feat: add Android task file evidence and finalize plugin design

tests/unit/data_engine/test_latency_optimizations_deep.py

@@ -197,6 +197,15 @@ async def test_perception_node_async_offloading(mock_artemis_ctx, tmp_path):
     engine = DataEngine(mock_artemis_ctx)
     engine.start_session("Test Perception Node Offloading")
     mock_artemis_ctx.data_engine = engine
+    image_saved = asyncio.Event()
+    loop = asyncio.get_running_loop()
+    save_image = engine.get_or_create_image
+
+    def save_image_and_signal(*args, **kwargs):
+        try:
+            return save_image(*args, **kwargs)
+        finally:
+            loop.call_soon_threadsafe(image_saved.set)
 
     # Create an injected_instruction.json file
     instruction_file = Path(engine.base_dir) / "injected_instruction.json"
@@ -214,6 +223,7 @@ async def test_perception_node_async_offloading(mock_artemis_ctx, tmp_path):
     mock_screen_data.height = 2400
 
     with (
+        patch.object(engine, "get_or_create_image", side_effect=save_image_and_signal),
         patch("artemis.graph.perception.UnifiedMobileController") as mock_controller_cls,
         patch("artemis.graph.perception.perform_ocr", new_callable=AsyncMock) as mock_ocr,
         patch("artemis.graph.perception._detect_status_bar_height", return_value=0),
@@ -240,10 +250,9 @@ async def test_perception_node_async_offloading(mock_artemis_ctx, tmp_path):
     # Verify injected_instruction.json was unlinked
     assert not instruction_file.exists()
 
-    # Await background tasks triggered by perception_node
-    await asyncio.sleep(0.1)
-    if engine._pending_tasks:
-        await asyncio.gather(*engine._pending_tasks)
+    # perception_node creates its own task, outside engine._pending_tasks.
+    # Wait for actual persistence instead of assuming the disk finishes in 100 ms.
+    await asyncio.wait_for(image_saved.wait(), timeout=5)
 
     # Verify image record and file were created in background by perception_node
     img_record = engine.storage.get_image(expected_hash)