engine

name	engine
type	persona
tags	["personas"]
license	MIT
description	Complete Rails engine development loop with hard gates: scaffold engine structure with isolate_namespace and verify gemspec validation → set up dummy app and verify tests run with exit 0 → NEVER integrate engine into host app before engine tests pass standalone, namespace is isolated, migrations won't conflict, and dependencies are declared → code review and dependency auditing → release with SemVer, changelog, and upgrade notes; phases authoring→testing→implementation/review→documentation/release. Use when creating, extracting, or maintaining Rails engines. Trigger: create engine, extract engine, engine release, engine testing, mountable engine, gem extraction.
metadata	{"version":"1.0.0","user-invocable":"true","entry_point":"Invoke when creating, extracting, or maintaining Rails engines","phases":"Phase 1: Engine Authoring, Phase 2: Testing Setup, Phase 3: Implementation & Review, Phase 4: Documentation & Release","hard_gates":"Engine Structure Check, Tests Run, Isolation Before Integration","dependencies":[{"source":"self","skills":["create-engine","test-engine","review-engine","document-engine","release-engine","upgrade-engine"]},{"source":"ruby-core-skills","skills":["write-yard-docs","tdd-process"]}],"keywords":"rails, engine, agent, gem, release, testing, extraction"}

Phase 1: Engine Authoring

1. skills/engines/create-engine (sub-skill — invoke separately) — Design and scaffold namespace isolation, directory structure, and gemspec configuration

Kickoff command:

rails plugin new my_engine --mountable --test-framework=rspec

Key files to verify after scaffolding:

• lib/my_engine/engine.rb — must contain isolate_namespace MyEngine
• lib/my_engine/version.rb
• my_engine.gemspec — must pass gem specification validation
• test/dummy/ — dummy app present

HARD GATE — Engine Structure Check:

grep -r 'module MyEngine' lib/my_engine/engine.rb
ruby -e "require 'rubygems'; spec = Gem::Specification.load('my_engine.gemspec'); puts spec.validate"
grep 'isolate_namespace\|engine.config.isolate_namespace' lib/my_engine/engine.rb

If structure check FAILS: Return to create-engine and fix.

---

Phase 2: Testing Setup

1. skills/engines/test-engine (sub-skill — invoke separately) — Set up dummy app, spec helpers, factory isolation, and test database

2. Write initial characterization tests:

   • Test engine mounting
   • Test generators if any
   • Test core functionality

Run tests from engine root:

cd my_engine && bundle exec rspec

HARD GATE — Tests Run:

bundle exec rspec --format progress 2>&1 | tail -5

Must show no load errors and exit 0.

If load errors appear: Consult the test-engine sub-skill for ordered troubleshooting steps.

HARD GATE — Isolation Before Integration:

NEVER integrate engine into host app before:

1. Engine tests pass standalone
2. Namespace properly isolated
3. Migrations won't conflict
4. Dependencies clearly declared

---

Phase 3: Implementation & Review

1. Implement features using:

   • tdd agent for complex features
   • Individual skills for simple additions

2. skills/engines/review-engine (sub-skill — invoke separately)

3. skills/engines/upgrade-engine (sub-skill — invoke separately)

Check gem dependencies:

bundle exec rake dependencies
bundle exec bundler-audit check --update

---

Phase 4: Documentation & Release

1. skills/engines/document-engine (sub-skill — invoke separately) — Installation, configuration, usage examples, changelog

2. skills/engines/release-engine (sub-skill — invoke separately) — Version bump (SemVer), changelog, upgrade notes, git tag

Release commands:

gem build my_engine.gemspec
gem push my_engine-1.0.0.gem
git tag v1.0.0 && git push origin v1.0.0

Optional: 3. skills/engines/create-engine-installer — Idempotent rails g my_engine:install generator for host app configuration

Output: Published gem or releasable GitHub repository.

---

Quick Reference

New engine?        → create-engine → test-engine
Extract from app?  → extract-engine → create-engine
Release engine?    → review-engine → release-engine
Not sure?          → skill-router

---

Common Anti-Patterns

Anti-Pattern	Fix
Namespace leakage — ::MyEngine instead of MyEngine::	Verify isolate_namespace MyEngine in engine.rb
Migration conflicts — Migrations outside engine dir or missing path config	Run engine migrations in isolation via dummy app
Missing gemspec dependencies — Runtime gems in Gemfile but not in .gemspec	Run bundle exec rake dependencies and bundler-audit check at Phase 3 end
Dummy app load errors — Missing require or incorrect spec_helper	Use test-engine sub-skill diagnostic steps