Agent Skills: action-controller

Expert guidance for writing Rails controllers with Action Controller. Use when writing controller actions, strong parameters, before_action filters, rendering responses, redirects, flash messages, sessions, cookies, rescue_from error handling, streaming, CSRF protection, or HTTP authentication. Covers params permitting (especially nested params — the #1 source of agent bugs), callbacks, request/response objects, and security. Trigger on "controller", "action", "strong parameters", "params", "before_action", "redirect", "render", "flash", "session", "cookies", "rescue_from", "CSRF", "permit", "expect", "filters", "callbacks".