[BUG] Claude Desktop (macOS, latest): installing ANY custom `.mcpb` connector breaks the whole Extensions UI — icons vanish, per-connector config won't open, install/toggle buttons dead — until app rollback

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?

On the current macOS build, the Extensions/Connectors UI is healthy only while no custom (developer/.mcpb) connector is installed. The moment any custom connector is installed, the extensions UI breaks app‑wide and stays broken:

• All connector icons disappear (blank across every connector, not just the new one).
• The per‑connector configuration panel can no longer be opened for any custom connector.
• Action controls render as blank grey placeholders and are unclickable — e.g. the Install button on the .mcpb preview dialog, and the enable/config controls on a connector's detail page.

This is not specific to one bundle. It reproduces with multiple different connectors, regardless of zip compression (both DEFLATE mcpb pack bundles and STORED/zip -0 bundles trigger it) and regardless of server language (Node and Python/uv connectors both trigger it). Manually removing the connector's unpacked folder and its entry in extensions-installations.json (with the app quit) does not restore the UI. The only thing that restores it is rolling Claude Desktop back to the previous version.

A clean‑slate test isolates it cleanly: quit the app, rename ~/Library/Application Support/Claude/Claude Extensions/ and extensions-installations.json aside, relaunch → the extensions UI is fully healthy with zero extensions. Install any one custom connector → it breaks again immediately.

What Should Happen?

Installing a custom connector should not break the Extensions UI. Icons, the per‑connector configuration panel, and the install/enable controls should keep working.

Error Messages/Logs

The only error emitted around the breakage (from a Python/uv‑based connector) is the `disclaimer` helper failing to spawn python:


[error] Failed to read version of python binary "python", failed with Error: Failed to spawn python (via disclaimer): /Applications/Claude.app/Contents/Helpers/disclaimer exited with code 127: Failed to spawn process: No such file or directory


Removing that Python connector cleared this log line, but the UI stayed broken — so the crash is triggered by installing/loading a custom connector in general, not by the python lookup specifically.

Steps to Reproduce

1. Quit Claude Desktop; rename ~/Library/Application Support/Claude/Claude Extensions/ + extensions-installations.json aside; relaunch → Extensions UI healthy, zero extensions.
2. Install any one custom .mcpb connector (Directory install or a local .mcpb).
3. Observe: connector icons vanish app‑wide, the per‑connector configuration panel won't open, and install/toggle buttons render as unclickable grey placeholders.
4. Removing the connector's files + extensions-installations.json entry (app quit) does not restore the UI.
5. Roll Claude Desktop back to the previous version → UI restored, custom connectors work again.

Claude Model

None

Is this a regression?

Yes, this worked in a previous version

Last Working Version

Claude 1.20186.9 (69f150) 2026-07-14T05:52:31.000Z

Claude Code Version

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

Platform

Anthropic API

Operating System

macOS

Terminal/Shell

Other

Additional Information

Same build/regression cluster, but each describes a different failure mode than the app‑wide UI breakage above:

• #68484 — Directory extension installs silently fail on macOS (same disclaimer python code‑127 error, build 1.12603.1)
• #67919 — uninstalled extension can't be reinstalled (install hangs / no‑op), state survives app reinstall
• #68316 — macOS Claude Desktop becomes corrupted/frozen, requires full Reset App
• #61661 — Customize → Plugins panel greyed/uninteractive; enabled plugins disappear
• #31864 — auto‑update silent MCP extension conflict (Windows)

Workarounds found: (a) roll back to the previous Claude Desktop version; (b) to keep the app usable meanwhile, remove all custom connectors via the clean‑slate rename above.