Constant SESSION_ID_PLACEHOLDER 

pub const SESSION_ID_PLACEHOLDER: &str = "<session-id>";

The literal segment a reported path carries in place of a real session id, in --explain-scope and session_start.effective_grants.

Substituted by the consumer, from session_start.session_id. Never expanded here, so the report --explain-scope prints before a session exists and the one the trace carries are identical.