fix: improve cross-device evidence, request diagnostics and prompt efficiency

artemis/data_engine/engine.py

@@ -1314,10 +1314,12 @@ class DataEngine:
 
     def get_step_image_path(self, step_number: int, which: str = "pre") -> Path | None:
         """Read-only path of a step's pre/post screenshot, if recorded."""
+        from artemis.data_engine.step_evidence import step_image_name
+
         step = self.get_step_record(step_number)
         if step is None:
             return None
-        image_name = step.pre_image_name if which == "pre" else step.post_image_name
+        image_name = step_image_name(step, which)
         if not image_name:
             return None
         path = self.get_image_path(image_name)