docs(schedule): document recurring gate exhaustion

packages/schedule/tool-schedule/src/domain.ts

@@ -38,7 +38,11 @@ const LOCAL_TIME = /^(?<hour>\d{2}):(?<minute>\d{2}):(?<second>\d{2})(?:\.(?<fra
 const IANA_ZONE = /^[A-Za-z][A-Za-z0-9_+.-]*(?:\/[A-Za-z0-9_+.-]+)+$/
 const OFFSET_NAME = /^GMT(?:(?<sign>[+-])(?<hour>\d{2}):(?<minute>\d{2})(?::(?<second>\d{2}))?)?$/
 
-/** Whether the durable recurring gate has no four-digit-year admission left. */
+/**
+ * Whether the durable recurring gate has no four-digit-year admission left.
+ * @param lastAcceptedAt - Latest accepted recurring batch, when any.
+ * @returns `true` only when another compliant batch time is unrepresentable.
+ */
 export function isRecurringGateExhausted(lastAcceptedAt: string | undefined): boolean {
   return lastAcceptedAt !== undefined
     && Date.parse(lastAcceptedAt) + MIN_RECURRING_INTERVAL_SECONDS * 1_000 > MAX_FOUR_DIGIT_YEAR_MS