Every recorded save of the cost control, plus changes to the alert linked to it (marked LINKED_ALERT), with who saved it, when, and each setting's before and after. A budget's history lists changes of alerts linked to it now or at any recorded revision, because hiding a formerly linked alert's changes would hide part of the trail. Newest first; the sort parameter is ignored. revision is an opaque ordering key shared by items saved in one request. Authors are masked: a Revenium staff member shows as Revenium Support, a change made by the system or recorded when change history began shows as Revenium (system), and an API key shows its name and owner. A deleted item's history stays readable. An unknown, malformed or unreadable id answers 404.