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
