A constant-radius fillet whose setback equals the width of a neighbouring
face was refused ("the blend is larger than the neighbouring faces"), so
r = 3 on the vertical edges of a 6 mm wide box failed while 2.999 worked.
The corner edge is now consumed: the rail ends at its far vertex and a side
face used up at both ends is removed, its remaining edge becoming the rail.
A face used up at one end only, and radii past the limit, are still refused.
Refs #199
Claude-Session: https://claude.ai/code/session_01TWc1smHYwTSVrVc8SNvS44
Co-authored-by: Claude Opus 5.5 <[email protected]>
