feat(mattermost): configurable mention behavior — respond without @mention

Adds MATTERMOST_REQUIRE_MENTION and MATTERMOST_FREE_RESPONSE_CHANNELS
env vars, matching Discord's existing mention gating pattern.

- MATTERMOST_REQUIRE_MENTION=false: respond to all channel messages
- MATTERMOST_FREE_RESPONSE_CHANNELS=id1,id2: specific channels where
  bot responds without @mention even when require_mention is true
- DMs always respond regardless of mention settings
- @mention is now stripped from message text (clean agent input)

7 new tests for mention gating, free-response channels, DM bypass,
and mention stripping. Updated existing test for mention stripping.

Docs: updated mattermost.md with Mention Behavior section,
environment-variables.md with new vars, config.py with metadata.

gateway/platforms/mattermost.py

@@ -603,9 +603,19 @@ class MattermostAdapter(BasePlatformAdapter):
         # For DMs, user_id is sufficient.  For channels, check for @mention.
         message_text = post.get("message", "")
 
-        # Mention-only mode: skip channel messages that don't @mention the bot.
+        # Mention-gating for non-DM channels.
-        # DMs (type "D") are always processed.
+        # Config (env vars):
+        #   MATTERMOST_REQUIRE_MENTION: Require @mention in channels (default: true)
+        #   MATTERMOST_FREE_RESPONSE_CHANNELS: Channel IDs where bot responds without mention
         if channel_type_raw != "D":
+            require_mention = os.getenv(
+                "MATTERMOST_REQUIRE_MENTION", "true"
+            ).lower() not in ("false", "0", "no")
+
+            free_channels_raw = os.getenv("MATTERMOST_FREE_RESPONSE_CHANNELS", "")
+            free_channels = {ch.strip() for ch in free_channels_raw.split(",") if ch.strip()}
+            is_free_channel = channel_id in free_channels
+
             mention_patterns = [
                 f"@{self._bot_username}",
                 f"@{self._bot_user_id}",
@@ -614,13 +624,21 @@ class MattermostAdapter(BasePlatformAdapter):
                 pattern.lower() in message_text.lower()
                 for pattern in mention_patterns
             )
-            if not has_mention:
+
+            if require_mention and not is_free_channel and not has_mention:
                 logger.debug(
                     "Mattermost: skipping non-DM message without @mention (channel=%s)",
                     channel_id,
                 )
                 return
 
+            # Strip @mention from the message text so the agent sees clean input.
+            if has_mention:
+                for pattern in mention_patterns:
+                    message_text = re.sub(
+                        re.escape(pattern), "", message_text, flags=re.IGNORECASE
+                    ).strip()
+
         # Resolve sender info.
         sender_id = post.get("user_id", "")
         sender_name = data.get("sender_name", "").lstrip("@") or sender_id

hermes_cli/config.py

@@ -817,6 +817,20 @@ OPTIONAL_ENV_VARS = {
         "password": False,
         "category": "messaging",
     },
+    "MATTERMOST_REQUIRE_MENTION": {
+        "description": "Require @mention in Mattermost channels (default: true). Set to false to respond to all messages.",
+        "prompt": "Require @mention in channels",
+        "url": None,
+        "password": False,
+        "category": "messaging",
+    },
+    "MATTERMOST_FREE_RESPONSE_CHANNELS": {
+        "description": "Comma-separated Mattermost channel IDs where bot responds without @mention",
+        "prompt": "Free-response channel IDs (comma-separated)",
+        "url": None,
+        "password": False,
+        "category": "messaging",
+    },
     "MATRIX_HOMESERVER": {
         "description": "Matrix homeserver URL (e.g. https://matrix.example.org)",
         "prompt": "Matrix homeserver URL",

tests/gateway/test_mattermost.py

@@ -1,5 +1,6 @@
 """Tests for Mattermost platform adapter."""
 import json
+import os
 import time
 import pytest
 from unittest.mock import MagicMock, patch, AsyncMock
@@ -269,6 +270,7 @@ class TestMattermostWebSocketParsing:
     def setup_method(self):
         self.adapter = _make_adapter()
         self.adapter._bot_user_id = "bot_user_id"
+        self.adapter._bot_username = "hermes-bot"
         # Mock handle_message to capture the MessageEvent without processing
         self.adapter.handle_message = AsyncMock()
 
@@ -293,7 +295,8 @@ class TestMattermostWebSocketParsing:
         await self.adapter._handle_ws_event(event)
         assert self.adapter.handle_message.called
         msg_event = self.adapter.handle_message.call_args[0][0]
-        assert msg_event.text == "@bot_user_id Hello from Matrix!"
+        # @mention is stripped from the message text
+        assert msg_event.text == "Hello from Matrix!"
         assert msg_event.message_id == "post_abc"
 
     @pytest.mark.asyncio
@@ -410,6 +413,87 @@ class TestMattermostWebSocketParsing:
         assert not self.adapter.handle_message.called
 
