refactor(dotnet): validate raw history ingestion payloads

src/dotnet/QuantEngine.Application/Services/HistoryIngestionService.cs

@@ -15,16 +15,16 @@ namespace QuantEngine.Application.Services
         }
 
         public Task<int> AppendDecisionAsync(IDictionary<string, object?> payload)
-            => _store.AppendAsync("decision_result_history", payload);
+            => _store.AppendAsync("decision_result_history", RequirePayload(payload));
 
         public Task<int> AppendFactorOutputAsync(IDictionary<string, object?> payload)
-            => _store.AppendAsync("factor_output_history", payload);
+            => _store.AppendAsync("factor_output_history", RequirePayload(payload));
 
         public Task<int> AppendMarketRawAsync(IDictionary<string, object?> payload)
-            => _store.AppendAsync("market_raw_history", payload);
+            => _store.AppendAsync("market_raw_history", RequirePayload(payload));
 
         public Task<int> AppendGapAsync(IDictionary<string, object?> payload)
-            => _store.AppendAsync("market_vs_engine_gap_history", payload);
+            => _store.AppendAsync("market_vs_engine_gap_history", RequirePayload(payload));
 
         public Task<int> AppendDecisionAsync(
             FinalDecisionResult decision,
@@ -113,5 +113,11 @@ namespace QuantEngine.Application.Services
 
         private static string? NormalizeOptional(string? value)
             => string.IsNullOrWhiteSpace(value) ? null : value.Trim();
+
+        private static IDictionary<string, object?> RequirePayload(IDictionary<string, object?> payload)
+        {
+            ArgumentNullException.ThrowIfNull(payload);
+            return payload;
+        }
     }
 }

src/dotnet/QuantEngine.Core.Tests/HistoryIngestionServiceTests.cs

@@ -48,4 +48,12 @@ public class HistoryIngestionServiceTests
             1.0,
             "PASS"));
     }
+
+    [Fact]
+    public async Task AppendDecisionAsync_RejectsNullRawPayload()
+    {
+        var service = new HistoryIngestionService(new Mock<IPostgresqlHistoryStore>().Object);
+
+        await Assert.ThrowsAsync<ArgumentNullException>(() => service.AppendDecisionAsync((IDictionary<string, object?>)null!));
+    }
 }