Things were working, suddenly regressed

SVSim.EmulatedEntrypoint/Models/Dtos/DefaultDeck.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos;
+
+/// <summary>
+/// One of the eight "starter" decks (one per class), as surfaced under
+/// <c>/deck/info data.default_deck_list</c>. Wire shape derived from 2026-05-23 prod capture.
+/// Used by the client both as new-account defaults and as the source for "use default deck".
+/// </summary>
+[MessagePackObject]
+public class DefaultDeck
+{
+    [JsonPropertyName("deck_no")]
+    [Key("deck_no")]
+    public int DeckNo { get; set; }
+
+    [JsonPropertyName("class_id")]
+    [Key("class_id")]
+    public int ClassId { get; set; }
+
+    [JsonPropertyName("sleeve_id")]
+    [Key("sleeve_id")]
+    public long SleeveId { get; set; }
+
+    [JsonPropertyName("leader_skin_id")]
+    [Key("leader_skin_id")]
+    public int LeaderSkinId { get; set; }
+
+    [JsonPropertyName("deck_name")]
+    [Key("deck_name")]
+    public string DeckName { get; set; } = string.Empty;
+
+    /// <summary>40 card_id values — same card may repeat (max 3 per card per Shadowverse rules).</summary>
+    [JsonPropertyName("card_id_array")]
+    [Key("card_id_array")]
+    public List<long> CardIdArray { get; set; } = new();
+}