fix(chat): handle empty uploaded files case and improve artifact selection logic (#979)

* fix(chat): handle empty uploaded files case and improve artifact selection logic

* Update frontend/src/components/workspace/chats/chat-box.tsx

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* fix: address code review suggestions from PR #979 (#3)

* Initial plan

* fix: address PR #979 review suggestions

- utils.ts: scope (empty) check inside <uploaded_files> tag content
- chat-box.tsx: remove stale `artifacts` from useEffect deps
- context.tsx: wrap select/deselect with useCallback for stable refs
- test: add test_empty_new_files_produces_empty_marker

Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot <198982749+Copilot@users.noreply.github.com>
Co-authored-by: foreleven <4785594+foreleven@users.noreply.github.com>

frontend/src/core/messages/utils.ts

@@ -300,6 +300,11 @@ export function parseUploadedFiles(content: string): FileInMessage[] {
     return [];
   }
 
+  // Check if the backend reported no new files were uploaded in this message
+  if (uploadedFilesContent?.includes("(empty)")) {
+    return [];
+  }
+
   // Parse file list
   // Format: - filename (size)\n  Path: /path/to/file
   const fileRegex = /- ([^\n(]+)\s*\(([^)]+)\)\s*\n\s*Path:\s*([^\n]+)/g;