Cloudflare MCP fails after OAuth: Failed to open SSE stream Not Found

Support Bug Reports
1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Official Cloudflare API MCP connects via Streamable HTTP and completes OAuth successfully, then immediately fails with:

Streamable HTTP error: Failed to open SSE stream: Not Found

After 5 consecutive HTTP 404 responses on the SSE GET, Cursor tombstones the transport and the server stays disconnected.

Same failure on 3.12.10 and after upgrading to 3.12.17.
The Cloudflare docs MCP endpoint works fine on the same machine.

Steps to Reproduce

  1. Add the official Cloudflare API MCP URL entry in mcp.json under mcpServers.cloudflare.url
  2. Restart Cursor and open MCP settings
  3. Click Connect / Authenticate for cloudflare
  4. Complete Cloudflare OAuth in the browser
  5. Return to Cursor
  6. Open Output, then MCP Logs for user-cloudflare

Result: OAuth tokens persist, Streamable HTTP connect succeeds, then SSE GET fails with 404 and the connection is tombstoned.

Expected Behavior

After OAuth, Cloudflare API MCP should stay connected and expose its tools. If the server does not support GET SSE, it should return 405 and Cursor should not treat 404 as fatal session termination.

Operating System

Windows 10/11

Version Information

Version: 3.12.17
VSCode Version: 1.128.0
Commit: 0fb762053c34788bb7760d5673f8a6d4c8589d50
Date: 2026-07-17T02:53:53.006Z
OS: Windows_NT x64 10.0.19045

Additional Information

Log:
Successfully connected to streamableHttp server
MCP OAuth tokens persisted
Client error: Streamable HTTP error: Failed to open SSE stream: Not Found
Tombstoning streamable HTTP transport after 5 consecutive session HTTP 404 responses
createClient completed connected=false

Official config only. No mcp-remote. No transport overrides.
I can add the exact MCP URL in a follow-up reply if needed (new-user 2-link limit).

Does this stop you from using Cursor

No - Cursor works, but with this issue

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