git-bisect

Goal: pinpoint the exact commit that caused a regression. Use for: - a bug that appeared somewhere in a range of commits - regressions with a clear good and bad state - narrowing blame when the diff is large Workflow: 1. Find a known-good and a known-bad commit. 2. Start bisect: mark bad, then mark good. 3. Test the checkout git selects at each step. 4. Mark each as good or bad to halve the range. 5. Let bisect converge on the first bad commit. 6. Reset bisect and inspect that commit's diff. Automate: - write a script that exits 0 (good) or non-zero (bad) - run git bisect run <script> to search hands-free - ensure the test reliably reproduces the bug Rules: - use a reliable, fast reproducer for each step - keep the working tree clean between steps - run git bisect reset when finished - a flaky test makes bisect lie; stabilize it first