Pay out a receiver's pending withdrawals

Queues paying out every pending withdrawal of receiver on chain_id and answers the job. Poll it with GET /relay/jobs/{chain}/{id}.

One job per receiver drains omni’s get_withdrawals_by_receiver oldest first, one withdrawal at a time: an unpaid one is signed and sent to the chain’s bridge (withdraw) from the relay’s account, which pays the fees; a paid one is cleared on omni (clear_completed_withdrawal). It is done when omni lists none. A signing refusal fails the job with its detail; RPC and node failures are retried with backoff. A withdrawal to the token contract itself or to the zero address is never paid out, nor a Stellar one older than the bridge’s 60-day nonce lifetime (it can only be refunded).

Chains the relay pays out on: EVM chains except Ethereum (1), Base (8453), Linea (59144), Mantle (5000) and Abstract (2741); Gonka (4444119), Stellar (1100) and TON (1117). A chain is also refused (400) while omni’s removal key for it is neither the MPC key nor the one this service holds, since a payout it could not clear would block the receiver’s next withdrawals.

Only a receiver omni holds a withdrawal for is queued: otherwise 404, and nothing is queued. A receiver with a queued or running job answers that job (reused: "active") instead of a new one; within 2 minutes of a job of the receiver that failed, or that already went past the withdrawal asked for (or found nothing), that job is answered too (reused: "cooldown"). A chain’s payout queue holds at most 500 jobs per shard: past it, 429 with Retry-After.