feat(descent): landing ROOMS and a walkable tunnel -- per Jahni's correction

Jahni corrected the design: "the connection between level is a tiny tunnel
connecting both strate, not vertical, it needs to be walkable" and "'the
spine' shouldn't be carved except optionally from the top first strate,
then it's used to have a landing room".

COMPOSER-NOTES §6.8 had said the spine "provides a clean landing space, not
a continuous open shaft" -- and the implementation carved a vertical
cylinder anyway. A vertical cylinder has no walkable floor except at its
bottom, so a carve guaranteeing open AIR guaranteed nothing STANDABLE.
That one omission is behind five of my dead hypotheses this week.

Now:
  origin spine   a finite rounded ROOM per strate, no vertical bore.
                 radius 14 -> 8 m wide, 7.5 m tall
  descent        a walkable tunnel, single-file by design: 3 m mouth,
                 2.5 m waist, gradient capped at a NAMED 15 deg
  exotic styles  VerticalShaft / SpiralDescent / CascadingDrops /
                 CrackCrevice preserved, no longer the default

⚠️ THE GEOMETRY BITES, and it is worth Jahni's eye: at 15 deg a 32 m drop
needs 119.4 m of horizontal run -- about 59.7 m per switchback leg. That is
a long walk between strates. It is the honest consequence of "walkable",
not a tuning artifact, and the alternative is a steeper number.

⭐ AND THE ROOT CAUSE GOT NAMED A THIRD TIME, by Codex mid-run: "the round
tube was hollow air but had no authored support strip, so 'open' still did
not mean 'standable'." Tunnels now carry a floor band, and the root join
terminates in the finite origin room rather than an annular shaft hub.

Measured, commandlet sweep, 8 archetypes x 8 seeds, 64/64 valid:
  origin column has player-fit cells   17/64 -> 63/64
  origin column reachable               0/64 ->  7/64
  arrival landing probes            315/320 fit AND in the arrival component
  tunnel audit    5,916/5,916 floor and capsule samples pass; zero gradient,
                  floor, capsule, geometry or seal failures
  narrow-gap events 0        box verdicts 14 checked, 0 violations

⚠️ arrival->departure is 6/64. The landings and tunnels are now provably
walkable; what remains is the INTRA-STRATE vertical connectivity problem
found in 6b91669 -- floors at different levels inside a strate with nothing
joining them. Separate and larger. Not tuned toward.

⚠️ PROCESS: this took 5.7 hours, of which Codex used 4 SECONDS of CPU. The
rest was polling the 73-minute automation suite at ~10% machine load. The
commandlet exists to avoid exactly that. New rule recorded: iterate with the
commandlet, full suite ONCE at the end.

Editor + Shipping builds clean. Automation 32/32, 0 failed.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_012aheo2crrZmHuYtPpdY2Cb

Source/VoxelForge/Private/Tests/VoxelForgePassageOpenSpaceTest.cpp

@@ -10,6 +10,7 @@
 #include "VoxelCaveMorphology.h"
 #include "VoxelDensityPrimitives.h"
 #include "VoxelForgeTestFixture.h"
+#include "VoxelPassageGeometry.h"
 
