pre-step gate MEASURED: repairs 77.5% -> 15.9%, CHA hits the ITP target for the first time (2851 <= 2857), two sets 7440 (best of the line) — but APS grows 2806 -> 4449, so by the pre-registered stop rule the mode is NOT accepted. Cause named: my gate refuses on BRACKET PROGRESS, and this project had already measured that currency to be wrong (a secant step collapses the error while barely moving the bracket: 150 vs 86). Chandrupatla refuses on the SHAPE of the configuration. Next candidate derived, not borrowed: slope-stability gate

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

explain_chandrupatla.py

@@ -97,8 +97,9 @@ def chandrupatla_traced(f, a, b, xtol, maxfev):
         return float("nan"), g.n, False, trace
 
 
-def main():
+def main(prestep="none"):
     probs = [p for p in load_problems() if p[0] == "CHA"]
+    print(f"ours: prestep={prestep!r}")
     print(f"CHA problems: {len(probs)}   metric: halvings per evaluation "
           f"= log2(w0/xtol)/nfev  (bisection = 1.0)\n")
     print(f"{'problem':<16} {'CH nfev':>8} {'CH h/ev':>8} {'gate ok%':>9} "
@@ -119,7 +120,8 @@ def main():
 
         stats = {}
         x_o, n_o, ok_o = pure_root(f, a, b, XTOL, MAXFEV, similarity="ratio",
-                                   scale="derived3", guard="credit", stats=stats)
+                                   scale="derived3", guard="credit", stats=stats,
+                                   prestep=prestep)
         forced = 100.0 * stats.get("forced", 0) / max(n_o, 1)
 
         ch_h = decades / n_ref if n_ref else float("nan")
@@ -146,4 +148,5 @@ def main():
 
 
 if __name__ == "__main__":
-    main()
+    import sys
+    main("progress" if "--gate" in sys.argv else "none")