Bug: Magnific MCP OAuth flow fails — session state lost between authenticate and complete_authentication

Description

When using the Magnific MCP server (https://mcp.magnific.com/) via HTTP transport in Claude Code desktop app, the OAuth flow consistently fails with:

"No OAuth flow is in progress for magnific. Call mcp__magnific__authenticate first, then retry with the callback URL."

This happens even though authenticate was just called successfully moments before.

Steps to Reproduce

1. Add the server: claude mcp add --transport http magnific https://mcp.magnific.com/
2. Call mcp__magnific__authenticate → receive auth URL
3. Open the URL in the browser, complete OAuth login
4. Copy the callback URL (http://localhost:<port>/callback?code=...&state=...) from the browser address bar
5. Call mcp__magnific__complete_authentication with the callback URL

Expected Behavior

Authentication completes successfully and Magnific tools become available.

Actual Behavior

complete_authentication returns: "No OAuth flow is in progress for magnific."

Root Cause (suspected)

The MCP connection drops and reconnects between step 2 and step 5 (visible in the session as repeated "MCP server disconnected / reconnected" events). On reconnection, the OAuth session state is reset, so complete_authentication finds no active flow.

Tried 3+ times — same result every time. The issue appears to be a race condition between the MCP server's session lifecycle and the OAuth flow duration (the user needs a few seconds to log in and copy the callback URL).

Environment

• Claude Code v0.2.1
• macOS 15 (Mac Mini M4 Pro)
• Transport: HTTP (--transport http)
• MCP server: https://mcp.magnific.com/