The identifier that was treated as a session
A long-running operation hands back an identifier so the client can come back for the result. Because the identifier is unguessable, the handler skips re-checking who is asking.
The protocol has no sessions. There was no handshake that established who this caller is and there is no per-connection state carrying it forward. What looks like a session is a string, and holding a string is not being someone.
Outside every boundary: Operation handle (an opaque string), MCP server (no sessions exist; FAILED: trusts the handle), MCP client, Another caller (holds the handle), an empty slot for the proves who is asking, an empty slot for the ties the handle to a subject Connections: MCP client calls proves who is asking (step 1) proves who is asking calls MCP server — checked here (step 2) Operation handle controls ties the handle to a subject — an argument ties the handle to a subject controls MCP server — whose handle is it (step 3) Another caller must NOT reach MCP server — not identity