Hosted Claude Code: OAuth flow for n8n MCP never completes token handshake

Description

When using the hosted version of Claude Code (claude.ai/code, not the local CLI), the OAuth authentication flow for an n8n MCP server never completes the round-trip back to the session.

Steps to Reproduce

1. Configure an n8n MCP server via claude.ai integration settings

• URL: https://<instance>.app.n8n.cloud/mcp-server/http
• Config location: claude.ai

1. Run /mcp in Claude Code → select the n8n server → select "Authenticate"
2. Browser tab opens with the n8n OAuth consent screen
3. Complete authentication successfully in the browser (confirmed working)
4. Return to Claude Code

Expected Behavior

Claude Code should detect the completed OAuth flow and show the n8n MCP server as authenticated, with its tools available.

Actual Behavior

• Claude Code still shows Status: ⚠ needs authentication
• The /mcp dialog only offers "Authenticate" or "Disable" — no way to proceed
• Calling the authenticate tool programmatically returns: "Ask the user to run /mcp and select 'claude.ai n8n' to authenticate."
• Repeating the flow produces the same result — the token never persists to the session
• Only option is to press Escape to dismiss the dialog

Environment

• Claude Code version: Hosted (claude.ai/code web app)
• MCP server: n8n cloud instance via HTTP transport
• Browser: OAuth completes successfully (confirmed on n8n side)
• OS: macOS

Workaround

Setting up n8n as a local MCP server with direct HTTP transport bypasses the claude.ai OAuth proxy and works.

Notes

This appears to be specific to the hosted version's OAuth callback mechanism — the browser-side auth succeeds but the token is never propagated back to the Claude Code session.