Function resolve_call_output_path 

pub fn resolve_call_output_path(
    history: &[Message],
    call_id: &str,
) -> Option<PathBuf>

The file a call’s output went to, from the frames a conversation carries.

Two ways to find it, and the ending frame’s own word wins when both exist: task_notification.output_file names the file when the task ends, and until then the path is composed from the task id the launch frame carries, under task_output_base. An empty output_file is a path the frame does not carry, not a path that is gone.