// SPDX-License-Identifier: Apache-2.0
// Copyright (c) 2025 ReifyDB
//! Subsystem trait surface: the contract every `sub-*` crate implements so the runtime supervisor can start, stop,
//! and health-check them through a uniform handle. The trait is intentionally minimal so a subsystem can hide its
//! own internal architecture while still participating in lifecycle management. New subsystems implement this trait
//! to be discoverable by the supervisor.