feat(ai): centralize durable usage

Add a content-free usage ledger with legacy backfill. Reserve Workspace and durable Strategy/CV work before execution so deleted history or duplicate admission cannot reset limits.

JobTrackerApi/Services/UserOperationStore.cs

@@ -13,7 +13,9 @@ public sealed record CreateUserOperation(
     string? SubjectId = null,
     int Priority = 0,
     int MaxAttempts = 3,
-    DateTime? DeadlineAtUtc = null);
+    DateTime? DeadlineAtUtc = null,
+    int UsageInputCharacters = 0,
+    int UsageReservedTokens = 0);
 
 public sealed record UserOperationCreation(UserOperation Operation, bool Created);
 public sealed record UserOperationLease(Guid OperationId, string OwnerUserId, string LeaseToken, string TaskType, string PrivacyPolicy, string? SubjectType, string? SubjectId, int AttemptCount, DateTime? DeadlineAtUtc);
@@ -73,6 +75,18 @@ public sealed class UserOperationStore(JobTrackerContext db, TimeProvider timePr
             DeadlineAtUtc = request.DeadlineAtUtc,
         };
         db.UserOperations.Add(operation);
+        AiUsageRecord? usage = null;
+        if (request.UsageReservedTokens > 0)
+        {
+            usage = AiUsageMeter.NewOperationRecord(
+                owner,
+                operation.Id,
+                operation.TaskType,
+                request.UsageInputCharacters,
+                request.UsageReservedTokens,
+                new DateTimeOffset(now));
+            db.AiUsageRecords.Add(usage);
+        }
         try
         {
             await db.SaveChangesAsync(cancellationToken);
@@ -81,6 +95,7 @@ public sealed class UserOperationStore(JobTrackerContext db, TimeProvider timePr
         catch (DbUpdateException)
         {
             db.Entry(operation).State = EntityState.Detached;
+            if (usage is not null) db.Entry(usage).State = EntityState.Detached;
             existing = await db.UserOperations.FirstOrDefaultAsync(
                 item => item.TaskType == request.TaskType && item.IdempotencyKey == request.IdempotencyKey,
                 cancellationToken);
@@ -170,6 +185,18 @@ public sealed class UserOperationStore(JobTrackerContext db, TimeProvider timePr
         string? model,
         string? completionStage,
         CancellationToken cancellationToken)
+        => await CompleteAsync(operationId, leaseToken, resultReference, provider, model, completionStage, null, null, cancellationToken);
+
+    public async Task<int> CompleteAsync(
+        Guid operationId,
+        string leaseToken,
+        string? resultReference,
+        string? provider,
+        string? model,
+        string? completionStage,
+        int? usageInputCharacters,
+        int? usageOutputCharacters,
+        CancellationToken cancellationToken)
     {
         EnsureOwnerScope();
         ValidateOptional(resultReference, 256, nameof(resultReference));
@@ -196,6 +223,15 @@ public sealed class UserOperationStore(JobTrackerContext db, TimeProvider timePr
                 cancellationToken);
         if (affected == 1)
         {
+            if (usageInputCharacters is not null && usageOutputCharacters is not null)
+            {
+                var estimatedTokens = (usageInputCharacters.Value + usageOutputCharacters.Value + 3) / 4;
+                await db.AiUsageRecords.Where(item => item.SourceType == "operation" && item.SourceId == operationId.ToString("D"))
+                    .ExecuteUpdateAsync(setters => setters
+                        .SetProperty(item => item.InputCharacterCount, usageInputCharacters.Value)
+                        .SetProperty(item => item.OutputCharacterCount, usageOutputCharacters.Value)
+                        .SetProperty(item => item.EstimatedTokenCount, estimatedTokens), cancellationToken);
+            }
             db.UserNotifications.Add(CreateTerminalNotification(operation, OperationStatuses.Succeeded, now));
             await db.SaveChangesAsync(cancellationToken);
             if (transaction is not null) await transaction.CommitAsync(cancellationToken);