Obsidian Foundry: Self-Verifying Dark Factory

Obsidian Foundry is a four-seat software factory in Band Desktop. We gave it one message, the pocketful task, and stepped away. It built all four stages of a wallet and payments service where money must never be created, destroyed or spent twice, under concurrent transfers, retries and rounding. The seats: a coordinator turns the spec into a numbered requirement ledger and hands out work, but never writes code. An implementer writes the Go service. A tester writes a black-box acceptance suite from the ledger alone, without reading the product code, so it can't share the implementer's blind spots. A reviewer builds from a clean checkout with no network, runs the shipped checks and the tester's suite, checks that every requirement is covered, reads the code, then accepts or rejects one exact commit. Why this design: the shipped checks cover 79% of stage 1 but only 9% of stage 3. A factory that stops when the checks turn green stops right where the hidden tests begin. Our ledger marks the edge cases the shipped checks are least likely to probe, and the tester goes after them. Results: 260 requirements, 4,090 lines of Go, 242 API tests and 58 browser tests. All four folders claim their stage in isolated mode (no network, 2 vCPU, 2 GiB). Two rejections each changed the work. The best one: in stage 4, every shipped check and the tester's suite passed, but code review found that batch-correction precedence depended on item order. The fix shipped with a new test for every order. Cost: 113M tokens, about $49 at list prices, roughly $12 per stage. The mandates are generic, so you can point the same factory at a different problem by changing one task file.