feat: settle mobile observations before summarizing steps

tests/unit/agents/test_flash_step_summarizer.py

@@ -468,6 +468,8 @@ async def test_dual_frame_dispatch_keeps_transition_prompt(mock_context):
         pre_img_bytes=b"pre",
         post_img_bytes=b"post",
         exec_outcome="executed",
+        post_ui_elements_text="[1] Text: '存储空间' | Bounds: [0,0][100,100]",
+        observation_settled=False,
     )
     await summarizer.flush()
 
@@ -477,6 +479,10 @@ async def test_dual_frame_dispatch_keeps_transition_prompt(mock_context):
     assert "Before/After screenshots" in system_text
     assert "--- [1] BEFORE ACTION SCREEN (Action Marked Visually in Red) ---" in human_text
     assert "--- [2] AFTER ACTION SCREEN ---" in human_text
+    assert "--- [3] AFTER ACTION UI ELEMENTS ---" in human_text
+    assert "Text: '存储空间'" in human_text
+    assert "screen still changing" in human_text
+    assert "hierarchy names the new page" in system_text
     assert "DECISION FRAME" not in human_text