fix(purge): short first tick on all three purge timers so daily-recycled nodes still purge

src/ZB.MOM.WW.ScadaBridge.Commons/Types/PurgeTimerSchedule.cs

@@ -0,0 +1,33 @@
+namespace ZB.MOM.WW.ScadaBridge.Commons.Types;
+
+/// <summary>
+/// Shared initial-delay rule for the central retention-purge singletons
+/// (Audit Log partition purge, Site Call Audit terminal purge, KPI History
+/// sample purge). All three run on a long (up to 24 h) interval; scheduling the
+/// FIRST tick after a full interval meant a node that recycles more often than
+/// the interval — e.g. a daily container restart against a 24 h cadence — would
+/// never actually purge (arch-review 04, S9).
+/// </summary>
+/// <remarks>
+/// Purges are idempotent, so an early first sweep is always safe. Taking
+/// <c>min(interval, <see cref="ShortFirstTick"/>)</c> guarantees the first purge
+/// runs within five minutes of startup while leaving the steady-state cadence —
+/// and the millisecond intervals the actor test suites use — unchanged.
+/// </remarks>
+public static class PurgeTimerSchedule
+{
+    /// <summary>
+    /// Upper bound on the delay before the first purge tick. Short enough that a
+    /// frequently-recycled node still purges, long enough not to add startup churn.
+    /// </summary>
+    public static readonly TimeSpan ShortFirstTick = TimeSpan.FromMinutes(5);
+
+    /// <summary>
+    /// The initial delay a purge timer should use for its first tick given its
+    /// steady-state <paramref name="interval"/>: the interval itself when it is
+    /// already shorter than <see cref="ShortFirstTick"/> (preserving fast test
+    /// cadences), otherwise capped at <see cref="ShortFirstTick"/>.
+    /// </summary>
+    public static TimeSpan InitialDelay(TimeSpan interval) =>
+        interval < ShortFirstTick ? interval : ShortFirstTick;
+}