Enqueue the calculation onto the worker queue — subject to coverage.

Idempotent: a row in a non-terminal state (queued/running/polling) is not re-enqueued; a row in succeeded is returned untouched — a finished result is a record of one run, so re-pricing the part after its inputs changed (inputs_changed_since_run) means creating a new calculation on the same revision and running that; a row in failed/cancelled/timed_out is reset to queued and re-enqueued so the user can retry.

Coverage: before enqueueing, the org's included-calculation quota is checked. A hard-capped org with no included extraction left FAILS FAST: the calc is parked as blocked (never a queued orphan) and the request raises 402 quota_exceeded with the upgrade path (F-2) — except when the dedup cache can serve an identical prior run, which stays free even over quota. A payment-blocked (dunning) org or an over-spend-cap API key still parks with a coverage payload on a 2xx. A blocked row resumes through this same path once unblocked, without spending a retry attempt.