---
name: principle-fix-root-causes
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."
disable-model-invocation: true
---

# Fix Root Causes

When debugging, do not fix symptoms. Trace every problem to its root cause and fix it there.

**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.

**Pattern:**
- Reproduce first
- Ask "why" until you hit the root cause
- Do not add guards (adding a nil check to silence a crash is a symptom fix)
- If a workaround needs a paragraph-long comment to justify it, the code is wrong (fix the code, not the comment)
- Check for the pattern, not just the instance (grep for the same pattern, fix all instances)
- When stuck, instrument. Don't guess (add logging, read the actual error)

**Restart bugs: suspect state before code**

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.

## Session capabilities and permissions

Use the exposed tools and observed operations described in [host capabilities](../../references/host-capabilities.md). Reproduce, instrument and fix only within the user's authorized scope and host permissions. Clearing or changing persistent state also requires authorization. If reproduction, inspection or writes are unavailable or denied, state the missing capability and give the remaining investigation steps. Keep unobserved causes and fixes unverified.