fix: use /.github/workflows/ marker for derivation parsing

Fixes incorrect parsing for repos named .github (e.g. octo-org/.github).
The old /.github/ marker would match too early, deriving the wrong
repository name. Also treats empty-string fields as unset during derivation.

src/Runner.Worker/JobContext.cs

@@ -159,25 +159,27 @@ namespace GitHub.Runner.Worker
                 return;
             }
 
-            // Format: owner/repo/path/to/file.yml@ref
+            // Format: owner/repo/.github/workflows/file.yml@ref
             var atIndex = workflowRef.IndexOf('@');
             var pathPart = atIndex >= 0 ? workflowRef.Substring(0, atIndex) : workflowRef;
 
-            // Split into owner/repo and file path at the .github/ boundary
+            // Split at /.github/workflows/ to correctly handle repos named ".github"
-            var githubDirIndex = pathPart.IndexOf("/.github/");
+            // e.g. "octo-org/.github/.github/workflows/ci.yml" → repo="octo-org/.github"
-            if (githubDirIndex < 0)
+            var marker = "/.github/workflows/";
+            var markerIndex = pathPart.IndexOf(marker);
+            if (markerIndex < 0)
             {
                 return;
             }
 
-            if (WorkflowRepository == null)
+            if (WorkflowRepository == null || WorkflowRepository == "")
             {
-                WorkflowRepository = pathPart.Substring(0, githubDirIndex);
+                WorkflowRepository = pathPart.Substring(0, markerIndex);
             }
 
-            if (WorkflowFilePath == null)
+            if (WorkflowFilePath == null || WorkflowFilePath == "")
             {
-                WorkflowFilePath = pathPart.Substring(githubDirIndex + 1); // skip leading '/'
+                WorkflowFilePath = pathPart.Substring(markerIndex + 1); // skip leading '/'
             }
         }
     }

src/Test/L0/Worker/JobContextL0.cs

@@ -194,5 +194,30 @@ namespace GitHub.Runner.Common.Tests.Worker
             Assert.Equal("my-org/my-repo", ctx.WorkflowRepository);
             Assert.Equal(".github/workflows/deploy.yml", ctx.WorkflowFilePath);
         }
+
+        [Fact]
+        public void DeriveWorkflowRefComponents_HandlesDotGithubRepoName()
+        {
+            // Repos can be named ".github" — the marker must be /.github/workflows/ not /.github/
+            var ctx = new JobContext();
+            ctx.WorkflowRef = "octo-org/.github/.github/workflows/ci.yml@refs/heads/main";
+            ctx.DeriveWorkflowRefComponents();
+
+            Assert.Equal("octo-org/.github", ctx.WorkflowRepository);
+            Assert.Equal(".github/workflows/ci.yml", ctx.WorkflowFilePath);
+        }
+
+        [Fact]
+        public void DeriveWorkflowRefComponents_TreatsEmptyStringAsUnset()
+        {
+            var ctx = new JobContext();
+            ctx.WorkflowRef = "my-org/my-repo/.github/workflows/deploy.yml@refs/heads/main";
+            ctx.WorkflowRepository = "";
+            ctx.WorkflowFilePath = "";
+            ctx.DeriveWorkflowRefComponents();
+
+            Assert.Equal("my-org/my-repo", ctx.WorkflowRepository);
+            Assert.Equal(".github/workflows/deploy.yml", ctx.WorkflowFilePath);
+        }
     }
 }