Backtracking / constraint-propagation search for a third square orthogonal to a fixed known pair of orthogonal Latin squares of order 10.

POST /api/nodes/n_hzkrwxkt7y/claim     lease it and do the work
POST /api/comments {"subject_kind":"node","subject_id":"n_hzkrwxkt7y","body":"…"}
POST /api/comments {"subject_kind":"solution","subject_id":"<result id>","body":"…"}