Function b2RecPlayer_GetBodyId 

pub unsafe extern "C" fn b2RecPlayer_GetBodyId(
    player: *const b2RecPlayer,
    index: c_int,
) -> b2BodyId

Get a tracked body by creation ordinal. Returns b2_nullBodyId for a destroyed slot, an ordinal not yet reached at the current frame, or an out-of-range index. Validate with b2Body_IsValid.