Phx Init

---
name: phx-init
description: Initialize plugin in a project — install Iron Laws, auto-activation;
  Use when setting up or updating the plugin.
---

# Plugin Initialization

Install the Elixir/Phoenix plugin's behavioral instructions into the project's CLAUDE.md.

## Usage

```
$elixir-phoenix:phx-init           # First-time installation
$elixir-phoenix:phx-init --update  # Update existing installation with latest rules
```

## Iron Laws

1. **NEVER overwrite content outside plugin markers** — User-written CLAUDE.md rules must be preserved verbatim
2. **Always detect stack before generating** — Never assume Phoenix/Ecto versions
3. **Always validate after installation** — Verify markers present and stack correct

## Workflow

### Step 1: Check Existing CLAUDE.md

Use Glob to check if `CLAUDE.md` exists. Then use Grep to check for existing `ELIXIR-PHOENIX-PLUGIN:START` marker in `CLAUDE.md`.

### Step 2: Detect Project Stack

Scan the project to customize the injected instructions:

Read `mix.exs` and use Grep to extract:

- Phoenix version: search for `phoenix.*"~>` in `mix.exs`
- Ecto version: search for `ecto.*"~>` in `mix.exs`
- Oban: search for `"oban"` and `"oban_pro"` in `mix.exs`
- Frameworks: search for `"ash"`, `"surface"` in `mix.exs`
- Tidewave: search for `"tidewave"` in `mix.exs`
- Project size: use Glob to count `lib/**/*.ex` files

### Step 3: Handle Installation Modes

**Mode A: Fresh Install** (no CLAUDE.md or no markers)

1. Create/append to CLAUDE.md
2. Insert full behavioral instructions between markers
3. Include only relevant sections based on detected stack

**Mode B: Update** (`--update` flag or markers exist)

1. Find content between `<!-- ELIXIR-PHOENIX-PLUGIN:START -->` and `<!-- ELIXIR-PHOENIX-PLUGIN:END -->`
2. Replace with latest behavioral instructions
3. Preserve everything outside the markers

**CRITICAL: NEVER overwrite or delete existing CLAUDE.md content outside the plugin markers** — user-written rules, project conventions, and other plugin sections must be preserved verbatim

### Step 4: Generate Content

Write the following structure to CLAUDE.md:

```markdown
<!-- ELIXIR-PHOENIX-PLUGIN:START -->
<!-- Last updated: {date} | Plugin version: 1.0 | Stack: Phoenix {version}, Ecto {version}, {optional: Oban, Tidewave} -->

# Elixir/Phoenix Plugin - Auto-Activation Rules

{Include all sections from the Content Template below, filtered by detected stack}

<!-- ELIXIR-PHOENIX-PLUGIN:END -->
```

### Step 4b: Offer Codex Review Guidelines (optional)

If `command -v codex` succeeds (or the user asks): offer to install a
managed `## Review guidelines` block into the project's `AGENTS.md` —
honored by BOTH `codex exec review` locally and the Codex cloud PR
reviewer. Follow the install rules and exact block in
`references/codex-review-guidelines.md`: markers
`ELIXIR-PHOENIX-REVIEW-GUIDELINES:START/END`, upsert in place on
`--update`, never touch content outside markers, and STOP to ask if an
unmanaged `## Review guidelines` section already exists. When codex is
absent and not requested, skip silently — never mention codex to users
who don't have it.

### Step 5: Output Summary

```
✅ Elixir/Phoenix plugin initialized

Detected stack:
- Phoenix {version}
- Ecto {version}
- {Oban standard | Oban Pro | not detected}
- {Tidewave ✓ | Tidewave not detected}
- {Ash Framework detected - Ecto patterns disabled | not detected}

Added to CLAUDE.md:
- Auto-activation rules (complexity detection, interview mode)
- Agent trigger patterns ({n} agents available)
- Reference auto-loading ({n} reference docs)
- Iron Laws enforcement ({n} laws)
- Verification rules
{- Codex review guidelines → AGENTS.md (only if installed in Step 4b)}

Run $elixir-phoenix:phx-init --update after plugin updates.
Run $elixir-phoenix:phx-audit for a full project health check.
```

## Content Template

The exact content to inject is in `references/injectable-template.md`.

**Key structure:**

1. **Routing table** — which `$elixir-phoenix:phx-*` command fits which kind of request
2. **Iron Laws** — STOP behavior on violations
3. **Conditional Sections** — Include based on detected stack:
   - `{OBAN_SECTION}` — If Oban detected (not Pro)
   - `{OBAN_PRO_SECTION}` — If Oban Pro detected
   - `{ASH_SECTION}` — If Ash Framework detected
   - `{TIDEWAVE_SECTION}` — If Tidewave detected
4. **Verification** — Mandatory after code changes
5. **Quick Reference** — Skill routing table

**Placeholder substitution:**

| Placeholder | Source |
|-------------|--------|
| `{DATE}` | Current date |
| `{PHOENIX_VERSION}` | From mix.exs |
| `{ECTO_VERSION}` | From mix.exs |
| `{OPTIONAL_STACK}` | Detected optional deps |

See `references/injectable-template.md` for full template with all placeholders and conditional sections.

## Validation

After running `$elixir-phoenix:phx-init`:

1. Check CLAUDE.md contains markers
2. Verify detected stack matches actual project
3. New session should:
   - Auto-detect complexity when given tasks
   - Stop on Iron Law violations
   - Offer relevant workflows based on task

## Error Handling

| Scenario | Action |
|----------|--------|
| CLAUDE.md read-only | Error: "Cannot modify CLAUDE.md - check permissions" |
| Markers corrupted | Warn, offer to remove and reinstall |
| Unknown Phoenix version | Use conservative defaults (all features enabled) |
| Not an Elixir project | Error: "No mix.exs found - is this an Elixir project?" |

## Relationship to Other Commands

| Command | When to Use |
|---------|-------------|
| `$elixir-phoenix:phx-init` | First time, or after plugin updates |
| `$elixir-phoenix:phx-audit` | Periodic project health check |
| `$elixir-phoenix:phx-verify` | After code changes |