Function partial_progress_frames 

pub fn partial_progress_frames(
    input: &str,
    max_delta_bytes: usize,
    max_frame_bytes: usize,
) -> Vec<ToolProgress>

Split input into UTF-8-safe partial progress frames.

Each frame’s delta is at most max_delta_bytes and ends on a char boundary. Stops once cumulative bytes would exceed max_frame_bytes.