Daoyuan Li 9a4c72db99
fix(channels): isolate per-message failures in WeChat poll loop (#4231)
_poll_loop persisted the long-poll cursor (get_updates_buf) for the whole
getupdates batch immediately on receipt, then iterated data["msgs"] with no
per-message error handling. If any single message's processing raised (e.g.
an attachment that fails to decrypt), the for loop aborted and every message
after the failing one in that batch was never handled -- but since the cursor
had already advanced past the whole batch, the next poll would never re-fetch
them. The loss was silent and permanent, not a delay.

Fix is two parts:
- Wrap each _handle_update call in its own try/except (re-raising
  CancelledError) so one bad message is logged and skipped instead of
  aborting the rest of the batch.
- Move the cursor advance/persist to after the per-message loop instead of
  before it, so a hard crash mid-batch leaves the cursor unmoved. Worst case
  becomes re-fetching and re-processing the batch on restart, not silently
  skipping messages that were never actually handled.

Regression test drives the real _handle_update over a 3-message batch where
the middle message is a WeChat image item with deliberately non-block-aligned
"encrypted" bytes, so decryption raises a genuine cryptography ValueError
(the same failure shape a corrupt real attachment would produce). Confirms
the first and third messages both still reach the bus, the failure is logged
with the message id, and the persisted cursor reflects the fully-attempted
batch.
2026-07-17 16:08:53 +08:00
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