=== 15a: slant -> 0 must reproduce the VERTICAL solver ===
  te slant=1e-09: max|dR|=2.135e-10 max|dT|=1.104e-10 tot-1=-3.24e-10
  te slant=1e-06: max|dR|=6.613e-10 max|dT|=7.047e-09 tot-1=-6.39e-09
  te slant=1e-03: max|dR|=5.973e-07 max|dT|=5.997e-07 tot-1=-2.37e-09
  tm slant=1e-09: max|dR|=2.425e-09 max|dT|=2.983e-09 tot-1=+5.41e-09
  tm slant=1e-06: max|dR|=9.888e-11 max|dT|=4.523e-09 tot-1=-4.42e-09
  tm slant=1e-03: max|dR|=1.846e-06 max|dT|=1.836e-06 tot-1=+1.05e-08

=== 15b: 20 deg slant vs an RCWA z-staircase ===
  te PMM(single slanted layer, deg 24): R0=0.238809459 R-1=0.000000000 T0=0.761190541 tot=1.0000000001
Traceback (most recent call last):
  File "docs/audits/AUDIT_ADVERSARIAL_EXHAUSTIVE_2026_09_11/repro/PMM-1D\p15_slant.py", line 65, in <module>
    st.add_layer(dz, segments=segs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^
TypeError: RCWAStack.add_layer() got an unexpected keyword argument 'segments'
