fix(channels): accept leading @mentions before /connect bind codes (#4222)

* fix(channels): accept leading @mentions before /connect bind codes

Group chats often deliver "@bot /connect <code>" (Feishu/DingTalk leave the
mention in the text). extract_connect_code required the message to start with
/connect, so those binds silently failed while Slack/Discord already strip
mentions before parsing. Skip leading mention tokens in the shared helper.

* test(channels): pin mention variants and case-insensitive /connect parsing

backend/app/channels/commands.py

@@ -21,14 +21,42 @@ KNOWN_CHANNEL_COMMANDS: frozenset[str] = frozenset(
 )
 
 
+def _is_leading_mention_token(token: str) -> bool:
+    """Return whether *token* looks like a platform bot/user mention.
+
+    Group chats often require ``@bot`` before the message is delivered. Slack
+    and Discord strip those tokens before connect parsing; Feishu / DingTalk
+    leave them in the text (``@_user_1``, ``@bot``, ``<@id>``). Treat them as
+    transport noise only when they lead the message so
+    ``@bot /connect <code>`` still binds.
+    """
+    if not token:
+        return False
+    # Slack / Discord style: <@U123> or <@!U123> or <@U123|name>
+    if token.startswith("<@") and token.endswith(">"):
+        return True
+    # Feishu / DingTalk / generic: @_user_1, @bot, @nickname
+    if token.startswith("@") and len(token) > 1:
+        return True
+    return False
+
+
 def extract_connect_code(text: str) -> str | None:
-    """Extract the one-time channel binding code from a connect command."""
+    """Extract the one-time channel binding code from a connect command.
+
+    Accepts a leading platform mention so group ``@bot /connect <code>``
+    messages bind the same way as bare ``/connect <code>`` (Slack/Discord
+    already strip mentions before calling this helper).
+    """
     parts = text.strip().split()
-    if len(parts) < 2:
+    index = 0
+    while index < len(parts) and _is_leading_mention_token(parts[index]):
+        index += 1
+    if index + 1 >= len(parts):
         return None
-    command = parts[0].lower()
+    command = parts[index].lower()
     if command in {"/connect", "connect"}:
-        return parts[1]
+        return parts[index + 1]
     return None
 
 

backend/tests/test_additional_channel_connections.py

@@ -6,6 +6,7 @@ from datetime import UTC, datetime, timedelta
 from unittest.mock import AsyncMock, MagicMock
 
 from app.channels.base import Channel
+from app.channels.commands import extract_connect_code
 from app.channels.message_bus import InboundMessage, MessageBus, OutboundMessage
 
 
@@ -29,11 +30,42 @@ def test_pending_connect_code_extracts_code_when_connections_configured():
     assert channel._pending_connect_code("hello world") is None
 
 
+def test_pending_connect_code_accepts_leading_platform_mentions():
+    """Group chats prefix @bot; Feishu/DingTalk leave that noise in the text.
+
+    Slack/Discord strip mentions before this helper; the shared parser must
+    still accept the unstripped form so @bot /connect <code> binds.
+    """
+    assert extract_connect_code("@_user_1 /connect abc123") == "abc123"
+    assert extract_connect_code("@bot  /connect code-xyz") == "code-xyz"
+    assert extract_connect_code("@bot @_user_2 /connect multi") == "multi"
+    # All three Slack/Discord mention forms the _is_leading_mention_token
+    # docstring enumerates: plain, ping (<@!id>), and name (<@id|name>).
+    assert extract_connect_code("<@U123ABC> /connect slackish") == "slackish"
+    assert extract_connect_code("<@!U123ABC> /connect pinged") == "pinged"
+    assert extract_connect_code("<@U123ABC|alice> /connect named") == "named"
+    # Command match is case-insensitive after the mention prefix.
+    assert extract_connect_code("@bot /Connect cased") == "cased"
+    # Mentions without a connect command stay non-binding.
+    assert extract_connect_code("@_user_1 hello") is None
+    # Mention-only / empty input yields no code (boundary guard).
+    assert extract_connect_code("@bot") is None
+    assert extract_connect_code("") is None
+    # Connect not at the command position after mentions does not bind.
+    assert extract_connect_code("please @bot /connect leaked") is None
+    # Mid-sentence /connect must not bind (unchanged).
+    assert extract_connect_code("hi /connect abc123") is None
+
+    channel = _StubChannel(name="stub", bus=MessageBus(), config={"connection_repo": object()})
+    assert channel._pending_connect_code("@_user_1 /connect via-base") == "via-base"
+
+
 def test_pending_connect_code_is_none_when_connections_disabled():
     # With no connection repo, binding is not configured and connect codes are
     # ignored so the message falls through to normal handling.
     channel = _StubChannel(name="stub", bus=MessageBus(), config={})
     assert channel._pending_connect_code("/connect abc123") is None
+    assert channel._pending_connect_code("@bot /connect abc123") is None
 
 
 async def _make_repo(tmp_path, name: str):