# M03-L05 — Challenge: recover known-good work

**Outcome:** Restore intended behavior while retaining useful work and a traceable history.

**Start:** M03-L01–04; supplied history bundle, working toolchain, and preserved practice project.

The challenge combines reproduction, review, and recovery. You receive a prepared fault checkpoint and a useful documentation idea. Your task is to return software to its known-good behavior, preserve the useful note, and produce a short evidence handoff. Do not solve the challenge by deleting the project or replacing shared history without understanding it.

Clone the generic history bundle into a new folder. Create a branch from FAULT-hysteresis, inspect the isolated bad commit, and reproduce its boundary failure. Preserve a useful README clarification in a separate reviewed commit after the recovery so its purpose remains clear. Use the exact fault procedure from Chapter 7; this later checkpoint is a supplied recovery fixture, not a new feature assignment.

Before choosing an operation, distinguish dirty working content, staged content, and committed history. If you have useful uncommitted wording, save it explicitly before a destructive file restore. Revert the isolated fault to retain history, then apply and review the useful README note. Run native tests and the target cross-build from the documented root.

Finish by reproducing the corrected committed source in another checkout where feasible through your private practice remote or a local branch clone. Record which path you used. A same-machine reproduction reuses installed dependencies and does not prove fresh-machine setup. The output remains synthetic/software evidence.

Your handoff should let another session find the current commit, changes made, actual checks, remaining limits, and next action. A claim that tests passed without a command/result record is incomplete. A clean diff achieved by discarding useful work is also incomplete. The success condition includes preservation as well as recovery.

## Practice and completion

Complete the [exercise](exercise.md), then compare your artifact with the separately distributed instructor answer. A lesson acknowledgment records your own progress; it does not certify that a physical test occurred.

## Reading and figures

[Chapter 6](../../../../book/chapters/ch06/chapter.md), [Chapter 7](../../../../book/chapters/ch07/chapter.md). Resources: [Exact recovery sequence](../../../../book/chapters/ch07/resources/recovery-sequence.md). Figure references: SS06-06; SS07-02–06.