Settle this task's channel with the payer's cumulative voucher

Liquidates a payment channel whose pay.sh session is gone. The payer signs a cumulative voucher with the channel's session key; EM verifies it against the channel's on-chain authorized signer, asks the pay.sh gateway — the channel's fee payer — to broadcast [ed25519, settle, distribute], and then reads the transaction back from the chain to confirm the worker was credited. Neither settle nor distribute takes a signer account, so nobody here gains any authority: without the payer's signature the money cannot move, and with it anyone could submit the same transaction.

EM names the recipients it asks the gateway to pay — the assigned worker's Solana payout address and the platform's worker share in basis points — and the gateway hashes them against the channel's on-chain distributionHash before broadcasting. When any of that is refused, the gateway's own JSON answer travels back NESTED under detail.gateway, uncut, next to the human-readable message.