Module shell 

Shell validation checks.

Functions

check_shell_closed

Check shell closure: every edge shared by exactly 2 faces.

check_shell_connected

Check shell connectivity: all faces connected via shared edges (BFS).

check_shell_empty

Check shell is not empty.

check_shell_orientation

Check that shell face orientations are consistent: for each edge shared by two faces, it should be used once FORWARD and once REVERSED.