milestone 26: upstream health answers for the selected period

admin/src/lib/format.ts

@@ -21,6 +21,24 @@ export function formatBytes(bytes: number): string {
 	return `${value.toFixed(1)} ${unit}`;
 }
 
+const AGE_UNITS = [
+	{ seconds: 86400, suffix: "d" },
+	{ seconds: 3600, suffix: "h" },
+	{ seconds: 60, suffix: "m" },
+] as const;
+
+/**
+ * Seconds of elapsed time → a coarse "3h ago". Truncating and single-unit on
+ * purpose: this labels a snapshot the caller renders once, so a reader must not
+ * take it for a live count. Nothing re-renders it as it ages.
+ */
+export function formatAge(seconds: number): string {
+	for (const unit of AGE_UNITS) {
+		if (seconds >= unit.seconds) return `${Math.floor(seconds / unit.seconds)}${unit.suffix} ago`;
+	}
+	return `${Math.floor(seconds)}s ago`;
+}
+
 /** Microseconds → milliseconds with one decimal, e.g. 1234 → "1.2 ms". */
 export function formatMicros(micros: number): string {
 	return `${(micros / 1000).toFixed(1)} ms`;