elixir-phoenix-learn-from-fix

name	elixir-phoenix-learn-from-fix
description	Capture durable lessons after a Phoenix bug fix or correction.
metadata	{"short-description":"Capture lessons from Phoenix fixes"}

Learn From Fix

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

Usage

`elixir-phoenix-learn-from-fix` Fixed N+1 query in user listing - was missing preload
`elixir-phoenix-learn-from-fix` String vs atom key mismatch in params handling
`elixir-phoenix-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:

• Search project AGENTS.md for the pattern keyword
• Check auto-memory files for similar lessons
• Read 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 ~/.codex/plugins/ are cached and get overwritten on updates. Always write to project or memory locations.

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

Step 4: Write the Lesson

For project AGENTS.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 ~/.codex/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 AGENTS.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 ~/.codex/plugins/ are cached and overwritten on updates
2. DO NOT duplicate existing lessons — always check AGENTS.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)

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