The Codex extension (26.5803.61601) installs and activates successfully, but its interface cannot be opened in Cursor 3.15.6.
Cursor rejects the extension’s Secondary Side Bar container because it is reserved for Cursor’s Agent UI. The logs then report that codexSecondaryViewContainer does not exist, followed by Failed to focus Codex view.
The same Codex extension version works correctly after downgrading Cursor to 3.14.27, indicating a compatibility regression in Cursor 3.15.6.
Steps to Reproduce
Install Cursor 3.15.6.
Install the Codex extension (openai.chatgpt, version 26.5803.61601).
Restart or reload Cursor.
Click the Codex icon or run the Open Codex Sidebar command.
Observe that the Codex interface does not open.
Downgrade Cursor to 3.14.27 without changing the Codex extension version.
Open Codex again and observe that it works.
Expected Behavior
View containers cannot be contributed to the Secondary Side Bar in Cursor.
It is reserved for Cursor’s agent UI.
View container ‘codexSecondaryViewContainer’ does not exist.
Failed to focus Codex view:
command ‘workbench.view.extension.codexSecondaryViewContainer’ not found
Hi @qxxq Thanks for the post. This is expected behavior rather than something that went wrong in 3.15.6.
The Secondary Side Bar (the right-hand panel where Cursor’s Agent tabs live) is reserved for Cursor’s own agent UI, so extensions can’t register a view container there. The first message in your logs is that rejection, and the two that follow about codexSecondaryViewContainer are downstream of it rather than separate problems.
Your 3.14.27 observation is accurate, and I want to be transparent about it. For roughly a month, a change on our side made that docking possible when it wasn’t meant to be, and 3.15.6 brings it back in line. The layout you had really did exist, and it wasn’t anything you configured. There’s no setting that restores it, and downgrading isn’t a lasting workaround, since 3.14 builds cut after that point carry the same behavior.
Codex still works, just not in that panel:
Left Activity Bar: if the view landed nested under Explorer, drag its section header onto the Activity Bar so it gets its own top-level icon. View: Reset View Locations followed by Developer: Reload Window can help if it’s stuck.
As an editor tab: run Codex: New Codex Agent from the Command Palette, then View: Split Editor Right for a side-by-side layout next to your code.
View: Reset View Locations followed by Developer: Reload Windowdoes not help.
I can open a new codex window via Codex: New Codex Agent but there is no access to all my previous codex sessions.
Your last update makes using Codex in Cursor completely unusable. Is it intentionally?
They used your subscription money to pay their team to remove the feature a significant portion of their users want. It wasn’t broken, it didn’t need to be changed or removed, but the Cursor team still chose to remove it because they don’t want people using Claude. It’s a terrible look from a customer perspective and makes us hesitant to keep using Cursor
Same, Codex extension became completely unusable in Cursor, it might be intentionally blocked even if it’s supposed to be a separate extension? Were you able to find a workaround?
Thankfully Codex desktop for Linux is finally available since very recently, that was the major reason I was using an extension inside Cursor before it came out