pocketful — a dark-factory build by four agents

pocketful is a wallet-and-payments service — payments by handle, money requests, bill splits, holds with captures and on-the-clock expiry, two-clocks corrections, statements with frozen snapshots, refunds, and operator batch corrections — built end-to-end by a factory of four coding agents in a Band Desktop room, browser product included — login, balances, live feed, mobile-width, assets in-image. The factory: a coordinator splitting each stage into owned work items with self-contained handoffs; two builders in parallel on disjoint files; an independent reviewer (different model) re-running every check before acceptance. The judged run received exactly four human messages — the stage dispatches — and nothing else. The unedited 1,200-message room.json and git history are the evidence; operators never touched stage code. The hard part was money that never lies: the sum of balances always equals the seeded total; no negative balances, even in historical views; a request moves money at most once under any retry storm; amounts are exact integer minor units. These hold by construction — single-writer atomic writes, idempotency keys resolved before validation, batch affordability judged on net effect — and the two clocks make /me?known_at=… honestly report the past while statements freeze into snapshot tokens. Results: all four stages accepted in one dark run; every folder verified in the harness's isolated mode at 100% of its shipped checks (147/147, 35/35, 6/6, 5/5), no overshoot, each accepting the previous stages' exports. The band caught its own bugs pre-acceptance: a nondeterministic ordering tie-break proven fixed with 20 forced trials, a host-mode harness run caught before review, an undefined-vs-null defect found by the reviewer's 92-test suite. Reproduce it: clone the repo, docker build any stage, follow docs/WALKTHROUGH.md's captured use cases. FACTORY.md documents measured cost/time, the failure log, and how to stand the band up on a different problem.