rugnux: carry the point-group promotion into the second pass

The two-pass rotation run reinstates pass-1's space group for pass 2's merge, so
pass 2 skips the search block entirely - and with it the flag that records that
the Laue class was CHOSEN by the search rather than given. The canonical output
therefore printed the plain "no twinning: the Laue class is holohedral, so no
merohedral twin law exists", which is exactly the circular conclusion the flag
was added to replace; only the throwaway _01 output carried the caveat.

The text is written per pass, inside RunPipeline, so the flag has to travel with
prepass_merge_sg_ rather than being patched onto the returned result.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

rugnux/Rugnux.cpp

@@ -235,6 +235,7 @@ ProcessResult Rugnux::Run(RugnuxObserver *observer) {
         force_rotation_result_.reset();
         prepass_sg_reindexed_ = false;
         prepass_merge_sg_.reset();
+        prepass_promoted_point_group_ = false;
 
         logger.Info("Rotation two-pass geometry post-refinement: first pass (header geometry) -> {}_01_*",
                     base_prefix);
@@ -258,6 +259,7 @@ ProcessResult Rugnux::Run(RugnuxObserver *observer) {
         // setting the de-novo primitive frame does not share, which is left to re-search.
         experiment_.SpaceGroupNumber(std::nullopt);
         prepass_merge_sg_ = prepass_sg_reindexed_ ? std::nullopt : pass1.space_group_number;
+        prepass_promoted_point_group_ = pass1.twinning.laue_class_was_chosen_by_promotion;
 
         logger.Info("Rotation two-pass geometry post-refinement: second pass (refined geometry, canonical) -> {}_*",
                     base_prefix);
@@ -1206,7 +1208,9 @@ ProcessResult Rugnux::RunPipeline(RugnuxObserver *observer, bool write_output, b
         // True when the point group below was chosen BY THE SEARCH (rather than given by the user) and is
         // above triclinic - i.e. a promotion was made, which is what makes a later "the Laue class is
         // holohedral so there is no twin law" conclusion circular.
-        bool promoted_point_group = false;
+        // Pass 2 reuses pass-1's group instead of searching, so the promotion it needs to report was
+        // made there; a first / single pass has no carried-over group and decides this below.
+        bool promoted_point_group = prepass_merge_sg_.has_value() && prepass_promoted_point_group_;
         if (!experiment_.GetGemmiSpaceGroup().has_value()) {
             SearchSpaceGroupOptions sg_opts;
             sg_opts.merge_friedel = experiment_.GetScalingSettings().GetMergeFriedel();

rugnux/Rugnux.h

@@ -179,6 +179,12 @@ class Rugnux {
     // the second pass, and for a reindex-derived group (left to re-search).
     std::optional<int64_t> prepass_merge_sg_;
 
+    // Whether the group in prepass_merge_sg_ was PROMOTED by pass-1's search rather than given. Pass 2
+    // reuses the group without searching, so it cannot work this out for itself - and without it the
+    // canonical output reports "the Laue class is holohedral, so no twin law exists" about a Laue class
+    // the search chose, which is the circular claim that reasoning exists to flag.
+    bool prepass_promoted_point_group_ = false;
+
     // Stills global geometry-refinement first pass (config_.refine_geometry): index a spread sample of
     // frames, bundle-adjust the shared beam/distance/cell from the strongest ones, and apply the result
     // to experiment_ so the main pass re-indexes with it. No-op (leaves experiment_ unchanged) if it