Add a new config option group_user_isolation (default: false) to the
DingTalk channel. When enabled, each user in a group chat gets their own
session while bot replies are still routed to the shared group chat.
Audited all channel implementations for overly broad exception handling
that causes retry amplification or silent message loss during network
errors. This is the same class of bug as #3050 (Telegram _send_text).
Fixes by channel:
Telegram (send_delta):
- _stream_end path used except Exception for HTML edit fallback
- Network errors (TimedOut, NetworkError) triggered redundant plain
text edit, doubling connection demand during pool exhaustion
- Changed to except BadRequest, matching the _send_text fix
Discord:
- send() caught all exceptions without re-raising
- ChannelManager._send_with_retry() saw successful return, never retried
- Messages silently dropped on any send failure
- Added raise after error logging
DingTalk:
- _send_batch_message() returned False on all exceptions including
network errors — no retry, fallback text sent unnecessarily
- _read_media_bytes() and _upload_media() swallowed transport errors,
causing _send_media_ref() to cascade through doomed fallback attempts
- Added except httpx.TransportError handlers that re-raise immediately
WeChat:
- Media send failure triggered text fallback even for network errors
- During network issues: 3×(media + text) = 6 API calls per message
- Added specific catches: TimeoutException/TransportError re-raise,
5xx HTTPStatusError re-raises, 4xx falls back to text
QQ:
- _send_media() returned False on all exceptions
- Network errors triggered fallback text instead of retry
- Added except (aiohttp.ClientError, OSError) that re-raises
Tests: 331 passed (283 existing + 48 new across 5 channel test files)
Fixes: #3054
Related: #3050, #3053
