feat(bp): /battle_pass/buy — crystal-cost + retroactive premium grants

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

SVSim.EmulatedEntrypoint/Models/Dtos/BattlePass/BattlePassAchievedInfoDto.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.BattlePass;
+
+/// <summary>
+/// achieved_info wrapper inside /battle_pass/buy response
+/// (Wizard/BattlePassBuyTask.cs:37-40).
+/// </summary>
+[MessagePackObject]
+public class BattlePassAchievedInfoDto
+{
+    [JsonPropertyName("battle_pass_reward_list")]
+    [Key("battle_pass_reward_list")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public List<BattlePassReceivedRewardDto> BattlePassRewardList { get; set; } = new();
+}

SVSim.EmulatedEntrypoint/Models/Dtos/BattlePass/BattlePassBuyRequest.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+using SVSim.EmulatedEntrypoint.Models.Dtos.Requests;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.BattlePass;
+
+/// <summary>
+/// /battle_pass/buy request (Wizard/BattlePassBuyTask.cs:8-13). Inherits viewer_id, steam_id,
+/// steam_session_ticket from BaseRequest. Per memory feedback_msgpack_request_dtos, the
+/// [MessagePackObject] + [Key] attrs are required even though integration tests post JSON.
+/// </summary>
+[MessagePackObject]
+public class BattlePassBuyRequest : BaseRequest
+{
+    [JsonPropertyName("season_id")]
+    [Key("season_id")]
+    public int SeasonId { get; set; }
+
+    [JsonPropertyName("id")]
+    [Key("id")]
+    public int Id { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/BattlePass/BattlePassBuyResponse.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.BattlePass;
+
+/// <summary>
+/// /battle_pass/buy response (Wizard/BattlePassBuyTask.cs:30-52). result_code carries the
+/// envelope failure path: 22 = insufficient crystals, 23 = already premium,
+/// 24 = outside BP period / season mismatch.
+/// </summary>
+[MessagePackObject]
+public class BattlePassBuyResponse
+{
+    [JsonPropertyName("result_code")]
+    [Key("result_code")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public int ResultCode { get; set; } = 1;
+
+    [JsonPropertyName("achieved_info")]
+    [Key("achieved_info")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public BattlePassAchievedInfoDto AchievedInfo { get; set; } = new();
+
+    [JsonPropertyName("reward_list")]
+    [Key("reward_list")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public List<BattlePassRewardListEntryDto> RewardList { get; set; } = new();
+}

SVSim.EmulatedEntrypoint/Models/Dtos/BattlePass/BattlePassReceivedRewardDto.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.BattlePass;
+
+/// <summary>
+/// One entry in /battle_pass/buy → achieved_info.battle_pass_reward_list[]
+/// (Wizard/BattlePassBuyTask.cs:42-48). Delta entries; numerics are int here, not string-typed.
+/// </summary>
+[MessagePackObject]
+public class BattlePassReceivedRewardDto
+{
+    [JsonPropertyName("reward_type")]
+    [Key("reward_type")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public int RewardType { get; set; }
+
+    [JsonPropertyName("reward_detail_id")]
+    [Key("reward_detail_id")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public long RewardDetailId { get; set; }
+
+    [JsonPropertyName("reward_number")]
+    [Key("reward_number")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public int RewardNumber { get; set; }
+}

SVSim.EmulatedEntrypoint/Models/Dtos/BattlePass/BattlePassRewardListEntryDto.cs

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+using MessagePack;
+using System.Text.Json.Serialization;
+
+namespace SVSim.EmulatedEntrypoint.Models.Dtos.BattlePass;
+
+/// <summary>
+/// One entry in /battle_pass/buy → reward_list[]. POST-STATE TOTALS for affected goods +
+/// currency, per memory project_wire_reward_list_post_state. Matches RewardListEntry shape
+/// used by /pack/open etc.
+/// </summary>
+[MessagePackObject]
+public class BattlePassRewardListEntryDto
+{
+    [JsonPropertyName("reward_type")]
+    [Key("reward_type")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public int RewardType { get; set; }
+
+    [JsonPropertyName("reward_id")]
+    [Key("reward_id")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public long RewardId { get; set; }
+
+    [JsonPropertyName("reward_num")]
+    [Key("reward_num")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.Never)]
+    public int RewardNum { get; set; }
+}