fix(artifacts): prioritize PDF deliverables in sidebar

lib/runtime/desktop_thread_artifact_service.dart

@@ -270,6 +270,20 @@ class DesktopThreadArtifactService {
       }
     }
     entries.sort((a, b) {
+      final deliveryCompare = artifactDisplayPriorityInternal(
+        a.relativePath,
+      ).compareTo(artifactDisplayPriorityInternal(b.relativePath));
+      if (deliveryCompare != 0) {
+        return deliveryCompare;
+      }
+      if (fileExtensionInternal(a.relativePath) == 'pdf') {
+        final depthCompare = artifactPathDepthInternal(
+          a.relativePath,
+        ).compareTo(artifactPathDepthInternal(b.relativePath));
+        if (depthCompare != 0) {
+          return depthCompare;
+        }
+      }
       final updatedCompare = (b.updatedAtMs ?? 0).compareTo(a.updatedAtMs ?? 0);
       if (updatedCompare != 0) {
         return updatedCompare;
@@ -279,6 +293,16 @@ class DesktopThreadArtifactService {
     return entries;
   }
 
+  static int artifactDisplayPriorityInternal(String relativePath) {
+    return fileExtensionInternal(relativePath) == 'pdf' ? 0 : 1;
+  }
+
+  static int artifactPathDepthInternal(String relativePath) {
+    return normalizeArtifactPathInternal(
+      relativePath,
+    ).split('/').where((segment) => segment.isNotEmpty).length;
+  }
+
   Future<List<AssistantArtifactEntry>> buildResultEntriesInternal({
     required List<AssistantArtifactChangeEntry> changes,
     required List<AssistantArtifactEntry> fileEntries,

test/runtime/desktop_thread_artifact_service_test.dart

@@ -65,6 +65,49 @@ void main() {
     },
   );
 
+  test(
+    'loadSnapshot shows the root PDF deliverable before supporting files',
+    () async {
+      final workspace = await Directory.systemTemp.createTemp(
+        'xworkmate-pdf-artifact-order-',
+      );
+      addTearDown(() async {
+        if (await workspace.exists()) {
+          await workspace.delete(recursive: true);
+        }
+      });
+      await Directory(
+        '${workspace.path}/assets/diagrams',
+      ).create(recursive: true);
+      await File(
+        '${workspace.path}/assets/diagrams/chapter.png',
+      ).writeAsBytes(<int>[1, 2, 3]);
+      await File(
+        '${workspace.path}/assets/安全架构演进白皮书.pdf',
+      ).writeAsBytes(<int>[4, 5, 6]);
+      await File(
+        '${workspace.path}/安全架构演进白皮书.pdf',
+      ).writeAsBytes(<int>[4, 5, 6]);
+
+      final snapshot = await DesktopThreadArtifactService().loadSnapshot(
+        workspacePath: workspace.path,
+        workspaceKind: WorkspaceRefKind.localPath,
+        artifactRelativePaths: const <String>[
+          'assets/diagrams/chapter.png',
+          'assets/安全架构演进白皮书.pdf',
+          '安全架构演进白皮书.pdf',
+        ],
+      );
+
+      expect(snapshot.fileEntries.map((entry) => entry.relativePath), <String>[
+        '安全架构演进白皮书.pdf',
+        'assets/安全架构演进白皮书.pdf',
+        'assets/diagrams/chapter.png',
+      ]);
+      expect(snapshot.resultEntries.first.mimeType, 'application/pdf');
+    },
+  );
+
   test(
     'loadPreview rejects historical files outside current task artifacts',
     () async {