refactor(dotnet): normalize learning dataset export inputs

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

@@ -0,0 +1,54 @@
+using Moq;
+using QuantEngine.Application.Services;
+using QuantEngine.Core.Interfaces;
+
+namespace QuantEngine.Core.Tests;
+
+public class LearningDatasetServiceTests
+{
+    [Fact]
+    public async Task ExportJsonAsync_TrimsPathAndClampsLimit()
+    {
+        var reader = new Mock<ILearningDatasetReader>(MockBehavior.Strict);
+        reader.Setup(r => r.ReadTrainingExamplesAsync(10000)).ReturnsAsync([]);
+
+        var service = new LearningDatasetService(reader.Object);
+        var root = FindRepoRoot();
+        var outPath = Path.Combine(root, "Temp", "learning_dataset_test.json");
+
+        if (File.Exists(outPath))
+        {
+            File.Delete(outPath);
+        }
+
+        var result = await service.ExportJsonAsync($"  {outPath}  ", 50000);
+
+        Assert.Equal(Path.GetFullPath(outPath), result);
+        Assert.True(File.Exists(result));
+        var text = await File.ReadAllTextAsync(result);
+        Assert.Contains("\"gate\": \"DATA_MISSING\"", text);
+        reader.VerifyAll();
+    }
+
+    [Fact]
+    public async Task ExportJsonAsync_RejectsBlankPath()
+    {
+        var service = new LearningDatasetService(new Mock<ILearningDatasetReader>().Object);
+        await Assert.ThrowsAsync<ArgumentException>(() => service.ExportJsonAsync(" ", 10));
+    }
+
+    private static string FindRepoRoot()
+    {
+        var current = new DirectoryInfo(AppContext.BaseDirectory);
+        while (current != null)
+        {
+            if (Directory.Exists(Path.Combine(current.FullName, ".git")))
+            {
+                return current.FullName;
+            }
+            current = current.Parent;
+        }
+
+        throw new InvalidOperationException("Repository root not found.");
+    }
+}