fix(sleepers): no rail left lying on a timber without a fastening: the stock rails on a plate as wide as their foot between the brace and the slide plate, the stock rails back to back, as the wing rails of the slips with the blades outside of the diamond, on one plate under both; three rails or more close beside one another under fastenings of two rails in turn; a plate lying over the fastening of the rail beside cut short at its edge, as on one plate with it, a rail with its check rail on the fastening of the rail beside in such a plate, not left out; selftests checkseats and the bare rails in fastencheck

world/SleeperRules.h

@@ -62,6 +62,8 @@ double constexpr check_seats { 0.113 };
 // the room left between the fastenings of rails close by, and how narrow their plates get to keep it
 double constexpr fastening_gap { 0.01 };
 double constexpr plate_least { 0.6 };
+// a plate cut short at the fastening of the rail beside, as on one plate with it, no narrower than this
+double constexpr clip_least { 0.4 };
 double constexpr slide_least { 0.25 };
 // a fastening of two rails narrowed no more than this, the rails lying a little off its seats then
 double constexpr check_least { 0.8 };