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/actions.rs

@@ -993,9 +993,11 @@ pub async fn execute_command(cmd: &Value, state: &mut DaemonState) -> Value {
             | "device_list"
     );
     if !skip_launch {
-        // Check if existing connection is stale and needs re-launch
-        let needs_launch = if let Some(ref mgr) = state.browser {
-            !mgr.is_connection_alive().await
+        // Check if existing connection is stale and needs re-launch.
+        // First do a fast, non-blocking check: did the browser process crash/exit?
+        // This avoids a 3-second CDP timeout when Chrome is already dead.
+        let needs_launch = if let Some(ref mut mgr) = state.browser {
+            mgr.has_process_exited() || !mgr.is_connection_alive().await
         } else {
             true
         };
@@ -1356,11 +1358,12 @@ async fn handle_launch(cmd: &Value, state: &mut DaemonState) -> Result<Value, St
         .and_then(|v| v.as_bool())
         .unwrap_or(false);
 
-    // Relaunch logic: check if we can reuse the existing connection
-    let needs_relaunch = if let Some(ref mgr) = state.browser {
+    // Relaunch logic: check if we can reuse the existing connection.
+    // Fast process-exit check first to avoid expensive CDP timeout.
+    let needs_relaunch = if let Some(ref mut mgr) = state.browser {
         let is_external = cdp_url.is_some() || cdp_port.is_some() || auto_connect;
         let was_external = mgr.is_cdp_connection();
-        is_external != was_external || !mgr.is_connection_alive().await
+        is_external != was_external || mgr.has_process_exited() || !mgr.is_connection_alive().await
     } else {
         true
     };

cli/src/native/browser.rs

@@ -180,6 +180,14 @@ impl BrowserProcess {
             BrowserProcess::Lightpanda(p) => p.kill(),
         }
     }
+
+    /// Non-blocking check whether the browser process has exited.
+    pub fn has_exited(&mut self) -> bool {
+        match self {
+            BrowserProcess::Chrome(p) => p.has_exited(),
+            BrowserProcess::Lightpanda(_) => false,
+        }
+    }
 }
 
 pub struct BrowserManager {
@@ -643,6 +651,17 @@ impl BrowserManager {
         }
     }
 
+    /// Non-blocking check whether the locally-launched browser process has exited
+    /// (crashed or terminated). Also reaps the zombie if it has exited.
+    /// Returns false for external CDP connections (no child process to monitor).
+    pub fn has_process_exited(&mut self) -> bool {
+        if let Some(ref mut process) = self.browser_process {
+            process.has_exited()
+        } else {
+            false
+        }
+    }
+
     pub fn get_cdp_url(&self) -> &str {
         &self.ws_url
     }

cli/src/native/cdp/chrome.rs

@@ -17,6 +17,17 @@ impl ChromeProcess {
         let _ = self.child.wait();
     }
 
+    /// Returns the OS process ID of the Chrome child process.
+    pub fn id(&self) -> u32 {
+        self.child.id()
+    }
+
+    /// Non-blocking check whether Chrome has exited.
+    /// Returns `true` if the process has exited (and reaps it), `false` if still running.
+    pub fn has_exited(&mut self) -> bool {
+        matches!(self.child.try_wait(), Ok(Some(_)) | Err(_))
+    }
+
     /// Wait for Chrome to exit on its own (after Browser.close CDP command),
     /// falling back to kill() if it doesn't exit within the timeout.
     /// This allows Chrome to flush cookies and other state to the user-data-dir.

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,