MCP HTTP/SSE (Rube/Composio) fails to start with 'request timed out' on macOS (Codex 0.29.0) #3196

Title: MCP HTTP/SSE servers (Rube/Composio) fail to start with "request timed out" in Codex CLI on macOS

Summary

• Attempting to use the Rube (Composio) MCP hub via its MCP URL https://rube.app/mcp with Codex CLI.
• Direct transport = "http" + url = … in ~/.codex/config.toml is rejected (schema expects stdio command).
• Implemented stdio→HTTP/SSE proxy (first Deno, then Node 20) to bridge Codex to Rube. Codex still reports timeouts when starting the MCP client.
• Even after providing the signed token from Rube (Authorization or X-API-Key), Codex shows: MCP client for 'rube' failed to start: request timed out.

Steps to Reproduce

1. Add an MCP entry (stdio) that launches a small proxy which forwards to https://rube.app/mcp over Streamable HTTP with SSE fallback.

[mcp_servers.rube]
command = "/Users/danialhasan/.nvm/versions/node/v20.19.0/bin/node"
args = [
  "/Users/danialhasan/Desktop/dev.nosync/scripts/rube-proxy-node/index.mjs"
]
# Token redacted; header can be Authorization or X-API-Key depending on provider docs
env = { RUBE_URL = "https://rube.app/mcp", RUBE_TOKEN = "<redacted>", RUBE_AUTH_HEADER = "Authorization" }

2. Restart Codex CLI and open a session.
3. Observe error in TUI: 🖐 Failed to create MCP connection manager: request timed out (and/or MCP client for 'rube' failed to start: request timed out).
4. Proxy stderr with invalid token shows 401 from SSE; with token provided, Codex still times out at startup.

Expected

• Codex should support HTTP/Streamable HTTP/SSE MCP servers natively (e.g., transport = "http" with url and headers), or at least not time out when a stdio proxy is used.
• On auth/network errors from the remote MCP server, surface the HTTP status/message instead of a generic startup timeout.

Actual

• Codex fails to initialize the MCP connection with a generic timeout.
• No actionable error details are surfaced in the TUI; proxy logs show SSE/HTTP behavior but Codex reports only a timeout.

Environment

• macOS 15.2 (arm64)
• Codex CLI 0.29.0
• Node.js v20.19.0 for stdio proxy (also tried Deno 2.4.4)
• Deno and Node proxies both attempted; Node 20 used to avoid older Node fetch/stream incompatibilities

Additional Notes / Attempts

• Direct TOML with transport = "http" + url was rejected by Codex config parser (requires [mcp_servers.<name>] with command).
• Deno-based stdio proxy worked functionally but still resulted in request timed out from Codex.
• Node-based proxy (using @modelcontextprotocol/sdk 1.17.5) connects in background; still see Codex timeout on client start with valid token and header.

Related Issues

• Native SSE transport support for MCP servers #2129 Feature Request: Native SSE transport support for MCP servers
• SSE based MCP servers are non-configurable #2320 SSE based MCP servers are non-configurable
• feat: enable Streamable HTTP MCP servers & lazy loading of tools #2550 feat: enable Streamable HTTP MCP servers & lazy loading of tools
• Codex CLI on Windows 11: MCP server (Context7) fails with “request timed out” #2555 Windows 11: MCP server (Context7) fails with “request timed out”
• feat(mcp): per-server startup timeout #3182 feat(mcp): per-server timeout and capture server stdout/stderr
• Make MCP Request timeout configurable #2346 Make MCP Request timeout configurable

Request

• Add native support for HTTP/Streamable HTTP/SSE MCP servers in ~/.codex/config.toml (e.g., transport = "http", url, and headers).
• Improve error propagation so Codex surfaces HTTP status (401/403/405) and response body from remote MCP servers on startup.
• Document recommended auth header handling for HTTP MCP (Authorization vs X-API-Key) with examples.
• Consider a per-server configurable connect timeout and retry policy.

Happy to provide a minimal proxy repo or more logs if helpful.