Things were working, suddenly regressed

SVSim.EmulatedEntrypoint/Models/Dtos/MasterPointRankingPeriod.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos;
+
+/// <summary>
+/// Master Points season window. Client only reads end_time at /mypage/index
+/// (MyPageTask.cs:113-114) when _masterResetNextTime hasn't been set yet, but
+/// prod also emits id / period_num / necessary_score / begin_time — we mirror
+/// them so the wire shape matches.
+/// </summary>
+[MessagePackObject]
+public class MasterPointRankingPeriod
+{
+    [JsonPropertyName("id")]
+    [Key("id")]
+    public int Id { get; set; }
+
+    [JsonPropertyName("period_num")]
+    [Key("period_num")]
+    public int PeriodNum { get; set; }
+
+    [JsonPropertyName("necessary_score")]
+    [Key("necessary_score")]
+    public int NecessaryScore { get; set; }
+
+    /// <summary>ISO datetime.</summary>
+    [JsonPropertyName("begin_time")]
+    [Key("begin_time")]
+    public string BeginTime { get; set; } = string.Empty;
+
+    /// <summary>ISO datetime. Required — client calls DateTime.Parse on it.</summary>
+    [JsonPropertyName("end_time")]
+    [Key("end_time")]
+    public string EndTime { get; set; } = string.Empty;
+}