fix(rust-client): async CA file read; typed ping/session-state/worker-info/drain-events

clients/rust/README.md

@@ -178,6 +178,18 @@ redaction. Per-item bulk failures are reported inside each result entry
 `invoke_raw` / `client.invoke_raw` escape hatch performs neither check and
 returns the unvalidated reply.
 
+### Diagnostic commands
+
+`Session` wraps the worker diagnostic commands as typed calls: `ping(message)`
+(returns `()` on success), `get_session_state()` (returns `SessionState`),
+`get_worker_info()` (returns `WorkerInfoReply`: pid, version, MXAccess
+ProgID/CLSID) and `drain_events(max_events)` (returns `Vec<MxEvent>`; the reply
+is bounded server-side, so drain until an empty result). A reply missing its
+expected payload surfaces as `Error::MalformedReply`.
+
+TLS note: `ClientOptions::with_ca_file` is read asynchronously (`tokio::fs`)
+during `connect`, so connecting no longer blocks the executor thread.
+
 ## Event Streaming And Reconnect-Replay Gaps
 
 `session.events()` / `session.events_after(after_worker_sequence)` (and the