fix: retry with backoff for 429 rate-limit on question fetch

app.py

@@ -629,14 +629,28 @@ def run_and_submit_all(profile: gr.OAuthProfile | None):
     space_id = os.getenv("SPACE_ID", "ngbaoan/Final_Assignment_AI_agents_course")
     agent_code = f"https://huggingface.co/spaces/{space_id}/tree/main"
 
-    # 1 — Fetch questions
+    # 1 — Fetch questions (retry up to 5× with backoff for 429)
     yield "📡 Fetching GAIA questions…", None
-    try:
-        resp = requests.get(QUESTIONS_URL, timeout=20)
-        resp.raise_for_status()
-        questions_data = resp.json()
-    except Exception as exc:
-        yield f"❌ Failed to fetch questions: {exc}", None
+    questions_data = None
+    for attempt in range(1, 6):
+        try:
+            resp = requests.get(QUESTIONS_URL, timeout=30)
+            if resp.status_code == 429:
+                wait_sec = 10 * attempt          # 10s, 20s, 30s, 40s, 50s
+                yield f"⏳ Rate-limited (429). Waiting {wait_sec}s before retry {attempt}/5…", None
+                import time; time.sleep(wait_sec)
+                continue
+            resp.raise_for_status()
+            questions_data = resp.json()
+            break
+        except Exception as exc:
+            if attempt == 5:
+                yield f"❌ Failed to fetch questions after 5 attempts: {exc}", None
+                return
+            import time; time.sleep(10 * attempt)
+
+    if not questions_data:
+        yield "❌ No questions received.", None
         return
 
     total = len(questions_data)