diagnose

name	diagnose
description	Disciplined diagnosis loop for a hard bug or performance regression — reproduce → minimize → hypothesize → instrument → fix the cause → regression-test. Use when something is broken / throwing / failing or regressed, or when the user says "diagnose this", "debug this", "버그 진단", "왜 안 되지", "디버깅".
argument-hint	[the symptom]
allowed-tools	Read, Grep, Glob, Bash, Edit, Write

diagnose

Don't guess-and-patch. Find the real cause, then fix it.

Loop

1. Reproduce — get a reliable, minimal repro. A bug you can't reproduce, you can't confirm you fixed. Capture the exact failing command + output.
2. Minimize — strip the repro to the smallest input / path that still fails. The minimal case usually names the cause.
3. Hypothesize — state ONE falsifiable hypothesis ("X is null because Y returns early when Z"), not a vibe — a claim a check can disprove.
4. Instrument — add the cheapest probe (a log, an assert, a breakpoint) that confirms or kills the hypothesis. Let evidence decide, not intuition. Killed → back to step 3.
5. Fix the cause, not the symptom. A narrow patch that hides the symptom while the cause remains is a stopgap — label it as one if you must ship it.
6. Regression-test — write a test that fails before the fix and passes after, so the bug can't silently return.

Discipline

• Verify against the REAL system (a real query / real run), never inferred from code alone.
• One hypothesis at a time; record what you ruled out.
• "Looks fixed" is not fixed — the regression test (red → green) is the proof.