 IMPLEMENT_SIMPLE_AUTOMATION_TEST(
     FVoxelForgePassageLandsInOpenSpaceTest,
@@ -89,6 +90,366 @@ namespace
             return 0.0f;
         }
     }
+
+    bool FindFinalDensityFloor(
+        const UVoxelGenerator& Generator,
+        const FVector& Centreline,
+        float ExpectedFloorZ,
+        float& OutFloorZ)
+    {
+        constexpr float SampleStep = 0.25f;
+        const float ExpectedAt = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, ExpectedFloorZ);
+        const float ExpectedBelow = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, ExpectedFloorZ - 0.75f);
+        const float ExpectedAbove = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, ExpectedFloorZ + 0.75f);
+        // Search around the authored tunnel floor, not from an arbitrary lower surface. A source
+        // archetype may contain another cave floor below the tunnel; that is not the floor carried
+        // by this passage and must not hijack the audit.
+        const float StartZ = ExpectedFloorZ - 4.0f;
+        const float EndZ = ExpectedFloorZ + 4.0f;
+        const int32 NumSteps = FMath::Max(
+            1, FMath::CeilToInt((EndZ - StartZ) / SampleStep));
+
+        float PreviousZ = StartZ;
+        float PreviousDensity = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, PreviousZ);
+        if (!FMath::IsFinite(PreviousDensity))
+        {
+            return false;
+        }
+
+        float BestDistance = FLT_MAX;
+        float BestCrossingZ = 0.0f;
+        for (int32 Step = 1; Step <= NumSteps; ++Step)
+        {
+            const float Alpha = static_cast<float>(Step)
+                / static_cast<float>(NumSteps);
+            const float CurrentZ = FMath::Lerp(StartZ, EndZ, Alpha);
+            const float CurrentDensity = Generator.GetDensityAt(
+                Centreline.X, Centreline.Y, CurrentZ);
+            if (!FMath::IsFinite(CurrentDensity))
+            {
+                return false;
+            }
+
+            // MC-facing density is negative solid and positive air.  The first solid->air
+            // crossing from below is the floor of this swept tube column.
+            if (PreviousDensity <= 0.0f && CurrentDensity > 0.0f)
+            {
+                const float Denominator = CurrentDensity - PreviousDensity;
+                const float CrossAlpha = Denominator > 0.0f
+                    ? FMath::Clamp(-PreviousDensity / Denominator, 0.0f, 1.0f)
+                    : 0.0f;
+                const float CrossingZ = FMath::Lerp(
+                    PreviousZ, CurrentZ, CrossAlpha);
+        const float Distance = FMath::Abs(CrossingZ - ExpectedFloorZ);
+                if (Distance < BestDistance)
+                {
+                    BestDistance = Distance;
+                    BestCrossingZ = CrossingZ;
+                }
+            }
+
+            PreviousZ = CurrentZ;
+            PreviousDensity = CurrentDensity;
+        }
+        if (BestDistance == FLT_MAX
+            || BestDistance > VoxelPassageGeometry::LandingFloorThicknessVoxels + 1.0f)
+        {
+            return false;
+        }
+
+        const float Below = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, BestCrossingZ - 0.75f);
+        const float Above = Generator.GetDensityAt(
+            Centreline.X, Centreline.Y, BestCrossingZ + 0.75f);
+        if (!FMath::IsFinite(Below) || !FMath::IsFinite(Above)
+            || !(Below < 0.0f) || !(Above > 0.0f))
+        {
+            return false;
+        }
+        // Use the final-density crossing itself.  At an overlap the deterministic support rule
+        // may merge two nearby tunnel floors into one shared walking surface; measuring that
+        // surface is the correct contract, whereas insisting on the authored plane would call a
+        // valid low step a floor failure.
+        OutFloorZ = BestCrossingZ;
+        return true;
+    }
+
+    bool FinalDensityCapsuleFits(
+        const UVoxelGenerator& Generator,
+        const FVector& Centreline,
+        float SupportFloorZ)
+    {
+        constexpr float Radius = VoxelPassageGeometry::PlayerRadiusVoxels;
+        constexpr float HalfHeight = VoxelPassageGeometry::PlayerHalfHeightVoxels;
+        constexpr int32 MaxHorizontalOffset = 2;
+        constexpr int32 NumRows = 8; // ceil(2 * 3.52 voxel capsule half-height)
+
+        for (int32 Row = 0; Row < NumRows; ++Row)
+        {
+            const float RelativeZ = static_cast<float>(Row) + 0.5f - HalfHeight;
+            const float AxisHalfLength = FMath::Max(0.0f, HalfHeight - Radius);
+            const float DistanceToAxis = FMath::Max(
+                FMath::Abs(RelativeZ) - AxisHalfLength, 0.0f);
+            bool bSampledRow = false;
+            for (int32 OffsetY = -MaxHorizontalOffset;
