feat(planner): add execution context to prompts

tests/test_ai_planner.py

@@ -146,6 +146,22 @@ def test_ai_planner_forwards_tools_screenshot_and_timeout_to_client() -> None:
     assert "send a message" in call["user_prompt"]
 
 
+def test_ai_planner_includes_device_platform_from_task_context() -> None:
+    client = FakeToolCallingClient(
+        ToolCallDecision(tool_name="tap", arguments={"x": 1, "y": 2})
+    )
+    planner = AIPlanner(client=client)
+    context = TaskContext(
+        task_id="task-1",
+        goal="send a message",
+        device_platform="android",
+    )
+
+    planner.plan(goal="send a message", scene=_scene(), context=context)
+
+    assert "Device type: android" in client.calls[0]["user_prompt"]
+
+
 def test_ai_planner_populates_step_prompt_from_user_prompt() -> None:
     """PlannedStep.prompt should carry the actual user prompt sent to the LLM,
     not the bare task goal."""