Add explicit source-metadata fallback coverage

Author: Copilot

src/Microsoft.DotNet.Helix/Sdk.Tests/Microsoft.DotNet.Helix.Sdk.Tests/HelixServiceTests.cs

@@ -306,6 +306,51 @@ await CreateService(api.Api.Object, blobClientFactory)
             Assert.Null(capturedRequest.Branch);
         }
 
+        [Fact]
+        public async Task ResubmitWorkItemsAsync_FallsBackToParsingSourceWhenPropertiesAreMissing()
+        {
+            var api = CreateApi();
+            api.Job
+                .Setup(j => j.DetailsAsync("original-job", It.IsAny<CancellationToken>()))
+                .ReturnsAsync(JobDetails(source: "ci/public/dotnet/arcade/refs/heads/main", includeSourceMetadataInProperties: false));
+            api.Storage
+                .Setup(s => s.NewAsync(It.IsAny<ContainerCreationRequest>(), It.IsAny<CancellationToken>()))
+                .ReturnsAsync(new ContainerInformation(
+                    DateTimeOffset.Parse("2026-04-30T00:00:00Z"),
+                    DateTimeOffset.Parse("2026-05-30T00:00:00Z"),
+                    "creator",
+                    "container",
+                    "account",
+                    Guid.Empty,
+                    "region")
+                {
+                    ReadToken = "?read",
+                    WriteToken = "?write",
+                });
+
+            JobCreationRequest capturedRequest = null;
+            api.Job
+                .Setup(j => j.NewAsync(It.IsAny<JobCreationRequest>(), It.IsAny<string>(), null, It.IsAny<CancellationToken>()))
+                .Callback<JobCreationRequest, string, bool?, CancellationToken>((request, _, _, _) => capturedRequest = request)
+                .ReturnsAsync(new JobCreationResult("new-job", "summary", "results", null));
+
+            var blobClientFactory = new FakeBlobClientFactory
+            {
+                DownloadedText = """[{ "WorkItemId": "work-a", "Command": "run a", "PayloadUri": "payload-a" }]""",
+                UploadedBlobUri = new Uri("https://account.blob.core.windows.net/container/job-list.json"),
+            };
+
+            await CreateService(api.Api.Object, blobClientFactory)
+                .ResubmitWorkItemsAsync(new HelixJobInfo("original-job", "finished"), [WorkItem("work-a")], CancellationToken.None);
+
+            Assert.NotNull(capturedRequest);
+            Assert.Null(capturedRequest.Source);
+            Assert.Equal("ci", capturedRequest.SourcePrefix);
+            Assert.Equal("public", capturedRequest.TeamProject);
+            Assert.Equal("dotnet/arcade", capturedRequest.Repository);
+            Assert.Equal("refs/heads/main", capturedRequest.Branch);
+        }
+
         private static HelixService CreateService(IHelixApi api, IBlobClientFactory blobClientFactory = null, IFileSystem fileSystem = null)
             => new(
                 api,