Apply attempts so far; at the configured cap the worker dead-letters the row.
The provider's event id: the dedupe key on enqueue and the submitted operation's idempotencyKey, so a redelivered event resolves to the same money move at most once.
Why the worker gave up, set when the row goes 'dead'; null otherwise.
When the verified event was enqueued.
'pending' is the only status claimInbound ever hands back; 'applied' and 'dead' are terminal.
One stored inbox row: a verified inbound event mapped to the operation it applies (see InboxStore).