We are evaluating a lifecycle architecture for a local macOS application and would appreciate guidance on supported public APIs. Proposed architecture: A normally signed, non-root host application. One embedded XPC service with exactly one intended client. No application-created subprocesses inside the service. No privileged helper, persistent LaunchAgent, exported endpoints, private APIs, or reduced system security. One bounded operation per session. Failed or interrupted operations must not automatically be retried. Initial validation would use synthetic workloads only. Our current evaluation target is macOS 15.6 on Apple silicon, using the macOS 15.5 SDK. Please identify any relevant deployment-version limitations. The XPC overview (https://developer.apple.com/documentation/xpc) describes an embedded service as tied to its client's lifetime. We also understand that xpc_connection_cancel (https://developer.apple.com/documentation/xpc/xpc_connection_cancel(_:)) is asynchronous and non-preemptive; we are not treating connection cancellation as proof of service termination. We need clarification on these points: Client death and service startup Does the documented client-lifetime relationship cover client termination, including SIGKILL, during service startup before the first reply? Does it also cover an already running service that is blocked or stopped with SIGSTOP? Which behavior is guaranteed, and which timing or failure cases are intentionally unspecified? Timeout while the client remains alive What supported public mechanism should a normal application use to terminate its own unresponsive embedded service when an operation exceeds its deadline? We want to avoid PID enumeration, PID-reuse races, broad process-group signaling, and exporting a full task-control port. Is there a supported identity-bound termination mechanism? If not, what architecture does Apple recommend? A stopped or hung client remains alive, so we do not assume client-lifetime coupling handles that separate failure case. Observing termination Which public notification reliably identifies the exit of the particular service instance, as distinct from connection invalidation or a missing reply? Because launchd is the parent, the application cannot simply waitpid the service. Is reaping entirely launchd's responsibility, and what completion claim can the application legitimately make? Identity and required privileges Which public signing requirements, launch constraints, sandbox settings, or entitlements are necessary for this architecture? Please distinguish authentication before accepting work from constraints enforced before service code executes. We do not assume peer authentication also grants termination rights. Restart behavior After interruption, cancellation, client exit, or service failure, under what circumstances can launchd or subsequent XPC activity start a replacement service? What supported pattern prevents accidental resubmission or resumption of the same failed operation? We are not asking for hard real-time guarantees during kernel failure, or claiming that forced termination proves callback completion or explicit memory zeroization. If this combination of requirements is unsupported, identifying that boundary and the smallest supported architectural alternative would be a useful answer. Documentation references or a minimal public sample would be welcome.