test: add one projected x-gap-width shear contrast

tests/validation/taylor_green/shear_wide_x.py

@@ -0,0 +1,20 @@
+"""One projected x-gap-width diagnostic (opt-in wide_x_shear_n128).
+
+Keep the nested outer boxes and all three spacings. Shrink only L2 in x,
+so each x-normal middle gap grows from 6 to 12 root cells; y gaps stay 6.
+This also reduces L2 volume and moves its x faces. It is a descriptive
+geometry contrast with no new qualification matrix, assessor or pass gate.
+"""
+
+import shear_nested as nested
+
+ROOT_N = nested.ROOT_N
+DEPTH = nested.DEPTH
+REFINEMENTS = [nested.REFINEMENTS[0],
+               [(56, 44, 96, 212), (160, 60, 200, 228)]]  # parent L1 coordinates
+CASES = ((100, ROOT_N, DEPTH, "projected_linear"),)
+LEAVES = [7936, 20352, 53760]
+HOPS = nested.HOPS
+WORK = sum(c * h for c, h in zip(LEAVES, HOPS))  # 540016640 active updates
+NU = nested.NU
+TAU = nested.TAU