Function release_session_slot 

fn release_session_slot(
    session_id: SessionId,
    session_data: SessionSlot,
    reason: ClosureReason,
)

Tears down a Session slot: stops its tasks and returns what it holds.

Logs nothing at INFO, because it also cleans up a Session whose setup failed before it was established (see SessionSlotGuard). An established Session is closed with close_session.