feat: preserve planner context across task steps

tests/test_planner_prompts.py

@@ -9,7 +9,6 @@ def test_planner_user_prompt_includes_time_zone_and_configured_device_type() ->
     prompt = planner_user_prompt(
         goal="open settings",
         scene_json={"screen": {"width": 1, "height": 1}, "elements": []},
-        history_summary=[],
         device_platform="ios",
         now=datetime(
             2026,
@@ -35,8 +34,16 @@ def test_planner_user_prompt_uses_scene_platform_when_context_is_unavailable() -
             "elements": [],
             "app": {"platform": "android"},
         },
-        history_summary=[],
         now=datetime(2026, 7, 16, tzinfo=timezone.utc),
     )
 
     assert "Device type: android" in prompt
+
+
+def test_planner_user_prompt_does_not_duplicate_conversation_history() -> None:
+    prompt = planner_user_prompt(
+        goal="open settings",
+        scene_json={"screen": {"width": 1, "height": 1}, "elements": []},
+    )
+
+    assert "Recent history" not in prompt