Fix Windows PTY teardown by preserving ConPTY ownership (#20685)

## Why

On Windows, background terminals could stay visible after their shell
process had already exited. The elevated runner waits for the PTY output
reader to reach EOF before it sends the final exit message, but the
ConPTY helper was reducing ownership down to raw handles too early. That
left the pseudoconsole's borrowed pipe handles alive past teardown, so
EOF never propagated and the session stayed `running`.

## What changed

- change `utils/pty/src/win/conpty.rs` to hand off owned ConPTY
resources instead of leaking only raw handles
- make `windows-sandbox-rs/src/conpty/mod.rs` keep the pseudoconsole
owner and the backing pipe handles together until teardown
- update the elevated runner and the legacy unified-exec backend to keep
that `ConptyInstance` alive, take only the specific pipe handles they
need, and drop the owner at teardown instead of trying to close a
detached pseudoconsole handle later

## Testing

- desktop app in `Auto-review`: 11 x `cmd /c "ping -n 3 google.com"` all
exited cleanly and did not accumulate in the UI
- desktop app in `Auto-review`: 5 x `cmd /c "ping -n 30 google.com"`
appeared in the UI and drained back out on their own

codex-rs/windows-sandbox-rs/src/elevated/command_runner_win.rs

@@ -15,7 +15,6 @@ use anyhow::Result;
 use codex_windows_sandbox::ErrorPayload;
 use codex_windows_sandbox::ExitPayload;
 use codex_windows_sandbox::FramedMessage;
-use codex_windows_sandbox::LaunchDesktop;
 use codex_windows_sandbox::LocalSid;
 use codex_windows_sandbox::Message;
 use codex_windows_sandbox::OutputPayload;
@@ -57,7 +56,6 @@ use windows_sys::Win32::Storage::FileSystem::FILE_GENERIC_READ;
 use windows_sys::Win32::Storage::FileSystem::FILE_GENERIC_WRITE;
 use windows_sys::Win32::Storage::FileSystem::OPEN_EXISTING;
 use windows_sys::Win32::System::Console::COORD;
-use windows_sys::Win32::System::Console::ClosePseudoConsole;
 use windows_sys::Win32::System::Console::ResizePseudoConsole;
 use windows_sys::Win32::System::JobObjects::AssignProcessToJobObject;
 use windows_sys::Win32::System::JobObjects::CreateJobObjectW;
@@ -87,8 +85,8 @@ struct IpcSpawnedProcess {
     stdout_handle: HANDLE,
     stderr_handle: HANDLE,
     stdin_handle: Option<HANDLE>,
+    conpty_owner: Option<codex_windows_sandbox::ConptyInstance>,
     hpc_handle: Option<HANDLE>,
-    _desktop_owner: Option<LaunchDesktop>,
     _pipe_handles: Option<PipeSpawnHandles>,
 }
 
@@ -263,11 +261,11 @@ fn spawn_ipc_process(req: &SpawnRequest) -> Result<IpcSpawnedProcess> {
 
     let effective_cwd = effective_cwd(&req.cwd, Some(log_dir.as_path()));
 
+    let mut conpty_owner = None;
     let mut hpc_handle: Option<HANDLE> = None;
-    let mut desktop_owner = None;
     let mut pipe_handles = None;
     let (pi, stdout_handle, stderr_handle, stdin_handle) = if req.tty {
-        let (pi, conpty) = codex_windows_sandbox::spawn_conpty_process_as_user(
+        let (pi, mut conpty) = codex_windows_sandbox::spawn_conpty_process_as_user(
             h_token.raw(),
             &req.command,
             &effective_cwd,
@@ -275,9 +273,10 @@ fn spawn_ipc_process(req: &SpawnRequest) -> Result<IpcSpawnedProcess> {
             req.use_private_desktop,
             Some(log_dir.as_path()),
         )?;
-        let (hpc, input_write, output_read, desktop) = conpty.into_raw();
-        hpc_handle = Some(hpc);
-        desktop_owner = desktop;
+        hpc_handle = conpty.raw_handle();
+        let input_write = conpty.take_input_write();
+        let output_read = conpty.take_output_read();
+        conpty_owner = Some(conpty);
         let stdin_handle = if req.stdin_open {
             Some(input_write)
         } else {
@@ -323,8 +322,8 @@ fn spawn_ipc_process(req: &SpawnRequest) -> Result<IpcSpawnedProcess> {
         stdout_handle,
         stderr_handle,
         stdin_handle,
+        conpty_owner,
         hpc_handle,
-        _desktop_owner: desktop_owner,
         _pipe_handles: pipe_handles,
     })
 }
@@ -526,6 +525,7 @@ pub fn main() -> Result<()> {
     let pi = ipc_spawn.pi;
     let stdout_handle = ipc_spawn.stdout_handle;
     let stderr_handle = ipc_spawn.stderr_handle;
+    let mut conpty_owner = ipc_spawn.conpty_owner;
     let stdin_handle = ipc_spawn.stdin_handle;
     let hpc_handle = Arc::new(StdMutex::new(ipc_spawn.hpc_handle));
 
@@ -605,13 +605,10 @@ pub fn main() -> Result<()> {
         }
     }
 
-    if let Ok(mut guard) = hpc_handle.lock()
-        && let Some(hpc) = guard.take()
-    {
-        unsafe {
-            ClosePseudoConsole(hpc);
-        }
+    if let Ok(mut guard) = hpc_handle.lock() {
+        let _ = guard.take();
     }
+    drop(conpty_owner.take());
 
     let _ = out_thread.join();
     if let Some(thread) = err_thread {