app-server-test-client websocket client and thread tools (#11755)

- add websocket endpoint mode with default ws://127.0.0.1:4222 while
keeping stdio codex-bin path compatibility
- add thread-resume (follow stream) and thread-list commands for manual
thread lifecycle testing
- quickstart docs

codex-rs/app-server-test-client/README.md

@@ -1,2 +1,19 @@
 # App Server Test Client
-Exercises simple `codex app-server` flows end-to-end, logging JSON-RPC messages sent between client and server to stdout.
+Quickstart for running and hitting `codex app-server`.
+
+## Quickstart
+
+Run from `<reporoot>/codex-rs`.
+
+```bash
+# 1) Build debug codex binary
+cargo build -p codex-cli --bin codex
+
+# 2) Start websocket app-server in background
+cargo run -p codex-app-server-test-client -- \
+  --codex-bin ./target/debug/codex \
+  serve --listen ws://127.0.0.1:4222 --kill
+
+# 3) Call app-server (defaults to ws://127.0.0.1:4222)
+cargo run -p codex-app-server-test-client -- model-list
+```