[BUG] Extensions Fail to Load/Install After Update to 1.21459.0

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?

After updating Claude Desktop to build 1.21459.0, three issues appeared immediately with no other changes made:

1. Fantastical extension broken - Was installed and functioning normally for 12 weeks prior. Immediately after the update, started receiving multiple error messages referencing Fantastical. No changes were made to the extension, its config, or system permissions.

1. Extensions page won't load - Navigating to Settings → Extensions shows "Loading extensions..." indefinitely. The spinner never resolves, no content loads, and no error is shown.

1. Browse Connectors/Extensions page broken install button - In Customize → Browse Connectors/Extensions, Fantastical shows as uninstalled. The Install button is replaced by a grey-and-black icon instead of a functioning button. Clicking produces no install action and no error message.

What Should Happen?

• Extensions page should load the list of installed/available extensions without hanging
• Fantastical, which was previously working for 12 weeks, should either still work or show a clear error/reinstall path
• The Install button should be clickable and either install the extension or show a specific error message

Error Messages/Logs

Multiple error messages referencing Fantastical appear after updating to build 1.21459.0. Specific error text was not captured in the report, but errors begin immediately on launch after the update. Extensions page shows no error — it simply hangs on "Loading extensions..." with a spinner indefinitely.

Steps to Reproduce

1. Have Fantastical extension installed and working in Claude Desktop (was working for 12 weeks)
2. Update Claude Desktop to build 1.21459.0 (f7518f, built 2026-07-14T05:32:17.000Z)
3. Relaunch Claude Desktop
4. Observe multiple error messages referencing Fantastical on startup
5. Navigate to Settings → Extensions
6. Observe the Extensions page hangs on "Loading extensions..." indefinitely with a spinner — no content loads
7. Navigate to Customize → Browse Connectors/Extensions
8. Observe Fantastical shows as uninstalled with a non-functional grey-and-black icon in place of the Install button
9. Click the icon — no action occurs, no error message shown

Troubleshooting already attempted:

• Quit and reopened Claude Desktop completely → no change
• Cleared cache → no change
• Restarted system → no change

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

The version prior to 1.21459.0 (exact version number not captured; extension worked for 12 weeks before this update)

Claude Code Version

1.21459.0 (f7518f, built 2026-07-14T05:32:17.000Z)

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Terminal.app (macOS)

Additional Information

Environment:

• Claude Desktop version: 1.21459.0 (f7518f), built 2026-07-14T05:32:17.000Z
• OS: macOS Tahoe 26, Version 26.5.2 (25F84)
• Affected extension: Fantastical Connector (previously installed and working without issue for 12 weeks prior to this update)
• Full Disk Access and other permissions were not changed during this period

Requested Fix:

• Confirm whether 1.21459.0 has a known regression affecting extension loading/installation
• Provide a way to roll back to the prior working build if no immediate fix is available

Note: This issue is with Claude Desktop's Extensions system, not Claude Code itself. Filing here as directed by the support/bug report process.