HTTP MCP transport fails to connect to Cypress Cloud MCP server (missing Accept header)

Bug Description

Claude Code's HTTP MCP transport fails to connect to the Cypress Cloud MCP server at https://mcp.cypress.io/mcp, despite the server being reachable and the auth token being valid.

Environment

• Claude Code version: 2.1.79
• Platform: macOS (Darwin 25.3.0)
• Shell: zsh

MCP Server Configuration

{
  "CypressCloud": {
    "type": "http",
    "url": "https://mcp.cypress.io/mcp",
    "headers": {
      "Authorization": "Bearer <redacted>"
    }
  }
}

Also tried with "type": "sse" — same result.

Symptoms

• claude mcp list consistently shows: CypressCloud: https://mcp.cypress.io/mcp (HTTP) - ✗ Failed to connect
• Server never becomes available after multiple restarts
• No detailed error message is provided

Root Cause (Diagnosed)

The Cypress Cloud MCP server requires the client to send Accept: application/json, text/event-stream in the request headers. Without this, it returns:

{"jsonrpc":"2.0","error":{"code":-32000,"message":"Not Acceptable: Client must accept both application/json and text/event-stream"},"id":null}

A manual curl request with the correct Accept header succeeds:

curl -s \
  -H "Authorization: Bearer <token>" \
  -H "Accept: application/json, text/event-stream" \
  -H "Content-Type: application/json" \
  -X POST \
  -d '{"jsonrpc":"2.0","method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"claude-code","version":"1.0"}},"id":1}' \
  https://mcp.cypress.io/mcp

Returns a valid MCP initialize response with server capabilities.

Expected Behavior

Claude Code's HTTP transport should include Accept: application/json, text/event-stream in MCP protocol requests, as required by the Streamable HTTP transport spec (MCP spec reference).

Steps to Reproduce

1. Add the Cypress Cloud MCP server: claude mcp add --transport http --header "Authorization: Bearer <token>" -s local CypressCloud https://mcp.cypress.io/mcp
2. Restart Claude Code
3. Run claude mcp list — shows ✗ Failed to connect

Cypress Cloud MCP Docs

Setup instructions: https://docs.cypress.io/cloud/integrations/cloud-mcp