No Angular or DOM imports — safe for pure-Node (backend) bundles.

Handlers extend Service, receive a rendering-engine facade as a protected readonly property and implement handle, either returning the resolved value or throwing (a CancelledError when the user cancels mid-request). Lookup and dispatch are static: @userRequest(reference) records the class as metadata and UserRequestHandler.getHandler(reference) / UserRequestHandler.handle(request, renderingEngine) resolve and run it, so no process-wide registry instance is needed.