unreal: parallel sign-edge repair + cheap SW route prefilter (L94); SW startup 2.75 -> 0.43 s

- Unreal requests Core's deterministic parallel sign-edge repair (UE ParallelFor, capped at
  10 workers); headless defaults to parallel (--serial-sign-edge-repair for A/B). SW
  sign_edge_distances 1,942 -> 37 ms, ShapeStage 2,156 -> 198 ms.
- SW fallback route planner checks the exact mouth-radius endpoint constraints before sampling
  terrain (58,480 of 78,408 candidates skip heightfield work); same 35 eligible, same chosen route.
  SerializeResolvedWorld 468 -> 115 ms; BeginPlay block 0.58 -> 0.22 s.
- Unreal SW: first admission 2.75 -> 0.43 s, LOD0-2 settled 5.20 -> 2.81 s; FI 3.40 -> 3.12 s.
- World identical: assembly/recipe/plan hashes unchanged; serial vs parallel per-tile hashes equal.
  Fast tier PASS; Linux UE host builds.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016dhxM43dnWvUu2B5Ph1iG1

Standalone/Source/StreamBenchmarkHeadless.cpp

@@ -53,8 +53,7 @@ namespace
         bool Linux77Profile=false;
         bool ExactMidpointDensityMemo=false;
         bool ActiveLaneBatching=false;
-        bool ParallelSignEdgeRepair=false;
-        bool HasSignEdgeRepairOverride=false;
+        bool ParallelSignEdgeRepair=true;
         int ProofBlockCells=8;
         int ShapeHelperLimit=8;
         bool AuditBasePageEquivalence=false;
@@ -1523,9 +1522,9 @@ namespace
             else if(arg=="--exact-midpoint-density-memo")options.ExactMidpointDensityMemo=true;
             else if(arg=="--active-lane-batching")options.ActiveLaneBatching=true;
             else if(arg=="--parallel-sign-edge-repair")
-            {options.ParallelSignEdgeRepair=true;options.HasSignEdgeRepairOverride=true;}
+            {options.ParallelSignEdgeRepair=true;}
             else if(arg=="--serial-sign-edge-repair")
-            {options.ParallelSignEdgeRepair=false;options.HasSignEdgeRepairOverride=true;}
+            {options.ParallelSignEdgeRepair=false;}
             else if(arg.starts_with("--proof-block-cells="))
             {
                 if(!readInt("--proof-block-cells=",options.ProofBlockCells)
@@ -2275,8 +2274,7 @@ int main(int argc,char** argv)
         options.AuditOreVeinYield,options.AuditNativeCaves,options.InstrumentTileDrain,
         options.AuditMotifIntervals,
         options.ExactMidpointDensityMemo,options.ActiveLaneBatching,
-        options.ProofBlockCells,options.HasSignEdgeRepairOverride
-            ?options.ParallelSignEdgeRepair:options.FloatingIslandsRecipe,
+        options.ProofBlockCells,options.ParallelSignEdgeRepair,
         options.AuditNativeLattice,options.LatticeOrphanControl,
         options.CaptureSkipWalkability,options.ProfilePassageComposer,
         options.StreamHashAllowUniformSkips,options.Linux77Profile,