planner: four-strate owner plan spawns (L66); pinned 2-strate regression fixture

- Core caps each passage mouth reach to its own strate's usable content band (owner
  DA_Strate1 exports ReachMax=5000 owner voxels, which put the SW->FI lower mouth 79.5 m
  below FI, inside TN).
- Unreal adapter: SW route search keeps the old 64 m candidates first, then a bounded
  single-mouth search with shorter lengths; logs candidate/rejection counts.
- Internal-chain passage floor/support tweaks (only with >2 strates): ripple 1-2 4.78->2.90 cm,
  2-3 3.57->0.10 cm. Interfaces still 0/3 walkable (59/3/2 unsupported).
- verify.py: legacy tiers use Standalone/data/regression/owner_world_2strate_l61.json; new
  four-strate stage reads its expectations from owner_world.json (currently red on interfaces).
- Unreal trace L14 vs HEAD, same assets (16-chunk FlatPlain): 12.20 vs 12.56 worker-s; no x2.

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

Standalone/Core/src/ShapeWorldInternal.h

@@ -1045,6 +1045,7 @@ public:
         {
             const auto& passage=ResolvedLayout->passages[passageIndex];
             if(passage.controlPoints.size()<2)continue;
+            const bool internalChainPassage=passageIndex>0;
             const auto supportStratum=[&](std::int32_t strateIndex)
                 ->const VoxelForgeCore::ResolvedLayoutStratumV2*
             {
@@ -1490,7 +1491,7 @@ public:
                 // the nominal height smoothly as a tread approaches its landing.
                 double floorOffset=bridgeDeck
                     ?PassageBridgeDeckOffsetMetres(passageIndex,static_cast<std::size_t>(index))
-                    :std::lerp(0.15,0.20,lowerMouthBlend);
+                    :std::lerp(internalChainPassage?0.20:0.15,0.20,lowerMouthBlend);
                 const double horizontalLengthSq=dx*dx+dy*dy;
                 const bool overlapSupportJoin=index+12<lastIndex
                     &&!IsPassageShortSpanSegment(passageIndex,static_cast<std::size_t>(index))
@@ -1524,7 +1525,7 @@ public:
                             +(2.0*v0-5.0*v1+4.0*v2-v3)*t2
                             +(-v0+3.0*v1-3.0*v2+v3)*t3);
                     };
-                    constexpr double SmoothSupportHeightWeight=0.25;
+                    const double SmoothSupportHeightWeight=internalChainPassage?0.0:0.25;
                     centerZ+=(interpolate(p0.positionSubvoxels[2],segmentA.positionSubvoxels[2],
                         segmentB.positionSubvoxels[2],p3.positionSubvoxels[2])-centerZ)
                         *SmoothSupportHeightWeight;
@@ -1576,12 +1577,14 @@ public:
                 // Keep the supported ramp to a comfortable walking width. Extending a
                 // full bore-radius shelf across overlapping helix coils can block the
                 // capsule on the neighbouring turn.
-                const bool lowerMouthBodyOverlap=index>=lowerMouthIndex-2
+                const bool lowerMouthBodyOverlap=ResolvedLayout->strates.size()>2
+                    &&index>=lowerMouthIndex-2
                     &&supportQueryDepth<0.98*qPerMetre;
                 // Keep a narrow walk core, but place its top on the native surface
                 // so the support remains a worn ramp instead of a route-height slab.
-                const bool mouthTread=entryMouthShoulder
-                    &&(!floatingIslandPassage||passage.style==0);
+                const bool mouthTread=lowerMouthBodyOverlap
+                    ||(entryMouthShoulder
+                        &&(!floatingIslandPassage||passage.style==0||internalChainPassage));
                 double distanceFromMouthMetres=std::numeric_limits<double>::infinity();
                 if(entryMouthShoulder)
                 {
@@ -1656,7 +1659,8 @@ public:
                     *(3.0-2.0*supportEdgeT);
                 const double mouthSupportThicknessVoxels=std::lerp(
                     0.35*supportThicknessVoxels,supportThicknessVoxels,mouthSupportT);
-                const double localSupportThicknessVoxels=entryMouthShoulder
+                const double localSupportThicknessVoxels=(entryMouthShoulder
+                    ||lowerMouthBodyOverlap)
                     ?mouthSupportThicknessVoxels*(1.0-0.72*supportEdgeSmooth)
                     :supportThicknessVoxels;
                 double mouthSupportBlend=1.0;
@@ -1668,8 +1672,8 @@ public:
                         *(3.0-2.0*mouthBlendT);
                 }
                 const double supportEdgeDepth=mouthTread?0.25:0.35;
-                const double mouthFloorOffset=mouthTread
-                    ?std::lerp(0.15,0.19,lowerMouthBlend):floorOffset;
+                const double mouthFloorOffset=internalChainPassage?0.20
+                    :mouthTread?std::lerp(0.15,0.19,lowerMouthBlend):floorOffset;
                 const double baseFloorQ=centerZ-radius+mouthFloorOffset*qPerMetre
                     -supportEdgeSmooth*supportEdgeDepth*qPerMetre;
                 const double nativeSurfaceQ=static_cast<double>(qz)
@@ -1678,7 +1682,8 @@ public:
                 // blends the source field directly instead of extending this SDF top.
                 const double nativeFieldOffset=std::clamp(nativeSurfaceQ-baseFloorQ,
                     -0.80*qPerMetre,0.80*qPerMetre);
-                const double nativeSurfaceBlend=mouthTread?1.0:1.0-mouthReliefT;
+                const double nativeSurfaceBlend=mouthTread
+                    ?internalChainPassage?0.0:1.0:1.0-mouthReliefT;
                 const double nativeTreadOffset=std::clamp(
                     nativeFieldOffset*nativeSurfaceBlend+floorReliefOffset
                         -std::abs(treadRelief)*0.08*qPerMetre