Cursor 3.15+: Codex sidebar with session history fails to open; no Activity Bar fallback

What version of the IDE extension are you using?

26.803.61601 (also reproduced with 26.803.41515)

What subscription do you have?

ChatGPT (same account works in Cursor 3.14.27; this is a UI/host compatibility bug, not auth)

Which IDE are you using?

Cursor

What platform is your computer?

Linux 6.8.0-137-generic x86_64 x86_64 (Ubuntu 24.04)

What issue are you seeing?

On Cursor 3.15.6+, the Codex IDE extension activates and the app-server starts, but the real Codex sidebar never opens. That is the view that has session history, thread switching, and resume.

What still works:

• Codex: New Codex Agent opens a one-off editor tab with no history / no session picker / no way to resume another thread from the UI.

What does not work:

• Codex: Open Codex Sidebar
• Activity Bar Codex icon (it is hidden)
• Searching or switching previous sessions from the extension UI

Claude Code in the same Cursor build still works as an independent panel (history and sessions included). It is not docked in Cursor's Agents window either; it just falls back to its own Activity Bar container.

This is distinct from "Codex cannot live in Cursor's Agents / Secondary Side Bar". The request here is only: open a functional independent Codex UI, the same way Claude Code still can.

Logs (PII redacted):

[error] [openai.chatgpt]: View containers cannot be contributed to the Secondary Side Bar in Cursor. It is reserved for Cursor's agent UI. Contribute to 'activitybar' or 'panel' instead.
[warning] [openai.chatgpt]: View container 'codexSecondaryViewContainer' does not exist and all views registered to it will be added to 'Explorer'.

[info] Activating Codex extension
[info] [CodexMcpConnection] Spawning codex app-server
[info] [CodexMcpConnection] Initialize received id=1
[error] Failed to focus Codex view error="command 'workbench.view.extension.codexSecondaryViewContainer' not found"

Related existing reports (please do not close this as TRAE-only):

• #17290 — same container warning in Cursor, still open, little repro detail
• #15780 — identical focus error in another VS Code fork; a local patch forcing the non-secondary path was reported to work. Closed as "works in Cursor". That is no longer true on Cursor 3.15.6+.

What steps can reproduce the bug?

1. Install Cursor 3.15.6 or 3.15.19 (VS Code API 1.128.0).
2. Install/enable openai.chatgpt (Codex IDE extension) 26.803.x.
3. Reload the window.
4. Run Codex: Open Codex Sidebar.
5. Observe: no full Codex sidebar. Logs show codexSecondaryViewContainer missing and Failed to focus Codex view.
6. Run Codex: New Codex Agent. A new empty conversation tab opens without history.
7. Downgrade Cursor to 3.14.27 without changing the extension. Open Codex Sidebar works again, with session history.

Cursor reports vscode.version as 1.128.0. The extension treats >= 1.106 as "secondary sidebar is supported":

• package.json shows the Activity Bar container only when chatgpt.doesNotSupportSecondarySidebar
• the Secondary Side Bar container when !chatgpt.doesNotSupportSecondarySidebar
• Open Codex Sidebar then runs workbench.view.extension.${containerId} for codexSecondaryViewContainer

Cursor 3.15.6+ rejects third-party secondarySidebar view containers, so the extension hides the Activity Bar icon and then tries to focus a container that was never registered.

Claude Code still works independently because it always contributes a fallback Activity Bar container (claude-sessions-sidebar). Codex does not.

What is the expected behavior?

If the host does not actually provide a usable Secondary Side Bar container (Cursor 3.15.6+, and other forks like TRAE):

1. Set chatgpt.doesNotSupportSecondarySidebar (or equivalent) so the Activity Bar / codexViewContainer path is used.
2. Codex: Open Codex Sidebar should focus that fallback view.
3. The independent Codex UI should include session history / thread list / resume, not only New Codex Agent.

Detecting support via vscode.version >= 1.106 is not enough on Cursor: the host reports 1.128 but then refuses the contribution.

A capability check (does workbench.view.extension.codexSecondaryViewContainer exist after contribute, or does the host expose workbench.action.focusAuxiliaryBar and accept extension view containers there) would match the TRAE diagnosis in #15780.

Additional information

Cursor versions tested:

| Cursor | Codex independent sidebar with history |
|--------|------------------------------------------|
| 3.14.27 | Works |
| 3.15.6 / 3.15.19 | Broken (this issue) |

Cursor staff have said reserving the Secondary Side Bar for Cursor Agent is intentional. That is fine for this report. The bug is that Codex then has no working independent shell, while Claude Code in the same IDE still does.

I am currently staying on Cursor 3.14.27 solely so Codex remains usable.