Systematic debugging

Iron law

No fixes without a reproduced failure and a testable hypothesis. After three failed fix attempts, question architecture or assumptions.

When to use

• Intermittent or unclear failures
• Prior "quick fixes" did not hold
• Multiple subsystems involved (API, DB, cache, agent tools)

When not to use

• Typo or one-line obvious fix with clear error message
• User only wants a stack trace explained, not a fix

Four phases