wip(assembler): round L37 -- FI mouth carve-fade fix, no raised bridge (style 0); research R1

The passage mouth fade multiplied the signed carve distance by zero, which turned native rock into an
open surface (the reason earlier rounds stamped walk pads at mouths); it now blends between the
uncarved field and the full signed carve. The FI style-0 route followed a lifted grade envelope over
the crater (the "bridge"); it now runs on the rim and follows the native surface. New built-shape and
crease audits with thresholds frozen before the fix (L36 and box controls fail). 24/24 passage rows,
30/30 determinism, 16/16 invariants, 18/18 interface/ring. Unreal: one recipe setter (uncompiled).
Research R1 (read-only, web): ranked proposals for natural walkable mouths, floor-limited carve first.

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

Standalone/Core/src/FloatingIslandsInternal.h

@@ -203,6 +203,7 @@ namespace floating_island_detail
         HashWord(hash, static_cast<std::uint64_t>(recipe.boundarySealSubvoxels), 8);
         HashWord(hash, static_cast<std::uint64_t>(recipe.bridgeHalfWidthSubvoxels), 8);
         HashWord(hash, static_cast<std::uint64_t>(recipe.bridgeThicknessSubvoxels), 8);
+        if(recipe.terrainFollowingRoute)HashWord(hash,1,1);
         HashWord(hash, HashRouteConstraints(recipe.routeConstraints), 8);
         return hash;
     }
@@ -805,9 +806,39 @@ namespace floating_island_detail
         const double t = std::clamp(along / length, 0.0, 1.0);
         if (alongFraction) *alongFraction = t;
         const double deck = az + (static_cast<double>(edge.endSubvoxels[2]) - az) * t;
+        const std::uint64_t westernEdgeId = StableId(recipe.seed, 0x200000000ull,
+            0x425249444745ull);
+        const bool westernSupportConnector=edge.stableId==westernEdgeId;
+        if(recipe.geometryVersion>=2&&WorldAssemblyEvaluatorVersion>=183
+            &&westernSupportConnector)
+        {
+            const double phase=static_cast<double>(Roll(recipe.seed,edge.stableId,0x5749445448ull)
+                &0xffffffffull)*(2.0*Pi/4294967296.0);
+            const double localHalfWidth=std::max(
+                static_cast<double>(recipe.routeConstraints.capsuleRadiusSubvoxels+Q),
+                static_cast<double>(edge.halfWidthSubvoxels)
+                    +0.48*static_cast<double>(Q)*std::sin(6.0*Pi*t+phase));
+            const double localThickness=static_cast<double>(edge.thicknessSubvoxels);
+            const double rounding=std::min({1.5*static_cast<double>(Q),
+                localHalfWidth*0.6,localThickness*0.45});
+            const double roundedX=side-(localHalfWidth-rounding);
+            const double roundedY=std::abs(along-0.5*length)-(0.5*length-rounding);
+            const double roundedZ=std::abs(z-(deck-0.5*localThickness))
+                -(0.5*localThickness-rounding);
+            const double roundedOutside=std::sqrt(
+                std::pow(std::max(roundedX,0.0),2)
+                +std::pow(std::max(roundedY,0.0),2)
+                +std::pow(std::max(roundedZ,0.0),2));
+            const double roundedInside=std::min(std::max(roundedX,
+                std::max(roundedY,roundedZ)),0.0);
+            if(topSurface)*topSurface=z-deck>=std::max(horizontal,
+                deck-localThickness-z);
+            return roundedOutside+roundedInside-rounding;
+        }
         const double arch = recipe.geometryVersion >= 2
-            ? 2.0 * static_cast<double>(edge.thicknessSubvoxels) * (4.0 * t * (1.0 - t))
-            : 0.0;
+                && WorldAssemblyEvaluatorVersion < 172
+                ? 2.0 * static_cast<double>(edge.thicknessSubvoxels) * (4.0 * t * (1.0 - t))
+                : 0.0;
         const double upper = z - deck;
         const double lower = deck - static_cast<double>(edge.thicknessSubvoxels) - arch - z;
         if (topSurface) *topSurface = upper >= std::max(horizontal, lower);
@@ -1174,8 +1205,8 @@ namespace floating_island_detail
         // Land each connector well inside the broad top so the full capsule footprint remains
         // supported across the bridge-to-island transition, including bounded surface roughness.
         // Les connecteurs recouvrent le plateau pour soutenir toute la capsule au raccord.
-        // Keep the narrow span exposed to open sky; a smaller fraction buries most of it in the island tops.
-        // Garder la passerelle etroite visible dans le vide ; une fraction plus faible l'enfouit dans les plateaux.
+        // Keep the capsule footprint supported while seating L37 connectors just below the native island tops.
+        // Garder l'appui de la capsule tout en enfouissant les connecteurs L37 juste sous les plateaux.
         const double landingFraction = recipe.geometryVersion >= 2 ? 0.52 : 0.62;
         const double fromReach = static_cast<double>(from.radiusSubvoxels) * landingFraction;
         const double toReach = static_cast<double>(to.radiusSubvoxels) * landingFraction;
@@ -1183,7 +1214,19 @@ namespace floating_island_detail
