diff --git a/src/dotnet/QuantEngine.Application/Services/CollectionReadModelService.cs b/src/dotnet/QuantEngine.Application/Services/CollectionReadModelService.cs
index beb28ab4..6b2dc85c 100644
--- a/src/dotnet/QuantEngine.Application/Services/CollectionReadModelService.cs
+++ b/src/dotnet/QuantEngine.Application/Services/CollectionReadModelService.cs
@@ -13,9 +13,31 @@ public sealed class CollectionReadModelService : ICollectionReadModelService
     }
 
     public Task<CollectionDashboardStateRecord> GetDashboardStateAsync() => _repository.GetDashboardStateAsync();
-    public Task<List<CollectionRunRecord>> GetRecentRunsAsync(int limit = 20) => _repository.GetRecentRunsAsync(limit);
-    public Task<List<CollectionSnapshotRecord>> GetRunSnapshotsAsync(string runId) => _repository.GetRunSnapshotsAsync(runId);
-    public Task<List<CollectionErrorRecord>> GetRunErrorsAsync(string runId, int limit = 50) => _repository.GetRunErrorsAsync(runId, limit);
-    public Task<List<CollectionSnapshotRecord>> GetLatestSnapshotsForTickerAsync(string ticker, int limit = 10) => _repository.GetLatestSnapshotsForTickerAsync(ticker, limit);
+
+    public Task<List<CollectionRunRecord>> GetRecentRunsAsync(int limit = 20)
+        => _repository.GetRecentRunsAsync(NormalizeLimit(limit, 1, 200));
+
+    public Task<List<CollectionSnapshotRecord>> GetRunSnapshotsAsync(string runId)
+        => _repository.GetRunSnapshotsAsync(RequireValue(runId, nameof(runId)));
+
+    public Task<List<CollectionErrorRecord>> GetRunErrorsAsync(string runId, int limit = 50)
+        => _repository.GetRunErrorsAsync(RequireValue(runId, nameof(runId)), NormalizeLimit(limit, 1, 200));
+
+    public Task<List<CollectionSnapshotRecord>> GetLatestSnapshotsForTickerAsync(string ticker, int limit = 10)
+        => _repository.GetLatestSnapshotsForTickerAsync(RequireValue(ticker, nameof(ticker)), NormalizeLimit(limit, 1, 100));
+
     public Task<List<PriceHistorySummaryRecord>> GetPriceHistorySummaryAsync() => _repository.GetPriceHistorySummaryAsync();
+
+    private static string RequireValue(string value, string parameterName)
+    {
+        if (string.IsNullOrWhiteSpace(value))
+        {
+            throw new ArgumentException("Value is required.", parameterName);
+        }
+
+        return value.Trim();
+    }
+
+    private static int NormalizeLimit(int limit, int min, int max)
+        => Math.Clamp(limit, min, max);
 }
diff --git a/src/dotnet/QuantEngine.Core.Tests/CollectionReadModelServiceTests.cs b/src/dotnet/QuantEngine.Core.Tests/CollectionReadModelServiceTests.cs
new file mode 100644
index 00000000..143f22c8
--- /dev/null
+++ b/src/dotnet/QuantEngine.Core.Tests/CollectionReadModelServiceTests.cs
@@ -0,0 +1,44 @@
+using Moq;
+using QuantEngine.Application.Services;
+using QuantEngine.Core.Interfaces;
+
+namespace QuantEngine.Core.Tests;
+
+public class CollectionReadModelServiceTests
+{
+    [Fact]
+    public async Task GetRecentRunsAsync_ClampsLimitToUpperBound()
+    {
+        var repo = new Mock<ICollectionReadRepository>(MockBehavior.Strict);
+        repo.Setup(r => r.GetRecentRunsAsync(200)).ReturnsAsync([]);
+
+        var service = new CollectionReadModelService(repo.Object);
+
+        var result = await service.GetRecentRunsAsync(999);
+
+        Assert.Empty(result);
+        repo.VerifyAll();
+    }
+
+    [Fact]
+    public async Task GetLatestSnapshotsForTickerAsync_TrimsTickerAndClampsLimit()
+    {
+        var repo = new Mock<ICollectionReadRepository>(MockBehavior.Strict);
+        repo.Setup(r => r.GetLatestSnapshotsForTickerAsync("005930", 100)).ReturnsAsync([]);
+
+        var service = new CollectionReadModelService(repo.Object);
+
+        var result = await service.GetLatestSnapshotsForTickerAsync(" 005930 ", 999);
+
+        Assert.Empty(result);
+        repo.VerifyAll();
+    }
+
+    [Fact]
+    public async Task GetRunErrorsAsync_RejectsEmptyRunId()
+    {
+        var service = new CollectionReadModelService(new Mock<ICollectionReadRepository>().Object);
+
+        await Assert.ThrowsAsync<ArgumentException>(() => service.GetRunErrorsAsync("  ", 10));
+    }
+}