Observability hook (which adapter matched, verification failures, ...).
Exceptions it throws are swallowed — logging never changes the handler's
result.
Receives the normalized event. Must be fast (enqueue, don't process).
Dedupe by event.id is the HOST's responsibility — PayFanout stores nothing.
A thrown error yields a 500 so the PSP retries delivery.
Observability hook (which adapter matched, verification failures, ...). Exceptions it throws are swallowed — logging never changes the handler's result.