Guide for creating, updating, and deprecating hybrid cloud RPC services in Sentry. Use when asked to "add RPC method", "create RPC service", "hybrid cloud service", "new RPC model", "deprecate RPC method", "remove RPC endpoint", "cross-silo service", "cell RPC", or "control silo service". Covers service scaffolding, method signatures, RPC models, cell resolvers, testing, and safe deprecation workflows.