Chrome and Computer Use fail with two concurrent macOS users on one Mac

What platform is your computer?

macOS on one MacBook with two macOS login users concurrently logged in via Fast User Switching. Both users run the ChatGPT desktop app / Codex.

What issue are you seeing?

When both macOS users run Codex concurrently on the same Mac, Chrome control and Computer Use become unavailable or appear to confuse the two active desktop sessions.

Chrome control fails before reading tabs or navigating:

Browser is not available: extension

The failure occurs even though Chrome is running and the ChatGPT Chrome Extension and native-host setup checks pass.

Computer Use independently fails on its first app-state request:

Sky Computer Use native pipe startup failed

Both failures reproduced in a fresh Codex task. The same errors also occurred repeatedly in a recent real task, including after resetting and reconnecting the tool sessions.

What steps can reproduce the bug?

1. Log in to macOS user A and run ChatGPT/Codex.
2. Use Fast User Switching to log in to macOS user B without logging out user A.
3. Run ChatGPT/Codex under user B as well.
4. Leave both desktop sessions logged in.
5. In a Codex task, try to use the Chrome plugin to access the current user's Chrome session.
6. Observe Browser is not available: extension.
7. In a Codex task, try to use Computer Use to inspect Chrome or list apps.
8. Observe Sky Computer Use native pipe startup failed.
9. Reset/reconnect the tool session and retry; the failures persist.

What is the expected behavior?

Each macOS login user's Codex instance, browser backend, and Computer Use helper should be isolated from the other logged-in user.

Both users should be able to run Codex concurrently without Chrome or Computer Use attaching to, discovering, or being blocked by the other user's session.

If concurrent Fast User Switching sessions are unsupported, Codex should detect the condition and display a clear, actionable message instead of generic extension/native-pipe errors.

Additional information

This may be related to:

• #32965 — two macOS users on one Mac are also confused in Remote/mobile thread routing
• #21672 — Chrome setup can fail when unrelated browser-use sessions exist
• #21719 — Chrome native host can attach to the wrong browser-use session
• #32340 — Computer Use can surface the same generic native-pipe startup error for other causes

No usernames, private thread content, or local machine diagnostics are included in this public report.