feat: always sync full 24 months horizon of contingents

src/Service/ContingentSnapshotReader.php

@@ -24,8 +24,9 @@ class ContingentSnapshotReader
     /**
      * How old the snapshot may get before we stop presenting it as current availability.
      *
-     * The near-term sync runs every 15 minutes during the day and hourly overnight, so this only
-     * trips when the scheduler is genuinely broken, never on the normal cadence.
+     * The sync runs every 15 minutes during the day and hourly overnight, so even the sparsest
+     * cadence leaves five missed runs of slack: this only trips when the scheduler is genuinely
+     * broken, never on the normal cadence.
      */
     private const string MAX_SNAPSHOT_AGE = '-6 hours';