dead_letter triggers have been registerable since v1.1.1 but their
handlers never fired: dispatcher::handle_failure wrote the dead_letters
row and stopped — list_matching_dead_letter had no production caller.
Any deploy v1.1.1–v1.1.6 with dead_letter triggers had silently
non-functional handlers.
The fix: after the dead-letter row is inserted on retry exhaustion, fan
out to matching dead_letter triggers (filtered by source / originating
trigger_id / script_id) and enqueue one outbox row per match carrying a
real-shape TriggerEvent::DeadLetter (the §6 brief field names were stale
— used the actual variant: dead_letter_id, original: Box<TriggerEvent>,
attempts, last_error, trigger_id, script_id, first/last_attempt_at).
The recursion-stop (a handler's own failure isn't re-dead-lettered)
is upheld by the existing is_dead_letter_handler short-circuit.
Tests (DB-gated): handler actually fires with the nested original event;
existing row-create test now also asserts handler-fire; source_filter
excludes non-matching; failing handler does not recurse.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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