[Windows][IAB] Agent-created tab disappears from tabs.list while Browser instance remains active

What version of the Codex App are you using (From “About Codex” dialog)?

26.826.12353

What subscription do you have?

Not provided

What platform is your computer?

Windows (affected PC; exact Windows build not provided)

What issue are you seeing?

Submitted from a separate healthy PC on behalf of the affected Windows PC.
All environment and reproduction details below refer to the affected PC.

Core issue: Codex in-app Browser / IAB tab registration state is unstable.

A tab can remain visibly open in the IAB UI while the Browser control layer reports:

openTabs = 1
tabs.list = 0

The visible tab and current task were confirmed to belong to the same IAB instance. Therefore, this is not an instance mismatch.

A visible IAB tab remained open in an authenticated internal ERP web application. A new tab created through the supported Browser API initially appeared in tabs.list, but the same agent-created tab disappeared from tabs.list again before the stability test began. The Browser instance remained unchanged. No Browser runtime reset or white screen was observed during this reproduction.

What steps can reproduce the bug?

1. On the affected Windows PC, isolate the previous .codex state.
2. Isolate the previous AppData\Local\OpenAI\Codex runtime state.
3. Uninstall Codex.
4. Reboot Windows.
5. Reinstall Codex from the Microsoft Store.
6. Do not restore the previous Skill, old config.toml, old Browser state, or old plugin cache / marketplace state.
7. Disable the Chrome backend, Computer Use, and Full CDP.
8. Open a visible IAB tab in an authenticated internal ERP web application.
9. Observe openTabs = 1 and tabs.list = 0.
10. Confirm that the current task and the visible IAB tab belong to the same IAB instance.
11. Create a new tab through the supported Browser API.
12. Immediately observe tabs.list = 1.
13. Before the stability test begins, observe that the same agent-created tab disappears from tabs.list while remaining visibly open in IAB; observe tabs.list = 0.
14. Confirm that the Browser instance remains unchanged, with no runtime reset and no white screen.

What is the expected behavior?

If an IAB tab was successfully created and registered, remains visibly open, belongs to the active Browser instance, has not been explicitly closed, and the Browser runtime has not reset, it should remain visible in tabs.list.

The visible/open tab state and the registration/claim state should not diverge unexpectedly.

Additional information

Affected-device versions:

• Codex About Version: 26.826.12353
• Windows AppX Package: 26.820.10647.0
• Bundled Browser plugin: 26.820.80927
• Active Browser plugin: 26.820.80927

Clean-room reproduction was verified after isolating previous .codex state and previous AppData\Local\OpenAI\Codex runtime state, uninstalling Codex, rebooting Windows, reinstalling from the Microsoft Store, and restoring no previous Skill, config.toml, Browser state, plugin cache, or marketplace state.

Browser control chain verified on the affected machine:

• Browser plugin initialized = yes
• IAB backend initialized = yes
• Browser service running = yes
• IAB instance exists = yes
• Trusted Browser control tool exposed = yes
• Browser Node REPL available = yes
• Browser client attached to task = yes
• No HTTP 401 observed
• No HTTP 403 observed
• No policy verification failure observed
• No entitlement failure observed

Browser bundle consistency:

• APP_BUNDLED_BROWSER=26.820.80927
• ACTIVE_BROWSER=26.820.80927

Therefore, this is not a stale Browser plugin version mismatch.

No logs or attachments are included; the report contains only sanitized reproduction facts. No healthy-PC diagnostic data is included.

Start by reproducing the Windows flow through the supported Browser API and compare the IAB visible tab with openTabs and tabs.list after creation. Trace the tab registration and removal lifecycle for the active Browser instance; done means an unclosed, runtime-stable agent-created tab remains in tabs.list.