Function paste_pattern 

pub fn paste_pattern(
    assets: &mut Assets,
    clip: &SfxClip,
    at_pattern: usize,
) -> PasteReport

Music-editor paste: append the clip’s SFX after the last used SFX slot (non-destructive), remap each footer pattern’s channel refs to where those SFX landed, then overwrite music patterns from at_pattern.