transfer_split sends one on-chain tx to many destinations, so payout rows
in a batch share a tx_hash. The old UNIQUE index on payouts.tx_hash made
the 2nd+ row fail to record, leaving funds sent but rows stranded in
'processing' and re-sendable by the retry service.
- Migration 015 drops the payouts tx_hash unique index (idempotency is
enforced by idx_payouts_one_per_game) and extends that guard to cover
'processing' so no second payable row can be inserted mid-flight.
- Batch completion now updates the whole batch in a single transaction via
id = ANY(...), so rows can't be left half-completed. Per-user stats use
BIGINT arithmetic in SQL (no JS float).
- Ambiguous batch failures are marked 'needs_review' (which the retry
service does NOT pick up) instead of 'failed', preventing a double-send
when transfer_split may have already broadcast. Operator is alerted.
Adds batchPayout.test.js covering the shared-tx_hash completion and the
needs_review failure path. Full suite: 12 suites / 115 tests.
