Things were working, suddenly regressed

SVSim.EmulatedEntrypoint/Program.cs

@@ -7,6 +7,7 @@ using SVSim.Database.Repositories.Collectibles;
 using SVSim.Database.Repositories.Deck;
 using SVSim.Database.Repositories.Globals;
 using SVSim.Database.Repositories.Viewer;
+using SVSim.EmulatedEntrypoint.Extensions;
 using SVSim.EmulatedEntrypoint.Middlewares;
 using SVSim.EmulatedEntrypoint.Security.SteamSessionAuthentication;
 using SVSim.EmulatedEntrypoint.Services;
@@ -34,6 +35,9 @@ public class Program
             // value without a null guard. Emitting `"key":null` makes Contains return true and
             // crashes the client. Drop nulls during serialization so missing == absent.
             opt.JsonSerializerOptions.DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull;
+            // Format-typed properties serialize to/from the wire deck_format int via the
+            // client's FormatConvertApi mapping. See FormatExtensions.cs.
+            opt.JsonSerializerOptions.Converters.Add(new FormatJsonConverter());
         });
         // Learn more about configuring Swagger/OpenAPI at https://aka.ms/aspnetcore/swashbuckle
         builder.Services.AddEndpointsApiExplorer();