A change can look finished on screen while the data behind it was never saved. This is a repeatable procedure that takes one app change from a clear brief to a reproduced defect, a verified repair and a handoff, with the evidence kept beside your project.
It joins planning, debugging and testing around one task-tracker exercise. You get the working fixture, focused instructions, prompts for your agent, and templates for the brief, the bug report and the verification record. The exercise fails on purpose in its broken mode and passes all six acceptance checks in its fixed mode, so you see what a real before and after looks like before you do it on your own app.
The exercise needs Node 20 or later and a browser for user checks. It needs no account, dependency install or network. The planning, debugging, testing and handoff steps it brings together also work on their own.
It does not deploy, prove production security, or verify the truth of a handoff record. The included exercise stores data in the browser, so it does not show account isolation, server persistence or multi-device sync.