debugging-and-error-recovery

Reproduce the failure reliably first, then localize which layer is failing, reduce to a minimal failing case, and fix the root cause rather than the symptom. Finish by adding a regression test that fails without the fix and verifying the full suite passes.

Run git bisect start, mark the current commit bad and a known working commit good, then test each midpoint checkout. You can automate it with git bisect run followed by your focused test command to identify the exact breaking commit.

Classify it as timing-dependent, environment-dependent, state-dependent, or truly random. Add timestamps or artificial delays for race conditions, compare environments and data states, run scenarios in isolation, and add defensive logging with alerts for recurring signatures.

Symptom fixes mask the underlying defect, so the bug resurfaces elsewhere and compounds with later changes. Asking why the failure happens until reaching the actual cause, such as fixing a duplicating JOIN query rather than deduplicating in the UI, prevents recurrence.

Remove instrumentation once the bug is fixed and a regression test guards against recurrence, or when logs are only useful during development. Always remove logs containing sensitive data, but keep permanent error boundaries and API error logging with request context.