Python MCP SDK's session.initialize() only returns the parsed JSON-RPC result, not the HTTP response headers (MCP-Session-Id)

[neerajagarwal041]

Ee're injecting MCP-Session-Id in the middleware is in the HTTP response headers at MCP Server, but the MCP SDK's session.initialize() only returns the parsed JSON-RPC result, not the HTTP headers.

The middleware IS adding the header to the HTTP response (both for the initial SSE GET and for the subsequent POST requests to /messages/), but the MCP SDK doesn't expose those headers to us.

Our MCP Server using the mcp.server.fastmcp Python SDK.

[SamMorrowDrums]

I believe this was opened in the GitHub MCP Server by mistake, as it sounds like it is about your server and the Python SDK handling headers internally, so I'd recommend opening an issue there:

https://github.com/jlowin/fastmcp