fix(management): purge terminal PendingSecuredWrites rows on the list sweep after a retention window (review 2026-10-21 08/G3)

src/ZB.MOM.WW.ScadaBridge.ManagementService/ManagementServiceOptionsValidator.cs

@@ -11,7 +11,8 @@ namespace ZB.MOM.WW.ScadaBridge.ManagementService;
 /// section fails fast at boot with a clear, key-naming message.
 /// <para>
 /// <see cref="ManagementServiceOptions.SecuredWritePendingTtl"/> is intentionally NOT required positive:
-/// a non-positive value legitimately disables server-side secured-write expiry.
+/// a non-positive value legitimately disables server-side secured-write expiry. The same holds for
+/// <see cref="ManagementServiceOptions.SecuredWriteTerminalRetention"/> (non-positive disables the terminal-row purge).
 /// </para>
 /// </summary>
 public sealed class ManagementServiceOptionsValidator : OptionsValidatorBase<ManagementServiceOptions>
@@ -26,5 +27,9 @@ public sealed class ManagementServiceOptionsValidator : OptionsValidatorBase<Man
         builder.RequireThat(options.LongRunningCommandTimeout > FlowDebug.FlowDebugRunner.ResponseGrace,
             $"ScadaBridge:ManagementService:LongRunningCommandTimeout must exceed the 5-second response grace " +
             $"(was {options.LongRunningCommandTimeout}); it is the Ask timeout for transport/deploy commands.");
+
+        builder.RequireThat(options.SecuredWriteTerminalPurgeInterval >= TimeSpan.Zero,
+            $"ScadaBridge:ManagementService:SecuredWriteTerminalPurgeInterval must not be negative " +
+            $"(was {options.SecuredWriteTerminalPurgeInterval}); zero purges on every Secured Writes list.");
     }
 }