Desktop app: API Error 400 - input_schema does not support oneOf/allOf/anyOf (tools.23)

Description

Claude Code Desktop version fails to start a conversation with the following API error:

API Error: 400 {"type":"error","error":{"type":"invalid_request_error","message":"tools.23.custom.input_schema: input_schema does not support oneOf, allOf, or anyOf at the top level"},"request_id":"req_011CZQavrcD9PuZuB5iteBaE"}

Environment

• Platform: Windows 11 Home 10.0.26200
• CLI version: 2.1.83 (works fine)
• Desktop version: latest available
• Plugins enabled: discord@claude-plugins-official (v0.0.4), claude-mem (v10.3.1)

Investigation

• Verified all plugin MCP tool schemas (Discord, claude-mem) — none use oneOf/allOf/anyOf at the top level of inputSchema
• CLI version works without issues with the same configuration
• The issue appears to be in one of the built-in tools (index 23, 0-based) that the desktop app registers with the API

Steps to reproduce

1. Open Claude Code Desktop on Windows 11
2. Start a new conversation
3. Error appears immediately

Expected behavior

The desktop app should work the same as the CLI version.