Claude Code panel broken in Cursor 3.10.x — view container fails to mount, works on 3.9.16

Preflight Checklist

• [x] I have searched existing issues and this hasn't been reported yet
• [x] This is a single bug report (please file separate reports for different bugs)
• [x] I am using the latest version of Claude Code

What's Wrong?

Bug Description

After Cursor auto-updated to 3.10.11, the Claude Code extension's panel stopped
working. The extension activates, but its view container fails to mount and the
extension host repeatedly restarts. The Claude Code view falls back into the
Explorer container; the only working surface is an editor tab.

Logs show:

• View container 'claude-sidebar-secondary' does not exist
• Extension host restarting repeatedly during startup

This appears to share a root cause with #31375 (closed as stale, then locked):
the extension gates secondary-sidebar registration on parsing vscode.version,
which misfires on forks like Cursor that report their own version numbering
(3.10.11 here). A commenter there proposed capability detection (checking for
workbench.action.focusAuxiliaryBar / workbench.action.toggleAuxiliaryBar)
instead of version parsing, plus always registering the activity bar icon as a
fallback — never actioned before the thread was locked.

Steps to Reproduce

1. Install Claude Code extension in Cursor 3.10.11 (Windows x64, user setup)
2. Open any workspace; open the Claude Code panel
3. Panel view lands in the Explorer container / fails to mount properly
4. "View: Reset View Locations" + reload does not fix it; reinstalling the

extension does not fix it

Expected Behavior

Claude Code panel opens and docks reliably, as it does on Cursor 3.9.16.

Workaround

Downgrading Cursor to 3.9.16 fully restores correct behavior (update.mode set
to "none" to prevent silent re-upgrade).

Environment

• Editor: Cursor 3.10.11 (user setup), commit 4ef9fe3d055f8c4523179a090f14eb835bc3c940, Windows_NT x64 10.0.19045
• VS Code Extension API: 1.125.0
• Working version for comparison: Cursor 3.9.16
• Extension: anthropic.claude-code 2.1.202

What Should Happen?

The Claude Code panel opens and docks reliably in its own view container, as it does on Cursor 3.9.16.

Error Messages/Logs

View container 'claude-sidebar-secondary' does not exist
Extension host restarting repeatedly during startup

Steps to Reproduce

1. Install Claude Code extension 2.1.202 in Cursor 3.10.11 (Windows x64, user setup)
2. Open any workspace; open the Claude Code panel
3. Panel view lands in the Explorer container / fails to mount properly
4. "View: Reset View Locations" + reload does not fix it; reinstalling the extension does not fix it
5. Same extension on Cursor 3.9.16: works correctly

Claude Model

_No response_

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Extension unchanged (2.1.202) — regression is in host editor: Cursor 3.9.16 works, 3.10.11 broken

Claude Code Version

2.1.202 (VS Code extension)

Platform

Other

Operating System

Windows

Terminal/Shell

Cursor

Additional Information

Platform: "Other" = Claude Pro/Max subscription via the VS Code/Cursor
extension (not direct API).

On 3.10.11 the panel lands misplaced in the Explorer container.
Likely related to Cursor's Glass layout replacing the secondary sidebar
(ongoing since Cursor 2.7.0; see also locked issue #31375 for the proposed
capability-detection fix).