Find alarms that stopped receiving data

For every enabled alarm, when the metric series behind it last produced a datapoint.

Answers the one question an alarm's own state cannot: is it still watching anything? Under the default not_breaching policy an alarm whose metric stopped being emitted — a deleted workforce, a disabled trace filter, a renamed metric — sits at ok indefinitely and looks identical to one that is genuinely healthy.

stale marks silence lasting ten evaluation windows (minimum one hour), which is long enough that a quiet-but-live series won't trip it. A brand-new alarm reads as stale until its first datapoint, which is accurate: it cannot fire yet.

For a ratio alarm, last_datapoint_at is the older of the two series, since a period only yields a datapoint where both sides have one. A live numerator over a dead denominator is therefore reported as stale — every period resolves to a missing ratio, so the alarm is blind despite one of its series still flowing. denominator_last_datapoint_at tells you which side went quiet.

Covers the same alarms GET /orgs/{org_id}/alarms returns for you, so healthy and stale_count describe your visible subset — a project-scoped caller gets their project's blind spots, not the org's.