Codex cannot handshake with WebStorm MCP server (SSE endpoint), initialize fails

Summary

Codex Desktop cannot connect to the webstorm MCP server even though WebStorm MCP is running and reachable.
Handshake fails during initialize.

Environment

• Date: February 14, 2026
• OS: macOS
• IDE: WebStorm MCP Server 2025.3.2
• Codex config path: /Users/nookiegrey/.codex/config.toml
• MCP server config:
• [mcp_servers.webstorm]
• url = "http://127.0.0.1:64342/sse"

Steps to Reproduce

1. Start WebStorm with MCP server enabled on port 64342.
2. Configure Codex MCP server as:

• url = "http://127.0.0.1:64342/sse"

1. Call MCP API from Codex (for example list_mcp_resources for server webstorm).

Expected

Codex completes initialize handshake and can list resources/tools.

Actual

Codex fails during handshake with:
Unexpected content type: None, when send initialize request

Additional Diagnostics

• GET http://127.0.0.1:64342/sse returns 200 OK with text/event-stream.
• GET http://127.0.0.1:64342/mcp returns 404.
• POST /message?sessionId=... returns 202 Accepted.
• Direct MCP stdio initialize against WebStorm runner returns valid:
• serverInfo.name = "WebStorm MCP Server"
• serverInfo.version = "2025.3.2"

Suspected Cause

Codex appears to treat the configured URL as streamable HTTP transport, while WebStorm exposes SSE transport (/sse + /message?sessionId=...), leading to protocol mismatch at initialize.