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 running the full suite to check for regressions.

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

Determine whether it is timing, environment, or state dependent. Add timestamps and logging around the suspected area, compare environments and data states, try reproducing under load or in CI, and set up alerts for the error signature if it remains intermittent.

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 ensures the fix is durable and the regression test is meaningful.

Add instrumentation when you cannot localize a failure or the issue is intermittent, and remove it once the bug is fixed and guarded by tests. Keep permanent logging only for error boundaries, API error context, and key performance metrics.