The refill can neither double nor be quietly repriced

Every Monday at 09:00, a cron entry in the finance container POSTs /wallet/transfers: amount "25.00", idempotency_key topup-2026-W36, expected_fee_bps 500.

Twenty-five dollars leave General Balance. The platform fee comes off at the transfer: $1.25: and $23.75 lands in AI Balance, the only money the gateway can spend. Server money stays on its own side; the agents cannot reach it.

One Monday the request times out. The script retries. Same key, same amount: the server replays the original receipt with replayed: true and moves nothing. Nobody funds the agents twice.

Months later the fee changes. The script still says 500 basis points, so the transfer is rejected with 409 TRANSFER_FEE_CHANGED. The automation stops until a human re-confirms the new number.

Two balances, one-way transfer between them. The refill can neither double nor be quietly repriced.