Windows Desktop App: Remote MCP OAuth callback not completing (tools show 'Not connected' after successful authorization)

Summary

On the Windows Desktop App (Claude Code), Remote MCP OAuth authorization appears to complete successfully (UI shows "connected"), but the tools remain unusable with a "Not connected" error. The same Remote MCP server works correctly when using Claude Code from the terminal (CLI).

Environment

• OS: Windows 11 Home 10.0.26200
• Claude Code: Desktop App (Windows)
• Remote MCP Server: freee-mcp (https://mcp.freee.co.jp/mcp)

Steps to Reproduce

1. Open Claude Code Desktop App on Windows
2. Add a custom connector (Remote MCP): URL = https://mcp.freee.co.jp/mcp
3. Browser opens with OAuth authorization page (freee login + "許可する" / "Authorize" button)
4. Click "Authorize" — UI shows connection as successful
5. Try to use any MCP tool (e.g., freee_get_current_company)

Expected Behavior

Tools should work after authorization is completed.

Actual Behavior

• All MCP tools return "Not connected" error
• claude mcp list from CLI shows "Needs authentication"
• The same MCP server works perfectly when running claude from a terminal (OAuth flow completes correctly and tools are functional)

Additional Context

• The Remote MCP connection was originally working from the Desktop App
• After disconnecting and reconnecting, the OAuth callback appears to not reach the Desktop App properly
• The authorization completes on the server side (freee shows the app as authorized), but the token doesn't get back to the Desktop App
• Terminal CLI sessions authenticate correctly with the same MCP server and URL
• Restarting the Desktop App multiple times did not resolve the issue