         const double sy = from.centerSubvoxels[1] + uy * fromReach;
         const double ex = to.centerSubvoxels[0] - ux * toReach;
         const double ey = to.centerSubvoxels[1] - uy * toReach;
-        const double routeDeckLift = recipe.geometryVersion >= 2 ? 1.0 * Q : 0.0;
+        const bool craterMouthConnector=WorldAssemblyEvaluatorVersion>=174
+            &&(from.ordinal==recipe.anchorIslandOrdinal
+                ||to.ordinal==recipe.anchorIslandOrdinal);
+        const bool westernSupportConnector=WorldAssemblyEvaluatorVersion>=178
+            &&((from.ordinal==0&&to.ordinal==1)||(from.ordinal==1&&to.ordinal==0));
+        const double routeDeckLift=recipe.geometryVersion>=2
+            ?(WorldAssemblyEvaluatorVersion>=178
+                ?(westernSupportConnector
+                    ?(WorldAssemblyEvaluatorVersion>=181?-1.0
+                        :(WorldAssemblyEvaluatorVersion>=180?-1.25
+                            :(WorldAssemblyEvaluatorVersion>=179?-1.5:-1.0))):-2.0)
+                :(craterMouthConnector?-2.0
+                    :(WorldAssemblyEvaluatorVersion>=172?-1.0:1.0)))*Q:0.0;
         const double sz = IslandTopSurface(recipe, from, sx, sy) + routeDeckLift;
         const double ez = IslandTopSurface(recipe, to, ex, ey) + routeDeckLift;
         edge.startSubvoxels = {RoundQ(sx), RoundQ(sy), RoundQ(sz)};
@@ -1336,6 +1379,7 @@ std::optional<FloatingIslandManifestV1> FloatingIslandManifestV1::FromJson(
                 manifest.recipe.anchorMouthOffsetSubvoxels))
         {error="floating-island geometry version 7 is missing a passage-rooted anchor field";return std::nullopt;}
     }
+    manifest.recipe.terrainFollowingRoute=recipeValue.Get("terrain_following_route").Boolean(false);
     if (!floating_island_detail::ReadU32(root.Get("schema_version"), schema)
         || !floating_island_detail::ReadHash(root.Get("content_hash"), manifestHash)
         || !floating_island_detail::ReadU32(recipeValue.Get("schema_version"), manifest.recipe.schemaVersion)
@@ -1495,6 +1539,7 @@ std::string FloatingIslandManifestV1::ToJson() const
             << ",\"anchor_island_minimum_radius_q\":" << recipe.anchorIslandMinimumRadiusSubvoxels
             << ",\"anchor_root_bottom_z_q\":" << recipe.anchorRootBottomZSubvoxels
             << ",\"anchor_mouth_offset_q\":" << recipe.anchorMouthOffsetSubvoxels;
+    if(recipe.terrainFollowingRoute)out << ",\"terrain_following_route\":true";
     out << ",\"blend_radius_q\":" << recipe.blendRadiusSubvoxels
         << ",\"contour_warp_q\":" << recipe.contourWarpSubvoxels
         << ",\"roughness_q\":" << recipe.roughnessSubvoxels
@@ -1746,6 +1791,26 @@ std::optional<FloatingIslandManifestV1> PlanFloatingIslandCluster(
             const std::int64_t y = floating_island_detail::RoundQ(
                 static_cast<double>(a.centerSubvoxels[1]) + dy * t);
             std::int64_t routeX=x,routeY=y;
+            if(WorldAssemblyEvaluatorVersion>=192&&recipe.terrainFollowingRoute
+                &&recipe.geometryVersion>=5
+                &&segment+2==count&&pieces>1)
+            {
+                const auto& anchor=islands[recipe.anchorIslandOrdinal];
+                const std::uint32_t side=static_cast<std::uint32_t>(
+                    floating_island_detail::UnitQ16(recipe.seed,anchor.stableId,
+                        0x414e43484f524d50ull)&1u);
+                const double length=std::hypot(dx,dy);
+                const double bend=10.0*floating_island_detail::Q
+                    *std::pow(std::sin(floating_island_detail::Pi*t),2.0);
+                const double sign=side?-1.0:1.0;
+                if(length>0.0)
+                {
+                    routeX=floating_island_detail::RoundQ(
+                        static_cast<double>(routeX)+sign*(-dy/length)*bend);
+                    routeY=floating_island_detail::RoundQ(
+                        static_cast<double>(routeY)+sign*(dx/length)*bend);
+                }
+            }
             if(recipe.geometryVersion>=5&&segment+2==count&&piece==pieces)
             {
                 const auto& anchor=islands[recipe.anchorIslandOrdinal];
@@ -1762,8 +1827,11 @@ std::optional<FloatingIslandManifestV1> PlanFloatingIslandCluster(
                 routeX=floating_island_detail::RoundQ(mouthX);
                 routeY=floating_island_detail::RoundQ(mouthY);
             }
-            const auto surface = floating_island_detail::FindCapsuleFootingTopZ(
-                recipe, manifest.plan, routeX, routeY);
+            const auto surface = WorldAssemblyEvaluatorVersion>=199
+                &&recipe.terrainFollowingRoute
+                ?floating_island_detail::FindSurfaceZ(recipe,manifest.plan,routeX,routeY)
+                :floating_island_detail::FindCapsuleFootingTopZ(
+                    recipe,manifest.plan,routeX,routeY);
             if (!surface)
             { error = "island planner could not find a full capsule-width support surface along its connector chain"; return std::nullopt; }
             WorldAssemblyRoutePointV1 point;