milestone 27: diagnostics — operational failures land in one curated log, resolved history purgeable

admin/src/lib/format.ts

@@ -39,6 +39,18 @@ export function formatAge(seconds: number): string {
 	return `${Math.floor(seconds)}s ago`;
 }
 
+/**
+ * Seconds of elapsed time → a coarse "3h", the same single truncated unit as
+ * `formatAge` without the "ago". For a span the caller labels itself, as in
+ * "active for 3h". A negative span reads "0s": clock skew is not a duration.
+ */
+export function formatDuration(seconds: number): string {
+	for (const unit of AGE_UNITS) {
+		if (seconds >= unit.seconds) return `${Math.floor(seconds / unit.seconds)}${unit.suffix}`;
+	}
+	return `${Math.max(0, Math.floor(seconds))}s`;
+}
+
 /** Microseconds → milliseconds with one decimal, e.g. 1234 → "1.2 ms". */
 export function formatMicros(micros: number): string {
 	return `${(micros / 1000).toFixed(1)} ms`;