Update to pstack

{
  "description": "Apply when debugging. Trace each symptom to its root cause and fix it there; reproduce first, ask why until you reach it, resist nil-check guards that silence crashes.",
  "included_files": [],
  "name": "principle-fix-root-causes",
  "skill_md_contents": "---\nname: principle-fix-root-causes\ndescription: \"Apply when debugging. Trace each symptom to its root cause and fix it there; reproduce first, ask why until you reach it, resist nil-check guards that silence crashes.\"\ndisable-model-invocation: true\n---\n\n# Fix Root Causes\n\nWhen debugging, do not paper over symptoms. Trace every problem to its root cause and fix it there.\n\n**Why:** Symptom fixes accumulate. Each workaround makes the system harder to reason about, and the real bug remains. Root-cause fixes are slower upfront but reduce total debugging time.\n\n**Pattern:**\n- Reproduce first (if you can't reproduce it, you can't verify your fix)\n- Ask \"why\" until you hit the root cause\n- Resist the urge to add guards (adding a nil check to silence a crash is a symptom fix)\n- If a workaround needs a paragraph-long comment to justify it, the code is wrong (fix the code, not the comment)\n- Check for the pattern, not just the instance (grep for the same pattern, fix all instances)\n- When stuck, instrument. Don't guess (add logging, read the actual error)\n\n**Restart bugs: suspect state before code**\n\nCode doesn't change between runs. State does. When something \"fails after restart,\" suspect stale persistent state first: config files, caches, lock files, serialized state. If clearing a state file restores behavior, prioritize state validation as the fix.\n"
}