Carry the twin-immune zone verdict as a value, not as report text

The report decided whether to name a twin law by substring-matching
ProcessResult::twin_zone_decision, a field every zone read overwrites.
A run reads the zone up to four times, so the match saw the last
comparison made rather than the refusal that stood, and TWIN_LAW and the
_pdbx_reflns_twin mmCIF loop could appear on a crystal whose refusal was
overturned - or be missing on one whose refusal stood.

TwinZoneVerdict already returns the verdict; it now records it on the
result, and the decision point reads that.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_013nW6FNRP1bBJJ8pfHiByAT

rugnux/Rugnux.cpp

@@ -1785,6 +1785,11 @@ namespace {
                 z.tncs_normalised ? ", normalised per pseudo-translation class" : "",
                 verdict < 0 ? "acentric, the added operators are a twin law or a pseudo-symmetry"
                 : verdict > 0 ? "centric, the added operators are real" : "undecided");
+        // The verdict as a VALUE, for the report to act on. Every caller acts on a decisive read -
+        // the refusal stands or it is overturned - so recording it here records the decision, where
+        // matching on the text records only the last comparison the run happened to make.
+        if (verdict != 0)
+            result.twin_zone_refusal_stood = verdict < 0;
         return verdict;
     }
 
@@ -6924,7 +6929,7 @@ ProcessResult Rugnux::RunPipeline(RugnuxObserver *observer, bool write_output, b
             // refused group adds, at the fraction its own disagreement implies (a lower bound).
             if (twin_sg && result.space_group_search
                 && result.space_group_search->refused_point_group_representative
-                && result.twin_zone_decision.find("acentric, the added") != std::string::npos) {
+                && result.twin_zone_refusal_stood) {
                 const auto &sgs = *result.space_group_search;
                 const gemmi::GroupOps hi = sgs.refused_point_group_representative->operations();
                 const gemmi::GroupOps lo = twin_sg->operations();

rugnux/Rugnux.h

@@ -364,6 +364,12 @@ struct ProcessResult {
     // The twin-immune zone read for a promotion a twin gate refused (the H ratio or the added-operator
     // R), and what was decided on it. Empty when no twin gate fired.
     std::string twin_zone_decision;
+    // What that zone DECIDED, carried as a value beside the text: true where the refusal STOOD (the
+    // added operators read acentric and are recorded as a twin law), false where the zone overturned
+    // the refusal or decided nothing. A run reads the zone up to four times and each read rewrites
+    // the text, so the decision cannot be recovered from the text - matching on it named the twin law
+    // of whichever comparison happened to be made last rather than of the refusal that stood.
+    bool twin_zone_refusal_stood = false;
     // Per lattice twin law outside the adopted group: the operator's own H, the fraction it implies
     // and its correlation, on the final merge. Report-only.
     std::vector<std::string> twin_law_evidence;