No access to mcp-session-id with get_http_headers(include_all=True)

[MrOdin0]

In my current application i want to use the mcp_session_id when i log my tool calls.
According to the discussion Is there any way to get session_id in middleware or @mcp.tools()? #940 it should be in the header.
But the headers returned in get_http_headers(include_all=True) do not contain the session id.

mcp = FastMCP("DemoServer")

class LoggingMiddleware(Middleware):

    async def on_call_tool (self, context: MiddlewareContext, call_next):
        headers = get_http_headers(include_all=True)
        print(f"middleware-headers: {headers}")
        result = await call_next(context)
        return result



@mcp.tool()
def demotool():
    """JUST A DEMO"""
    headers = get_http_headers(include_all=True)
    print(f"tool-headers: {headers}")
    return True

mcp.add_middleware(LoggingMiddleware())

if __name__ == "__main__":
    print("starting mcp")
    mcp.run(transport="http", host="0.0.0.0", port=8122)

I tested it both with Postman and a custom testing client, and both times many headers are omitted.

middleware-headers: {'accept': 'application/json,text/event-stream', 'content-type': 'application/json', 'user-agent': 'PostmanRuntime/7.44.1', 'postman-token': '95441dcb-400f-4252-8f70-a17c0dec517c', 'host': 'localhost:8122', 'accept-encoding': 'gzip, deflate, br', 'connection': 'keep-alive', 'content-length': '391'}
tool-headers: {'accept': 'application/json,text/event-stream', 'content-type': 'application/json', 'user-agent': 'PostmanRuntime/7.44.1', 'postman-token': '95441dcb-400f-4252-8f70-a17c0dec517c', 'host': 'localhost:8122', 'accept-encoding': 'gzip, deflate, br', 'connection': 'keep-alive', 'content-length': '391'}

middleware-headers: {'accept': 'application/json,text/event-stream', 'content-type': 'application/json', 'user-agent': 'axios/1.11.0', 'content-length': '259', 'accept-encoding': 'gzip, compress, deflate, br', 'host': 'localhost:8122', 'connection': 'keep-alive'}
tool-headers: {'accept': 'application/json,text/event-stream', 'content-type': 'application/json', 'user-agent': 'axios/1.11.0', 'content-length': '259', 'accept-encoding': 'gzip, compress, deflate, br', 'host': 'localhost:8122', 'connection': 'keep-alive'}

The header is set and properly initialized, because the tool call works correctly, and stops working if i change to an invalid session-id.
Am I missing something? Or is this the wanted behavior and there is no way to access the token from the server at runtime?

[hopeful0]

see #956 and #1242. Note that the fix not yet released.