 
+# ---------------------------------------------------------------------------
+# Mention behavior (require_mention + free_response_channels)
+# ---------------------------------------------------------------------------
+
+class TestMattermostMentionBehavior:
+    def setup_method(self):
+        self.adapter = _make_adapter()
+        self.adapter._bot_user_id = "bot_user_id"
+        self.adapter._bot_username = "hermes-bot"
+        self.adapter.handle_message = AsyncMock()
+
+    def _make_event(self, message, channel_type="O", channel_id="chan_456"):
+        post_data = {
+            "id": "post_mention",
+            "user_id": "user_123",
+            "channel_id": channel_id,
+            "message": message,
+        }
+        return {
+            "event": "posted",
+            "data": {
+                "post": json.dumps(post_data),
+                "channel_type": channel_type,
+                "sender_name": "@alice",
+            },
+        }
+
+    @pytest.mark.asyncio
+    async def test_require_mention_true_skips_without_mention(self):
+        """Default: messages without @mention in channels are skipped."""
+        with patch.dict(os.environ, {}, clear=False):
+            os.environ.pop("MATTERMOST_REQUIRE_MENTION", None)
+            os.environ.pop("MATTERMOST_FREE_RESPONSE_CHANNELS", None)
+            await self.adapter._handle_ws_event(self._make_event("hello"))
+            assert not self.adapter.handle_message.called
+
+    @pytest.mark.asyncio
+    async def test_require_mention_false_responds_to_all(self):
+        """MATTERMOST_REQUIRE_MENTION=false: respond to all channel messages."""
+        with patch.dict(os.environ, {"MATTERMOST_REQUIRE_MENTION": "false"}):
+            await self.adapter._handle_ws_event(self._make_event("hello"))
+            assert self.adapter.handle_message.called
+
+    @pytest.mark.asyncio
+    async def test_free_response_channel_responds_without_mention(self):
+        """Messages in free-response channels don't need @mention."""
+        with patch.dict(os.environ, {"MATTERMOST_FREE_RESPONSE_CHANNELS": "chan_456,chan_789"}):
+            os.environ.pop("MATTERMOST_REQUIRE_MENTION", None)
+            await self.adapter._handle_ws_event(self._make_event("hello", channel_id="chan_456"))
+            assert self.adapter.handle_message.called
+
+    @pytest.mark.asyncio
+    async def test_non_free_channel_still_requires_mention(self):
+        """Channels NOT in free-response list still require @mention."""
+        with patch.dict(os.environ, {"MATTERMOST_FREE_RESPONSE_CHANNELS": "chan_789"}):
+            os.environ.pop("MATTERMOST_REQUIRE_MENTION", None)
+            await self.adapter._handle_ws_event(self._make_event("hello", channel_id="chan_456"))
+            assert not self.adapter.handle_message.called
+
+    @pytest.mark.asyncio
+    async def test_dm_always_responds(self):
+        """DMs (channel_type=D) always respond regardless of mention settings."""
+        with patch.dict(os.environ, {}, clear=False):
+            os.environ.pop("MATTERMOST_REQUIRE_MENTION", None)
+            await self.adapter._handle_ws_event(self._make_event("hello", channel_type="D"))
+            assert self.adapter.handle_message.called
+
+    @pytest.mark.asyncio
+    async def test_mention_stripped_from_text(self):
+        """@mention is stripped from message text."""
+        with patch.dict(os.environ, {}, clear=False):
+            os.environ.pop("MATTERMOST_REQUIRE_MENTION", None)
+            await self.adapter._handle_ws_event(
+                self._make_event("@hermes-bot what is 2+2")
+            )
+            assert self.adapter.handle_message.called
+            msg = self.adapter.handle_message.call_args[0][0]
+            assert "@hermes-bot" not in msg.text
+            assert "2+2" in msg.text
+
+
 # ---------------------------------------------------------------------------
 # File upload (send_image)
 # ---------------------------------------------------------------------------

website/docs/reference/environment-variables.md

@@ -200,6 +200,8 @@ For native Anthropic auth, Hermes prefers Claude Code's own credential files whe
 | `MATTERMOST_TOKEN` | Bot token or personal access token for Mattermost |
 | `MATTERMOST_ALLOWED_USERS` | Comma-separated Mattermost user IDs allowed to message the bot |
 | `MATTERMOST_HOME_CHANNEL` | Channel ID for proactive message delivery (cron, notifications) |
+| `MATTERMOST_REQUIRE_MENTION` | Require `@mention` in channels (default: `true`). Set to `false` to respond to all messages. |
+| `MATTERMOST_FREE_RESPONSE_CHANNELS` | Comma-separated channel IDs where bot responds without `@mention` |
 | `MATTERMOST_REPLY_MODE` | Reply style: `thread` (threaded replies) or `off` (flat messages, default) |
 | `MATRIX_HOMESERVER` | Matrix homeserver URL (e.g. `https://matrix.org`) |
 | `MATRIX_ACCESS_TOKEN` | Matrix access token for bot authentication |

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

@@ -149,6 +149,12 @@ MATTERMOST_ALLOWED_USERS=3uo8dkh1p7g1mfk49ear5fzs5c
 
 # Optional: reply mode (thread or off, default: off)
 # MATTERMOST_REPLY_MODE=thread
+
+# Optional: respond without @mention (default: true = require mention)
+# MATTERMOST_REQUIRE_MENTION=false
+
+# Optional: channels where bot responds without @mention (comma-separated channel IDs)
+# MATTERMOST_FREE_RESPONSE_CHANNELS=channel_id_1,channel_id_2
 ```
 
 Optional behavior settings in `~/.hermes/config.yaml`:
@@ -206,6 +212,19 @@ Set it in your `~/.hermes/.env`:
 MATTERMOST_REPLY_MODE=thread
 ```
 
+## Mention Behavior
+
+By default, the bot only responds in channels when `@mentioned`. You can change this:
+
+| Variable | Default | Description |
+|----------|---------|-------------|
+| `MATTERMOST_REQUIRE_MENTION` | `true` | Set to `false` to respond to all messages in channels (DMs always work). |
+| `MATTERMOST_FREE_RESPONSE_CHANNELS` | _(none)_ | Comma-separated channel IDs where the bot responds without `@mention`, even when require_mention is true. |
+
+To find a channel ID in Mattermost: open the channel, click the channel name header, and look for the ID in the URL or channel details.
+
+When the bot is `@mentioned`, the mention is automatically stripped from the message before processing.
+
 ## Troubleshooting
 
 ### Bot is not responding to messages