fix: do up No audit of document access in vigilcare-records-gap-analysis.md

VigilCareRecordsAPI/Services/BatchService.cs

@@ -73,6 +73,18 @@ public class BatchService : IBatchService
         // Duplicate detection: same SHA-256 for same patient within 24 hours
         if (patientId.HasValue)
         {
+            // Atomic Redis guard prevents concurrent uploads from racing past the DB check
+            var cache = _redis.GetDatabase();
+            var dedupKey = $"batch:dedup:{sha256}:{patientId.Value}";
+            var acquired = await cache.StringSetAsync(dedupKey, "1",
+                TimeSpan.FromHours(24), When.NotExists);
+
+            if (!acquired)
+                throw new ConflictException(
+                    "A document with the same content was uploaded for this patient within the last 24 hours.",
+                    "DUPLICATE_DOCUMENT");
+
+            // DB fallback for dedup entries created before Redis guard was deployed
             var cutoff = DateTimeOffset.UtcNow.AddHours(-24);
             var duplicate = await _db.DigitizationBatches.AnyAsync(b =>
                 b.DocumentSha256 == sha256 &&
@@ -80,9 +92,12 @@ public class BatchService : IBatchService
                 b.CreatedAt >= cutoff);
 
             if (duplicate)
+            {
+                await cache.KeyDeleteAsync(dedupKey);
                 throw new ConflictException(
                     "A document with the same content was uploaded for this patient within the last 24 hours.",
                     "DUPLICATE_DOCUMENT");
+            }
         }
 
         var batchId = Guid.NewGuid();