phx:learn-from-fix

Learn From Fix

After fixing a bug or receiving a correction, capture the lesson to prevent future mistakes.

Usage

/phx:learn-from-fix Fixed N+1 query in user listing - was missing preload
/phx:learn-from-fix String vs atom key mismatch in params handling
/phx:learn-from-fix LiveView assign_async needs render_async in tests

Workflow

Step 1: Identify the Pattern

Look at recent conversation context. Ask yourself:

• What was the root cause? (not the symptom)
• Is this a common mistake others might make?
• Can it be prevented with a simple rule?

Step 2: Check Existing Knowledge

Check if already documented:

• Grep project CLAUDE.md for the pattern keyword
• Check auto-memory files for similar lessons
• Read ${CLAUDE_SKILL_DIR}/references/common-mistakes.md (READ-ONLY plugin reference — do NOT edit this file)

If already documented, tell the user and stop.

Step 3: Decide Where to Save

CRITICAL: NEVER edit plugin files. Files under ~/.claude/plugins/ are cached and get overwritten on updates. Always write to project or memory locations.

Scope	Write to	Example
This project only	Project CLAUDE.md	"Never use raw SQL in this app"
All Elixir projects	Auto-memory MEMORY.md	"jsonb always uses string keys"
Detailed fix with context	.claude/solutions/ via /phx:compound	Complex debugging story

Step 4: Write the Lesson

For project CLAUDE.md — append a concise rule:

### [Category] Iron Laws (continued)

N. **[SHORT RULE NAME]** — Do NOT [bad pattern]. Instead [good pattern]

For auto-memory — append to ~/.claude/projects/{project-hash}/memory/MEMORY.md:

### Lesson: [Title]
- **Pattern**: Do NOT [bad] — instead [good]
- **Why**: [root cause explanation]

Step 5: Consider Broader Updates

If the lesson is significant enough to be an Iron Law:

• Suggest adding to project CLAUDE.md Iron Laws section
• If it's universal (applies to all Elixir projects), suggest updating the plugin itself (the user can PR it)

Output

After capturing, confirm:

Lesson captured in [location]

Pattern: Do NOT [bad pattern] — instead [good pattern]
Category: [Ecto/LiveView/OTP/Testing/etc]

Iron Laws

1. NEVER edit plugin files — files under ~/.claude/plugins/ are cached and overwritten on updates
2. DO NOT duplicate existing lessons — always check CLAUDE.md and memory before writing
3. Capture the root cause, not the symptom — "missing preload" not "query was slow"

References (READ-ONLY — do NOT edit)

• ${CLAUDE_SKILL_DIR}/references/common-mistakes.md — Common Elixir mistakes reference. Consult when checking for duplicates. Ships with the plugin — NEVER modify.