rails

REQUIRED BACKGROUND: This skill depends_on: [clean-code, backend-fundamentals]. clean-code gives universal code quality (fail-closed errors, typed exceptions, self-documenting code, error-path tests); backend-fundamentals gives stack-agnostic backend patterns (services, idempotency, envelopes, N+1, migrations, auth). This skill adds ONLY Ruby on Rails-specific layering on top.

rails

Layer contract (matches structure.tree)

Controllers stay thin and transport-aware; models stay transport-free (no params, no render) so they are unit-testable and the business logic survives a transport swap (REST → GraphQL → ActionCable).

Routes & controllers (thin)

• config/routes.rb is the single routing table — prefer resources/resource over hand-rolled match; one URL, one place.
• An action: strong-parameter the input (params.require(:x).permit(:a, :b)) → call ONE model method → render. No business branching, no multi-query loops.
• Subclass ApplicationController; never rescue-and-shape inside an action — raise a typed error and let the global chain map it.
• before_action filters load records / enforce auth; keep them in concerns when three controllers share them (rule of three), not copy-pasted.

Models (ActiveRecord — the only layer that thinks)

• Business logic, scopes, and validates live on the model; a controller that validates by hand is a layering violation.
• Persist with save!/create!/update! so a failure raises and the rescue_from chain maps it — silent save that returns false hides errors.
• Migrations are reversible (change, or paired up/down); schema and data migrations stay in separate files. The agent writes them; the user runs db:migrate.