Diagnosing Bugs

Use this loop for uncertain or hard-to-reproduce bugs and performance regressions. Scale the investigation to the uncertainty. When a trace, failing test, or direct code evidence already establishes the cause, apply the authorized narrow fix and verify the original symptom; do not manufacture extra hypotheses or minimise a repro that already isolates the fault.

When exploring the codebase, read CONTEXT.md (if it exists) to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.

Phase 1 — Build a feedback loop

This is the skill. Everything else is mechanical. If you have a tight pass/fail signal for the bug — one that goes red on this bug — you will find the cause; bisection, hypothesis-testing, and instrumentation all just consume it. If you don't have one, no amount of staring at code will save you.

Invest enough to distinguish the reported failure from nearby symptoms. Timebox unsuccessful approaches; switch methods or identify missing evidence rather than repeating unproductive attempts.

Ways to construct one — choose the smallest suitable method