An API-sourced live search that reached search.list has spent 100 units (the client records them
before it reads the status), so it keeps its daily slot: refunding it let a bogus cursor spend the
shared budget without ever counting against the cap. A failure before the call still gives the slot
back.
Every refund is rationed too (5 an hour per user and list): a cursor is a free string, and a request
built to fail would otherwise scrape YouTube from the server without end.
The API source asks the budget again right before search.list, under one process lock with the
call: checked apart, searches sent together at the last 100 units all passed and all spent.