描述
ALWAYS `render inertia: { key: data }` to pass data as props — instance variables are NOT auto-passed (only alba-inertia does that). Rails controller patterns for Inertia.js: render inertia, prop types (defer, optional, merge, scroll), shared data, flash, PRG redirects, validation errors. Use when writing controllers that load data, display records, or serve Inertia responses. CRITICAL: external URLs (Stripe/OAuth) MUST use inertia_location, NEVER redirect_to.