Diagnose Bug

Do not jump from symptom to fix. First establish what is actually happening, whether it is a defect at all, and why.

Gates

These four are the point of the skill; the process below exists to pass them.

1. Reproduce before editing. No product edit until the symptom has been observed through a repeatable signal. If it cannot be reproduced, say what was tried and what is needed — do not fix by guess.
2. Hypothesis before change. Each candidate cause is stated as a falsifiable prediction and tested before any fix is written.
3. Verify with the same signal. A fix is confirmed by rerunning the reproduction and seeing the symptom gone. Apply /verification-evidence.
4. Stay on this bug. Other problems found along the way are reported, not fixed in the same change.

Process

1. Restate the Symptom

Capture the report in concrete terms: what happened, what was expected, where, and the inputs, environment, timing, or recent changes known. Separate observed facts from guesses. A pasted error or log with no request attached is still a report; restate what it shows.