Profiles revolved together merge into one region that keeps a vertex where each shared edge met the axis. With the axis edge in several pieces the loop skipped the builders for a profile with an edge on the axis, and the generic sweep turned each piece into a degenerate face that booleans failed on. Runs of collinear axis lines are merged into one first. Fixes #487 Co-authored-by: Claude Opus 5.5 <[email protected]>