OptionaldefinitionEntries this drainer dispatched without settling. Either another party
settled the entry first (a lease-expiry takeover, a manual recovery, or a
completion landing while a retry run waited out a backoff), or a retry
run stopped because the claim could no longer be held, which leaves the
entry pending for a later drain. The handler's side effect ran here too:
the at-least-once overlap the EffectHandler contract tells
handlers to tolerate.
The drained instance's pinned definition fingerprint — carried so the drain telemetry event can slice per definition. Absent only for instances pinned before content fingerprinting.