What a system is given once, when it is registered.
Phase 1 exposes only the registry (so a system can register a helper system
or hold a handle for its own teardown). Later phases add fields; this is an
interface precisely so that widening it is source-compatible.
What a system is given once, when it is registered.
Phase 1 exposes only the registry (so a system can register a helper system or hold a handle for its own teardown). Later phases add fields; this is an interface precisely so that widening it is source-compatible.