The active poll (1s, running sessions) and sweep poll (60s, all active
sessions) both call deliverSessionMessages, and a running session is in
both result sets. Without locking they race on the same outbound row:
both read it as undelivered, both call the channel adapter, both
markDelivered. INSERT OR IGNORE hides the DB collision but the user has
already received the message twice.
Adds a per-session inflight guard; the second concurrent caller skips
and picks up any leftover work on the next poll tick.
Also makes outbox cleanup in deliverMessage best-effort: the message is
already on the user's screen, so a cleanup throw must not propagate to
the retry path (which would resend).
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
