`akanjs/signal` declares the API boundary around services. Import it in `*.signal.ts` files to define endpoints, internal jobs, database slices, guards, middleware, request arguments, and registered server signals.

Guard classes decide whether a request can pass before endpoint or slice execution. `Public` always passes, `None` blocks, and `guard(name)` creates a named guard base class for app-specific rules.

Internal argument providers for advanced endpoints. `Req` gives the Bun request, `Res` gives the mutable response context, and `Ws` gives websocket subscription state and event hooks.

Middleware wraps endpoint execution. Built-ins include Logging, Cache, Timeout, and Retry, while custom middleware can read `SignalContext` and decide when to call `next()`.

Global registry for database and service signals. App `sig.ts` files register every module signal so serialized fetch metadata, server routes, and runtime signal lookup can be built consistently.