Update docs/specification/draft/basic/transports.mdx

Co-authored-by: Mike Kistler <mikekistler@microsoft.com>

Author: ZachGerman

docs/specification/draft/basic/transports.mdx

@@ -184,7 +184,7 @@ servers which want to establish stateful sessions:
      securely generated UUID, a JWT, or a cryptographic hash).
    - The session ID **MUST** only contain visible ASCII characters (ranging from 0x21 to
      0x7E).
-2. If an `Mcp-Session-Id` is returned by the server, clients using
+2. If an `Mcp-Session-Id` is returned by the server during initialization, clients using
    the Streamable HTTP transport **MUST** include it in the `Mcp-Session-Id` header on
    all of their subsequent HTTP requests meant for that session.
    - Servers that require a session ID **SHOULD** respond to requests without an