Add server-authoritative RZ Coin rewards

api/QuestionsApi/Models/CreditModels.cs

@@ -5,7 +5,7 @@ namespace QuestionsApi.Models;
 
 public static class CreditEconomy
 {
-    public const int RollingEarningLimit = 20;
+    public const int RollingEarningLimit = 30;
     public static readonly TimeSpan EarningWindow = TimeSpan.FromHours(24);
     public const string ExamTokenSku = "exam_token_1";
     public const string QBankResetTokenSku = "qbank_reset_1";
@@ -34,6 +34,9 @@ public static class CreditEconomy
 
     public static RzStoreProduct? FindProduct(string sku) =>
         Products.FirstOrDefault(value => value.Sku.Equals(sku, StringComparison.Ordinal));
+
+    public static int FirstCorrectAmount(int difficulty) => difficulty >= 5 ? 3 : difficulty >= 4 ? 2 : 1;
+    public static int ReviewAmount(bool delayedRecovery) => delayedRecovery ? 3 : 1;
 }
 
 public static class SlotMachineEconomy
@@ -92,6 +95,65 @@ public sealed class RzStoreProduct
 public sealed class CreditEvent
 {
     public string OperationId { get; set; } = "";
+    public int CoinAmount { get; set; } = 1;
+    public DateTime CreatedUtc { get; set; }
+}
+
+public static class CreditReasonCodes
+{
+    public const string FirstCorrect = "qbank_first_correct";
+    public const string DifficultCorrect = "qbank_difficult_correct";
+    public const string ScheduledReview = "scheduled_review_correct";
+    public const string DelayedRecovery = "delayed_recovery";
+    public const string MasteryPracticing = "mastery_practicing";
+    public const string MasteryStrong = "mastery_strong";
+    public const string MasteryMastered = "mastery_mastered";
+    public const string ExamSimulationComplete = "exam_simulation_complete";
+    public const string Purchase = "purchase";
+}
+
+public sealed class CreditLedgerEntry
+{
+    [BsonId]
+    public string Id { get; set; } = "";
+    public string UserId { get; set; } = "";
+    public string OperationId { get; set; } = "";
+    public int RequestedAmount { get; set; }
+    public int Amount { get; set; }
+    public string ReasonCode { get; set; } = "";
+    public string Description { get; set; } = "";
+    public string SourceType { get; set; } = "";
+    public string SourceId { get; set; } = "";
+    public bool SubjectToRollingCap { get; set; }
+    public string State { get; set; } = "pending";
+    public DateTime CreatedUtc { get; set; }
+    public DateTime? AppliedUtc { get; set; }
+}
+
+public sealed class CreditAward
+{
+    public int Amount { get; set; }
+    public string ReasonCode { get; set; } = "";
+    public string Description { get; set; } = "";
+}
+
+public sealed class CreditAwardResult
+{
+    public CreditAward? Award { get; set; }
+    public CreditStatusResponse Status { get; set; } = new();
+}
+
+public sealed class CreditLedgerPage
+{
+    public List<CreditLedgerEntryResponse> Items { get; set; } = [];
+    public DateTime? NextBefore { get; set; }
+}
+
+public sealed class CreditLedgerEntryResponse
+{
+    public int Amount { get; set; }
+    public string ReasonCode { get; set; } = "";
+    public string Description { get; set; } = "";
     public DateTime CreatedUtc { get; set; }
 }
 
@@ -122,6 +184,7 @@ public sealed class UserCreditAccount
     public int QBankResetTokens { get; set; }
     public int BankCycle { get; set; }
     public bool InitialExamGrantApplied { get; set; }
+    public bool MasteryAwardBaselineApplied { get; set; }
     public List<CreditEvent> RecentEarnings { get; set; } = [];
     public List<CreditPurchaseEvent> Purchases { get; set; } = [];
     public List<SpinEvent> Spins { get; set; } = [];
@@ -142,6 +205,15 @@ public sealed class CreditStatusResponse
     public IReadOnlyList<RzStoreProduct> Products { get; set; } = CreditEconomy.Products;
 }
 
+public sealed record CreditAwardRequest(
+    string OperationId,
+    int Amount,
+    string ReasonCode,
+    string Description,
+    string SourceType,
+    string SourceId,
+    bool SubjectToRollingCap = true);
+
 public sealed class CreditPurchaseRequest
 {
     public string Sku { get; set; } = "";

api/QuestionsApi/Models/ExamSimulation.cs

@@ -117,6 +117,8 @@ public class ExamSimulationStateResponse
     public Dictionary<string, int> BlueprintTargets { get; set; } = [];
     public Dictionary<string, int> BlueprintActual { get; set; } = [];
     public List<QuestionResponse> ReviewQuestions { get; set; } = [];
+    public CreditStatusResponse? Credits { get; set; }
+    public List<CreditAward> CreditAwards { get; set; } = [];
 }
 
 public class ExamSimulationReadinessResponse

api/QuestionsApi/Models/QuestionResponse.cs

@@ -146,6 +146,7 @@ public class FirstQuestionAttemptResponse
     public int QuestionElo { get; set; } = 1000;
     public RatingChangeResponse? Rating { get; set; }
     public CreditStatusResponse? Credits { get; set; }
+    public List<CreditAward> CreditAwards { get; set; } = [];
 }
 
 public class SkipQuestionResponse

api/QuestionsApi/Models/ReviewQueueModels.cs

@@ -81,6 +81,8 @@ public sealed class ReviewQueueAttemptResponse
     public bool IsCorrect { get; set; }
     public string QueueState { get; set; } = ReviewQueueStates.Pending;
     public int PendingCount { get; set; }
+    public CreditStatusResponse? Credits { get; set; }
+    public List<CreditAward> CreditAwards { get; set; } = [];
 }
 
 public sealed class ReviewQueueRecordResult