fix: bound task failures and release stalled workers

tests/unit/agents/test_planner_node.py

@@ -33,6 +33,17 @@ class DummyState:
         self.operator_replan_reason = operator_replan_reason
 
 
+import base64
+from io import BytesIO
+from PIL import Image
+
+
+def _valid_screen_base64():
+    buffer = BytesIO()
+    Image.new("RGB", (64, 64), "white").save(buffer, format="PNG")
+    return base64.b64encode(buffer.getvalue()).decode("ascii")
+
+
 @pytest.fixture
 def mock_context():
     ctx = Mock(spec=ArtemisContext)
@@ -41,7 +52,7 @@ def mock_context():
     ctx.adb_client = Mock()
     ctx.ui_adb_client = Mock()
     mock_screen_data = Mock()
-    mock_screen_data.base64 = "YmFzZTY0"
+    mock_screen_data.base64 = _valid_screen_base64()
     mock_screen_data.elements = []
     mock_screen_data.width = 1080
     mock_screen_data.height = 2400