fix(configdb): opt-in config-audit retention purge + after-state size cap (review 2026-10-21 08/G1)

src/ZB.MOM.WW.ScadaBridge.ConfigurationDatabase/Services/AuditService.cs

@@ -23,6 +23,15 @@ public class AuditService : IAuditService
         MaxDepth = 32
     };
 
+    /// <summary>
+    /// Upper bound (characters) on a serialized <c>AfterStateJson</c>. A larger payload (e.g. a
+    /// whole template graph with every script body) is replaced by a small truncation marker so
+    /// one audit row can never grow without bound. Valid JSON is preserved either way.
+    /// </summary>
+    public const int MaxAfterStateChars = 256 * 1024;
+
+    private const int TruncatedPreviewChars = 4 * 1024;
+
     /// <summary>
     /// Initializes the audit service with the EF Core context and correlation context.
     /// </summary>
@@ -72,7 +81,17 @@ public class AuditService : IAuditService
     {
         try
         {
-            return JsonSerializer.Serialize(afterState, AuditSerializerOptions);
+            var json = JsonSerializer.Serialize(afterState, AuditSerializerOptions);
+            if (json.Length <= MaxAfterStateChars)
+                return json;
+
+            return JsonSerializer.Serialize(new
+            {
+                AuditTruncated = true,
+                OriginalLength = json.Length,
+                StateType = afterState.GetType().FullName,
+                Preview = json[..TruncatedPreviewChars]
+            });
         }
         catch (Exception ex) when (ex is JsonException or NotSupportedException)
         {