm_mention_thread_no_mention_no_thread(monkeypatch):
+    """MATRIX_DM_MENTION_THREADS=true: DM without mention does NOT create a thread."""
+    monkeypatch.setenv("MATRIX_DM_MENTION_THREADS", "true")
+    monkeypatch.setenv("MATRIX_AUTO_THREAD", "false")
+
+    adapter = _make_adapter()
+    room = _make_room(member_count=2)
+    event = _make_event("hello without mention", event_id="$dm1")
+
+    await adapter._on_room_message(room, event)
+    adapter.handle_message.assert_awaited_once()
+    msg = adapter.handle_message.await_args.args[0]
+    assert msg.source.thread_id is None
+
+
+@pytest.mark.asyncio
+async def test_dm_mention_thread_preserves_existing_thread(monkeypatch):
+    """MATRIX_DM_MENTION_THREADS=true: DM already in a thread keeps that thread_id."""
+    monkeypatch.setenv("MATRIX_DM_MENTION_THREADS", "true")
+    monkeypatch.setenv("MATRIX_AUTO_THREAD", "false")
+
+    adapter = _make_adapter()
+    adapter._bot_participated_threads.add("$existing_thread")
+    room = _make_room(member_count=2)
+    event = _make_event("@hermes:example.org help me", thread_id="$existing_thread")
+
+    await adapter._on_room_message(room, event)
+    adapter.handle_message.assert_awaited_once()
+    msg = adapter.handle_message.await_args.args[0]
+    assert msg.source.thread_id == "$existing_thread"
+
+
+@pytest.mark.asyncio
+async def test_dm_mention_thread_tracks_participation(monkeypatch):
+    """DM mention-thread tracks the thread in _bot_participated_threads."""
+    monkeypatch.setenv("MATRIX_DM_MENTION_THREADS", "true")
+    monkeypatch.setenv("MATRIX_AUTO_THREAD", "false")
+
+    adapter = _make_adapter()
+    room = _make_room(member_count=2)
+    event = _make_event("@hermes:example.org help", event_id="$dm1")
+
+    with patch.object(adapter, "_save_participated_threads"):
+        await adapter._on_room_message(room, event)
+
+    assert "$dm1" in adapter._bot_participated_threads
+
+
 # ---------------------------------------------------------------------------
 # YAML config bridge
 # ---------------------------------------------------------------------------
@@ -480,6 +569,25 @@ class TestMatrixConfigBridge:
         assert os.getenv("MATRIX_FREE_RESPONSE_ROOMS") == "!room1:example.org,!room2:example.org"
         assert os.getenv("MATRIX_AUTO_THREAD") == "false"
 
+    def test_yaml_bridge_sets_dm_mention_threads(self, monkeypatch, tmp_path):
+        """Matrix YAML dm_mention_threads should bridge to env var."""
+        monkeypatch.delenv("MATRIX_DM_MENTION_THREADS", raising=False)
+
+        import os
+        import yaml
+
+        yaml_content = {"matrix": {"dm_mention_threads": True}}
+        config_file = tmp_path / "config.yaml"
+        config_file.write_text(yaml.dump(yaml_content))
+
+        yaml_cfg = yaml.safe_load(config_file.read_text())
+        matrix_cfg = yaml_cfg.get("matrix", {})
+        if isinstance(matrix_cfg, dict):
+            if "dm_mention_threads" in matrix_cfg and not os.getenv("MATRIX_DM_MENTION_THREADS"):
+                monkeypatch.setenv("MATRIX_DM_MENTION_THREADS", str(matrix_cfg["dm_mention_threads"]).lower())
+
+        assert os.getenv("MATRIX_DM_MENTION_THREADS") == "true"
+
     def test_env_vars_take_precedence_over_yaml(self, monkeypatch):
         """Env vars should not be overwritten by YAML values."""
         monkeypatch.setenv("MATRIX_REQUIRE_MENTION", "true")

website/docs/reference/environment-variables.md

@@ -262,6 +262,7 @@ For cloud sandbox backends, persistence is filesystem-oriented. `TERMINAL_LIFETI
 | `MATRIX_REQUIRE_MENTION` | Require `@mention` in rooms (default: `true`). Set to `false` to respond to all messages. |
 | `MATRIX_FREE_RESPONSE_ROOMS` | Comma-separated room IDs where bot responds without `@mention` |
 | `MATRIX_AUTO_THREAD` | Auto-create threads for room messages (default: `true`) |
+| `MATRIX_DM_MENTION_THREADS` | Create a thread when bot is `@mentioned` in a DM (default: `false`) |
 | `HASS_TOKEN` | Home Assistant Long-Lived Access Token (enables HA platform + tools) |
 | `HASS_URL` | Home Assistant URL (default: `http://homeassistant.local:8123`) |
 | `WEBHOOK_ENABLED` | Enable the webhook platform adapter (`true`/`false`) |

website/docs/user-guide/messaging/matrix.md

@@ -16,7 +16,7 @@ Before setup, here's the part most people want to know: how Hermes behaves once
 
 | Context | Behavior |
 |---------|----------|
-| **DMs** | Hermes responds to every message. No `@mention` needed. Each DM has its own session. |
+| **DMs** | Hermes responds to every message. No `@mention` needed. Each DM has its own session. Set `MATRIX_DM_MENTION_THREADS=true` to start a thread when the bot is `@mentioned` in a DM. |
 | **Rooms** | By default, Hermes requires an `@mention` to respond. Set `MATRIX_REQUIRE_MENTION=false` or add room IDs to `MATRIX_FREE_RESPONSE_ROOMS` for free-response rooms. Room invites are auto-accepted. |
 | **Threads** | Hermes supports Matrix threads (MSC3440). If you reply in a thread, Hermes keeps the thread context isolated from the main room timeline. Threads where the bot has already participated do not require a mention. |
 | **Auto-threading** | By default, Hermes auto-creates a thread for each message it responds to in a room. This keeps conversations isolated. Set `MATRIX_AUTO_THREAD=false` to disable. |
@@ -62,6 +62,7 @@ matrix:
   free_response_rooms:            # Rooms exempt from mention requirement
     - "!abc123:matrix.org"
   auto_thread: true               # Auto-create threads for responses (default: true)
+  dm_mention_threads: false       # Create thread when @mentioned in DM (default: false)
 ```
 
 Or via environment variables:
@@ -70,6 +71,7 @@ Or via environment variables:
 MATRIX_REQUIRE_MENTION=true
 MATRIX_FREE_RESPONSE_ROOMS=!abc123:matrix.org,!def456:matrix.org
 MATRIX_AUTO_THREAD=true
+MATRIX_DM_MENTION_THREADS=false
 ```
 
 :::note