Constant MAX_FIELD_PATH_DEPTH 

pub const MAX_FIELD_PATH_DEPTH: usize = 8;

How deep a field path first_unbounded will name before it stops.

ROS message nesting is shallow in practice (PoseStamped.header.stamp.sec is three), and this walk runs on no_std with no allocator, so the path is a fixed array rather than a Vec. A deeper type still reports — the path is simply truncated, and UnboundedField::truncated says so, because a path that silently stops short would point at the wrong member.