pre-step gate: prestep='none'|'progress' (default bit-identical), refuse the similarity step BEFORE spending an evaluation when it promises less progress than bisection — two lengths already in hand, no new constant; R1-R4 pinned by tests/test_prestep_gate.py (6 green); the gate grid writes to its OWN sweep_gate.json

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

sweep_full.py

@@ -110,19 +110,23 @@ def make_method(spec):
         return BASELINES[spec[1]]
     sim, scale, guard = spec[1], spec[2], spec[3]
     space = spec[4] if len(spec) > 4 else "x"
+    prestep = spec[5] if len(spec) > 5 else "none"
 
     def m(f, a, b, xtol, maxfev):
         return pure_root(f, a, b, xtol, maxfev, similarity=sim,
-                         scale=scale, guard=guard, space=space)
+                         scale=scale, guard=guard, space=space, prestep=prestep)
     return m
 
 
 def label(spec):
     if spec[0] == "base":
         return spec[1]
+    tag = "pure"
     if len(spec) > 4 and spec[4] != "x":
-        return f"{spec[4]}.{spec[1]}.{spec[2]}.{spec[3]}"
-    return f"pure.{spec[1]}.{spec[2]}.{spec[3]}"
+        tag = spec[4]
+    if len(spec) > 5 and spec[5] != "none":
+        tag = f"{tag}+gate" if tag != "pure" else "gate"
+    return f"{tag}.{spec[1]}.{spec[2]}.{spec[3]}"
 
 
 def evaluate(spec):
@@ -185,6 +189,15 @@ def build_grid_log(smoke):
             for sim in sims for sc in ("derived", "derived3") for gu in guards]
 
 
+def build_grid_gate(smoke):
+    """The pre-step gate grid (PREREG 2026-09-21): the published x-space step with the
+    gate switched on. Baselines are not recomputed - they are already in sweep_full.json."""
+    sims = ["ratio", "sqrt"] if smoke else sorted(PURE_SIMS)
+    guards = ("credit", "safe") if smoke else GUARD_MODES
+    return [("pure", sim, sc, gu, "x", "progress")
+            for sim in sims for sc in ("derived", "derived3") for gu in guards]
+
+
 def build_grid(smoke):
     specs = [("base", nm) for nm in BASELINES]
     sims = sorted(PURE_SIMS)
@@ -205,7 +218,9 @@ def build_grid(smoke):
 def main():
     smoke = "--smoke" in sys.argv
     logmode = "--log" in sys.argv          # the u-space grid, written to its OWN file
-    specs = build_grid_log(smoke) if logmode else build_grid(smoke)
+    gatemode = "--gate" in sys.argv        # the pre-step gate grid, likewise
+    specs = (build_grid_gate(smoke) if gatemode else
+             build_grid_log(smoke) if logmode else build_grid(smoke))
     t0 = time.time()
     print(f"sweep: {len(specs)} configurations x 199 problems "
           f"({'SMOKE' if smoke else 'FULL'}{', LOG-SPACE' if logmode else ''})", flush=True)
@@ -221,6 +236,16 @@ def main():
 
     # the published sweep_full.json is what verify_article.py checks the paper
     # against, so the log grid never writes into it
+    if gatemode:
+        # never into sweep_full.json: that file is what verify_article.py checks the
+        # paper against, and the smoke run of 2026-09-21 did land in sweep_smoke.json
+        # before this branch existed
+        out = "sweep_gate_smoke.json" if smoke else "sweep_gate.json"
+        with open(out, "w", encoding="utf8") as fh:
+            json.dump(results, fh)
+        print(f"\nwrote {out}  ({time.time() - t0:.0f}s total)\n", flush=True)
+        report(results)
+        return
     out = ("sweep_log_smoke.json" if smoke else "sweep_log.json") if logmode else \
           ("sweep_smoke.json" if smoke else "sweep_full.json")
     with open(out, "w", encoding="utf8") as fh: