Closed-chain consistency under SR + PDS
Each chain: source-degenerate T_1 ... outer-triangle T_n.

chain                                                   trajectory                               outer-perm
--------------------------------------------------------------------------------------------------------------
  (5,1) | (6,5) | (5,6) | (3,5)                         30→132→60→6                                       ✓
  (5,1) | (7,5) | (5,7) | (3,5)                         30→312→60→6                                       ✓
  (5,1) | (8,5) | (6,8) | (3,6)                         30→708→183→6                                      ✓
  (5,1) | (8,5) | (8,8) | (5,8) | (3,5)                 30→708→1476→60→6                                  ✓
  (6,1) | (7,6) | (5,7) | (3,5)                         63→348→60→6                                       ✓
  (6,1) | (8,6) | (6,8) | (3,6)                         63→783→183→6                                      ✓
  (6,1) | (9,6) | (8,9) | (5,8) | (3,5)                 63→1836→1623→60→6                                 ✓
  (5,1) | (6,5) | (8,6) | (9,8) | (8,9) | (6,8) | (3,6) 30→132→1260→4800→1641→183→6                       ✓
  (6,1) | (8,6) | (10,8) | (10,10) | (8,10) | (5,8) | (3,5) 63→783→9993→14643→1641→60→6                       ✓
  (7,1) | (9,7) | (7,9) | (3,7)                         126→2130→546→6                                    ✓
