Implement native client core lifecycle (#51)

README.md

@@ -250,3 +250,15 @@ visual-parameter values. Native skeleton traversal, alias lookup, expanded mesh
 joint lists, custom XML loading, attention indexing, and archetype lookup now
 implement the mapped behavior directly in Rust. Each checked-in catalog retains
 its own input hash and license provenance.
+
+### Milestone 08
+
+The native client core now provides the exact grouped `Settings` defaults from
+the golden C# implementation, validates endpoints, durations, limits, cache
+policy, and download policy, and exposes typed configuration and lifecycle
+errors. `GridClient` construction and drop have no network side effects and do
+not create an async runtime. Explicitly composed services share a cancellation
+token and are shut down idempotently in network, manager, HTTP, then rate-limiter
+order. Injected clocks support deterministic tests, while `Debug` output omits
+endpoint values and service internals. The ownership and executor requirements
+are documented in [`docs/client-core.md`](docs/client-core.md).