ask-bug-finder（询问错误查找器）

<critical_constraints> ❌ NO fixing without reproducing first ❌ NO changing random things hoping it works ❌ NO fixing symptoms instead of root cause ✅ MUST read full error message including stack trace ✅ MUST form hypothesis before making changes ✅ MUST write test after fixing to prevent recurrence </critical_constraints>

<common_patterns>

• Off-by-one: range(len(x)-1) → should be range(len(x))
• Null reference: user.name without checking user is None
• Race condition: check-then-act pattern
• State mutation: items.sort() modifies original </common_patterns>

<when_stuck>

1. Take a break
2. Explain to someone (rubber duck)
3. Check the obvious (is server running?)
4. Search for similar issues
5. Create minimal reproduction </when_stuck>