Follow-ups to the salvaged #80032 fatal-error escalation, closing the
gaps its review thread identified plus a sibling of the same class:
1. Partial-batch loss: _check_inbox now dispatches whatever the fetch
returned BEFORE escalating a failure — the early-return dropped
already-fetched messages whose UIDs were marked seen.
2. Seen-after-fetch: UIDs enter _seen_uids only after their fetch
returns a response, so a mid-batch connection failure leaves the
remaining UIDs eligible for the next poll. Per-message processing
moved to _parse_fetched_message behind a poison guard: a message
that fails parsing/auth-verification is marked seen, logged with
its UID, and skipped once — never an eternal crash loop.
3. Reconnect mail loss: connect(is_reconnect=True) restores the
account's seen-UID baseline from a class-level snapshot instead of
re-marking the entire mailbox seen — mail that arrived during an
outage is now processed after the reconnect the escalation triggers.
7 new regression tests.
a7f0abc845