app-server: Add an ability to watch events in the test client (#13080)

Add a `watch` subcommand to `codex-app-server-test-client` binary to
help in manual testing of events flow.

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

@@ -18,6 +18,15 @@ cargo run -p codex-app-server-test-client -- \
 cargo run -p codex-app-server-test-client -- model-list
 ```
 
+## Watching Raw Inbound Traffic
+
+Initialize a connection, then print every inbound JSON-RPC message until you stop it with
+`Ctrl+C`:
+
+```bash
+cargo run -p codex-app-server-test-client -- watch
+```
+
 ## Testing Thread Rejoin Behavior
 
 Build and start an app server using commands above. The app-server log is written to `/tmp/codex-app-server-test-client/app-server.log`

codex-rs/app-server-test-client/src/lib.rs

@@ -188,6 +188,10 @@ enum CliCommand {
         /// Existing thread id to resume.
         thread_id: String,
     },
+    /// Initialize the app-server and dump all inbound messages until interrupted.
+    ///
+    /// This command does not auto-exit; stop it with SIGINT/SIGTERM/SIGKILL.
+    Watch,
     /// Start a V2 turn that elicits an ExecCommand approval.
     #[command(name = "trigger-cmd-approval")]
     TriggerCmdApproval {
@@ -291,6 +295,11 @@ pub fn run() -> Result<()> {
             let endpoint = resolve_endpoint(codex_bin, url)?;
             thread_resume_follow(&endpoint, &config_overrides, thread_id)
         }
+        CliCommand::Watch => {
+            ensure_dynamic_tools_unused(&dynamic_tools, "watch")?;
+            let endpoint = resolve_endpoint(codex_bin, url)?;
+            watch(&endpoint, &config_overrides)
+        }
         CliCommand::TriggerCmdApproval { user_message } => {
             let endpoint = resolve_endpoint(codex_bin, url)?;
             trigger_cmd_approval(&endpoint, &config_overrides, user_message, &dynamic_tools)
@@ -698,6 +707,16 @@ fn thread_resume_follow(
     client.stream_notifications_forever()
 }
 
+fn watch(endpoint: &Endpoint, config_overrides: &[String]) -> Result<()> {
+    let mut client = CodexClient::connect(endpoint, config_overrides)?;
+
+    let initialize = client.initialize()?;
+    println!("< initialize response: {initialize:?}");
+    println!("< streaming inbound messages until process is terminated");
+
+    client.stream_notifications_forever()
+}
+
 fn trigger_cmd_approval(
     endpoint: &Endpoint,
     config_overrides: &[String],