fix: use socket connectivity alone instead combining it with PID check for daemon liveness (#879)

.changeset/fix-pid-namespace.md

@@ -0,0 +1,5 @@
+---
+"agent-browser": patch
+---
+
+Fix daemon detection for PID namespace isolation (e.g. `unshare`). Use socket connectivity as the sole liveness check instead of `kill(pid, 0)`, which fails when the caller cannot see the daemon's PID.

cli/src/connection.rs

@@ -150,42 +150,6 @@ fn get_port_for_session(session: &str) -> u16 {
     49152 + ((hash.unsigned_abs() as u32 % 16383) as u16)
 }
 
-#[cfg(unix)]
-fn is_daemon_running(session: &str) -> bool {
-    let pid_path = get_pid_path(session);
-    if !pid_path.exists() {
-        return false;
-    }
-    if let Ok(pid_str) = fs::read_to_string(&pid_path) {
-        if let Ok(pid) = pid_str.trim().parse::<i32>() {
-            unsafe {
-                if libc::kill(pid, 0) == 0 {
-                    return true;
-                }
-                // EPERM means the process exists but we lack permission to
-                // signal it (e.g. inside a macOS sandbox). Only ESRCH means
-                // the process is genuinely gone.
-                return std::io::Error::last_os_error().raw_os_error() != Some(libc::ESRCH);
-            }
-        }
-    }
-    false
-}
-
-#[cfg(windows)]
-fn is_daemon_running(session: &str) -> bool {
-    let pid_path = get_pid_path(session);
-    if !pid_path.exists() {
-        return false;
-    }
-    let port = get_port_for_session(session);
-    TcpStream::connect_timeout(
-        &format!("127.0.0.1:{}", port).parse().unwrap(),
-        Duration::from_millis(100),
-    )
-    .is_ok()
-}
-
 fn daemon_ready(session: &str) -> bool {
     #[cfg(unix)]
     {
@@ -315,8 +279,10 @@ fn apply_daemon_env(cmd: &mut Command, session: &str, opts: &DaemonOptions) {
 }
 
 pub fn ensure_daemon(session: &str, opts: &DaemonOptions) -> Result<DaemonResult, String> {
-    // Check if daemon is running AND responsive
+    // Socket connectivity is the sole liveness check — no PID check — so
-    if is_daemon_running(session) && daemon_ready(session) {
+    // callers in a different PID namespace (e.g. unshare) can still reuse
+    // an existing daemon they can reach over the socket.
+    if daemon_ready(session) {
         // Double-check it's actually responsive by waiting and checking again
         // This handles the race condition where daemon is shutting down
         // (daemon has a 100ms shutdown delay, so we wait longer)