research: Dütsch driver — periodic Morison bases from step mod T

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

research/duetsch_re100_kc5/protocol.py

@@ -53,7 +53,7 @@ def interval_bases(n, T, points=16):
     """Single-step interval averages over [n, n + 1] of cos phi |cos phi| and sin phi
     (phi in radians = 2 pi s / T - pi / 2), Gauss-Legendre quadrature."""
     x, w = np.polynomial.legendre.leggauss(points)
-    s = n + 0.5 * (x + 1.0)
+    s = int(n) % T + 0.5 * (x + 1.0)  # periodic: identical bases in every cycle
     phi = 2.0 * np.pi * s / T - 0.5 * np.pi
     c = np.cos(phi)
     return 0.5 * float(np.sum(w * c * np.abs(c))), 0.5 * float(np.sum(w * np.sin(phi)))