A mechanism that works for one product can still hide identity, concurrency, and attribution bugs. This part adds the second instance that forces those assumptions into the open.
Chapters 8 through 12 replace the single-product fixture with a catalog, make stock and reorder policy independent per SKU, trace one signal to one governed need, and make retry converge on one canonical effect. The final chapter assembles release evidence and then demonstrates the limit of that evidence: internal consistency is not the same claim as truth in the world.
By the end, the reader has a pilot-start receipt and a ladder for moving from deterministic local checks toward credentialed evaluation, human review, canary rollout, and wider release. Each rung proves something new; none inherits the claim of the rung above it.
Continue to Chapter 8: The Store becomes a catalog.
