fix: reap zombie Chrome process and fast-detect crash for auto-restart (#1023)

When Chrome crashes (e.g. SIGTRAP from CHECK() assertion), the daemon
now:

1. Reaps the zombie immediately via a SIGCHLD handler in the event loop
   that calls waitpid(-1, WNOHANG)
2. Detects the crash instantly on the next command via a non-blocking
   try_wait() check (has_process_exited), avoiding the 3-second CDP
   timeout that is_connection_alive() would incur
3. Auto-relaunches Chrome transparently for the caller

Fixes #1017

Co-authored-by: ctate <366502+ctate@users.noreply.github.com>

cli/src/native/daemon.rs

@@ -109,6 +109,12 @@ async fn run_socket_server(
     let (reset_tx, mut reset_rx) = mpsc::channel::<()>(64);
     let reset_tx = idle_timeout_ms.map(|_| Arc::new(reset_tx));
 
+    // Listen for SIGCHLD to reap zombie child processes (e.g. crashed Chrome).
+    // Without this, a crashed Chrome becomes <defunct> and is never reaped until
+    // the daemon exits.
+    let mut sigchld = signal::unix::signal(signal::unix::SignalKind::child())
+        .map_err(|e| format!("Failed to install SIGCHLD handler: {}", e))?;
+
     loop {
         let sleep_future = idle_timeout_ms.map(|ms| tokio::time::sleep(Duration::from_millis(ms)));
         let mut sleep_pin = sleep_future.map(Box::pin);
@@ -128,6 +134,12 @@ async fn run_socket_server(
                     }
                 }
             }
+            _ = sigchld.recv() => {
+                // Reap all zombie children. The browser will be re-launched
+                // automatically on the next command via the has_process_exited()
+                // check in execute_command.
+                reap_children();
+            }
             _ = async {
                 if let Some(ref mut s) = sleep_pin {
                     s.as_mut().await
@@ -157,6 +169,17 @@ async fn run_socket_server(
     Ok(())
 }
 
+/// Reap all zombie child processes by calling waitpid(-1, WNOHANG) in a loop.
+#[cfg(unix)]
+fn reap_children() {
+    loop {
+        let result = unsafe { libc::waitpid(-1, std::ptr::null_mut(), libc::WNOHANG) };
+        if result <= 0 {
+            break;
+        }
+    }
+}
+
 #[cfg(windows)]
 async fn run_socket_server(
     socket_path: &PathBuf,