feat(passages): §6.5 landings -- you arrive somewhere you can stand

The last unbuilt Tier 1 item. A passage was a bore through rock with no
floor inside the walkable angle, so its mouth was not a standing position
and neither was anything near it -- the departure mouth measured a FOUR-CELL
player-fit component. You arrived and there was nowhere to stand.

Both ends of all 7 passages now open into a landing, sized from the body:
  capsule diameter 2.72 vox      floor >= 12 vox (3 m) to stand and turn
  capsule height 7.04 vox        room >= 12 vox tall, stock mouth gives 18 (4.5 m)
  3-voxel floor slab, tube tangent to it -- no lip to climb out of
  connector 5-vox radius: 2.5 m clear width, 3 m clear height
  ramps over 44 deg get a deterministic level dog-leg

⭐ THE MOUTHS ARE NO LONGER SPECKS:
  archetype        components      largest      arrival-departure
  Maze             309 -> 340      176 -> 3210    43-81  -> 3210-3210
  TunnelNetwork    467 -> 227     1292 -> 3841     2-1   -> 3841-269
  Underwater        86 -> 117       35 -> 3838     3-11  -> 3838-267
  FlatPlain         45 ->  11      259 -> 2130     1-1   ->  268-273
  CrystalChamber   197 ->  90       24 ->  286     1-1   ->  286-274
  FloatingIslands    2 ->   1        3 ->   72     1-1   ->   72-72

Law 1/8 -> 2/7 connected (1 refused on MaxCells), and critically ZERO
connections now run through a four-cell pocket.

Every landing floor was verified against the FINAL density, after all posts:
14/14 pass the 44 deg slope bracket, worst room gradient .059, worst
connector .522. 14/14 deterministic root joins. 0 seal failures.
0 box-verdict violations across 82 proved + 174 mixed, 109,142 voxels.
Op-stack bit-identical, order-independence green over 10 slots / 31
passages / 3 pool orders. Cache 0.665 us rebuild, 0.646 us hot.

Post order: origin spine -> vertical seal -> passage tube + landing floor
-> XY edge seal. Landings clamp 4 voxels inside the vertical seal; the XY
seal stays last and wins at world edges.

⚠️ ARCHITECTURAL NOTE, not a detail: landings join a deterministic annular
ROOT HUB at (0,0), built identically for every endpoint -- no nearest-
component search, no passage ordering. That is what makes the join
guaranteed rather than likely, and it extends the (0,0) spine concept from
a landmark into a structural network. It also means routes tend to pass
through the centre, which is a gameplay consequence worth Jahni's eye.

⚠️ AND IT DOES NOT CLOSE THE LAW. Codex is explicit: the landings guarantee
membership in the new root network, NOT in the archetype's pre-existing fit
component. The whole-strate Maze check still shows a 71.9-voxel gap between
1,235 and 2,938-cell components. So the native corridor networks remain
disconnected from the root network in places. Real, separate, next.

52 build-and-measure cycles, ~9 hours, finding real geometry bugs on the
way (a landing floor overlapping the ramp cells and hiding a floor
discontinuity; the disturbance pass refilling connector headroom).

Build clean, 32/32 success, 0 failed. Showcase regenerated.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01K8V9my1PL68pmQb2gutZZV

Source/VoxelForge/Private/VoxelDensityOpStack.cpp

@@ -1854,8 +1854,7 @@ namespace
         void Eval(float X, float Y, float Z, FVoxelOpSample& InOut) const override
         {
             if (!Manager) { return; }
-            const float ModSDF = Manager->EvaluateModifierSDF(X, Y, Z);
-            VF_ApplyPassageCarving(InOut.Density, ModSDF, Base, Seal);
+            Manager->ApplyPassageModifier(InOut.Density, X, Y, Z, Base, Seal);
         }
 
         // ≡ la garde `AnyPassageNearBox` écrite à la main dans ClassifyTile — déjà écrite, ici
@@ -1863,6 +1862,12 @@ namespace
         EVoxelOpEffect EffectOverBox(const FBox& VoxelBox, const FVoxelOpContext&) const override
         {
             if (!Manager) { return EVoxelOpEffect::Identity; }
+            if (Manager->AnyPassageLandingFloorNearBox(VoxelBox.Min, VoxelBox.Max))
+            {
+                // The room carves air, while its support slab force-writes solid. Both
+                // hypotheses must therefore be killed for a box touching that slab.
+                return EVoxelOpEffect::Both;
+            }
             return Manager->AnyPassageNearBox(VoxelBox.Min, VoxelBox.Max)
                  ? EVoxelOpEffect::CarveOnly : EVoxelOpEffect::Identity;
         }
@@ -5207,10 +5212,10 @@ void FVoxelOpStack::AppendStructuralPost(float StrateTopWorldZ, float StrateBott
                                          const UVoxelStrateManager* StrateManager)
 {
     // ORDRE NON NÉGOCIABLE : la spine creuse l'intérieur (et ne touche JAMAIS les bandes de seal),
-    // le seal vertical re-solidifie ses bandes, les passages percent les seals, puis la limite XY
-    // gagne sur tout ce qui précède. Ainsi, même un passage placé dans la rampe ou au-delà du rayon
-    // ne peut pas ouvrir la coque extérieure. Les éditions joueur restent le dernier post de
-    // GetDensityAt, hors de cette pile, comme avant.
+    // le seal vertical re-solidifie ses bandes, les passages (tube + landing + support) percent
+    // les seals, puis la limite XY gagne sur tout ce qui précède. Ainsi, même un passage placé
+    // dans la rampe ou au-delà du rayon ne peut pas ouvrir la coque extérieure. Les éditions joueur
+    // restent le dernier post de GetDensityAt, hors de cette pile, comme avant.
     Add(MakeUnique<FOriginSpineOp>(StrateTopWorldZ, StrateBottomWorldZ, SealThickness, BaseDensity, SpineRadius));
     Add(MakeUnique<FBoundarySealOp>(StrateTopWorldZ, StrateBottomWorldZ, SealThickness, BaseDensity));
     Add(MakeUnique<FPassageCarveOp>(StrateManager, BaseDensity, SealThickness));