fix: remove PR_SET_PDEATHSIG that kills Chrome after ~10s idle (#1157) (#1173)

v0.24.1 introduced `prctl(PR_SET_PDEATHSIG, SIGKILL)` in #1137 to kill Chrome
when the daemon dies. However, `PR_SET_PDEATHSIG` tracks the **thread** that
called `fork()`, not the process (`prctl(2)` documents this). Chrome is spawned
via `tokio::task::spawn_blocking`, whose threads are reaped after ~10 seconds of
idle time. When the blocking thread exits, the kernel sends SIGKILL to Chrome
even though the daemon is still alive.

Symptoms reported in #1157:
- `tab list` shows `about:blank` after a few seconds
- `snapshot` returns an empty page
- All Chrome processes exit ~9 seconds after launch
- Any workflow involving navigation or waiting breaks

The fix removes `PR_SET_PDEATHSIG` from the Chrome `pre_exec` hook. Orphan
cleanup is already handled by the process-group kill (`kill(-pgid, SIGKILL)`) in
`ChromeProcess::kill()`, which runs via daemon signal handlers, `close_notify`,
idle timeout, and `Drop`.

Fixes #1157

cli/src/native/cdp/chrome.rs

@@ -351,23 +351,18 @@ fn try_launch_chrome(chrome_path: &Path, options: &LaunchOptions) -> Result<Chro
     // Place Chrome in its own process group so we can kill the entire tree
     // (main process + GPU/renderer/utility/crashpad helpers) with a single
     // killpg(), preventing orphaned processes (issue #1113).
+    //
+    // NOTE: Do NOT use PR_SET_PDEATHSIG here. Chrome is spawned via
+    // tokio::task::spawn_blocking, and PR_SET_PDEATHSIG fires when the
+    // *thread* that forked the child exits, not the process. Tokio reaps
+    // idle blocking threads after ~10s, which kills Chrome (issue #1157).
     #[cfg(unix)]
     {
         use std::os::unix::process::CommandExt;
         // SAFETY: pre_exec runs between fork() and exec() in the child.
-        // Both prctl and setpgid are async-signal-safe.
+        // setpgid is async-signal-safe.
         unsafe {
             cmd.pre_exec(|| {
-                // On Linux, ask the kernel to send SIGKILL to this process
-                // when the parent (daemon) dies for any reason, including
-                // SIGKILL. This is the most robust orphan prevention
-                // available and has no macOS equivalent.
-                #[cfg(target_os = "linux")]
-                {
-                    libc::prctl(libc::PR_SET_PDEATHSIG, libc::SIGKILL);
-                }
-                // Create a new process group (PGID = own PID) so the
-                // daemon can kill the entire Chrome tree in one call.
                 libc::setpgid(0, 0);
                 Ok(())
             });