Function utcDay

telemetry-worker/src/rollup.ts:40–42

(atMs: number)

/** UTC YYYY-MM-DD — the key every event, rollup and chart is bucketed on. */
export function utcDay(atMs: number): string {
  return new Date(atMs).toISOString().slice(0, 10);
}

/** Rejects both the wrong shape and impossible dates (`2026-02-31` round-trips as `2026-03-03`). */
export function isValidDay(day: string): boolean {