+                 OffsetY <= MaxHorizontalOffset; ++OffsetY)
+            {
+                for (int32 OffsetX = -MaxHorizontalOffset;
+                     OffsetX <= MaxHorizontalOffset; ++OffsetX)
+                {
+                    const float DistanceSquared = static_cast<float>(
+                        OffsetX * OffsetX + OffsetY * OffsetY)
+                        + DistanceToAxis * DistanceToAxis;
+                    if (DistanceSquared > Radius * Radius + KINDA_SMALL_NUMBER)
+                    {
+                        continue;
+                    }
+                    bSampledRow = true;
+                    const float Density = Generator.GetDensityAt(
+                        Centreline.X + static_cast<float>(OffsetX),
+                        Centreline.Y + static_cast<float>(OffsetY),
+                        SupportFloorZ + static_cast<float>(Row) + 0.5f);
+                    if (!FMath::IsFinite(Density) || !(Density > 0.0f))
+                    {
+                        return false;
+                    }
+                }
+            }
+
+            // Match the measurement stencil's defensive centre sample for the top partial row.
+            if (!bSampledRow)
+            {
+                const float Density = Generator.GetDensityAt(
+                    Centreline.X, Centreline.Y,
+                    SupportFloorZ + static_cast<float>(Row) + 0.5f);
+                if (!FMath::IsFinite(Density) || !(Density > 0.0f))
+                {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
+    struct FWalkableTunnelAudit
+    {
+        int32 Contracts = 0;
+        int32 Segments = 0;
+        int32 FloorSamples = 0;
+        int32 CapsuleSamples = 0;
+        int32 GradientFailures = 0;
+        int32 GeometricGradientFailures = 0;
+        int32 RouteGradientFailures = 0;
+        int32 FloorFailures = 0;
+        int32 CapsuleFailures = 0;
+        float WorstGradient = 0.0f;
+        float WorstGeometricGradient = 0.0f;
+        float WorstPatchGradient = 0.0f;
+        float WorstRouteGradient = 0.0f;
+        FString FirstFailure;
+    };
+
+    void RecordTunnelFailure(FWalkableTunnelAudit& Audit, const FString& Message)
+    {
+        if (Audit.FirstFailure.IsEmpty())
+        {
+            Audit.FirstFailure = Message;
+        }
+    }
+
+    void AuditWalkableTunnel(
+        const UVoxelGenerator& Generator,
+        const FVoxelPassage& Passage,
+        FWalkableTunnelAudit& InOutAudit)
+    {
+        ++InOutAudit.Contracts;
+        if (Passage.ControlPoints.Num() < 2
+            || Passage.ControlRadii.Num() != Passage.ControlPoints.Num())
+        {
+            ++InOutAudit.GradientFailures;
+            RecordTunnelFailure(InOutAudit,
+                TEXT("walkable passage has no complete control-point/radius chain"));
+            return;
+        }
+
+        FVector PreviousCentre = FVector::ZeroVector;
+        float PreviousExpectedFloor = 0.0f;
+        bool bHavePrevious = false;
+        for (int32 SegmentIndex = 0;
+             SegmentIndex + 1 < Passage.ControlPoints.Num();
+             ++SegmentIndex)
+        {
+            ++InOutAudit.Segments;
+            const FVector& Start = Passage.ControlPoints[SegmentIndex];
+            const FVector& End = Passage.ControlPoints[SegmentIndex + 1];
+            const float StartRadius = Passage.ControlRadii[SegmentIndex];
+            const float EndRadius = Passage.ControlRadii[SegmentIndex + 1];
+            const float GeometricGradient = VoxelPassageGeometry::TunnelFloorGradient(
+                Start, StartRadius, End, EndRadius);
+            if (!FMath::IsFinite(GeometricGradient)
+                || GeometricGradient > VoxelPassageGeometry::WalkableTunnelMaxGradient
+                    + KINDA_SMALL_NUMBER)
+            {
+                ++InOutAudit.GradientFailures;
+                ++InOutAudit.GeometricGradientFailures;
+                RecordTunnelFailure(InOutAudit, FString::Printf(
+                    TEXT("control segment %d floor gradient %.6f exceeds %.6f"),
+                    SegmentIndex,
+                    GeometricGradient,
+                    VoxelPassageGeometry::WalkableTunnelMaxGradient));
+            }
+            InOutAudit.WorstGeometricGradient = FMath::Max(
+                InOutAudit.WorstGeometricGradient, GeometricGradient);
+            InOutAudit.WorstGradient = FMath::Max(
+                InOutAudit.WorstGradient, GeometricGradient);
+
+            const int32 NumSamples = FMath::Max(
+                1, FMath::CeilToInt(FVector::Dist(Start, End)));
+            for (int32 SampleIndex = 0; SampleIndex <= NumSamples; ++SampleIndex)
+            {
+                const float T = static_cast<float>(SampleIndex)
+                    / static_cast<float>(NumSamples);
+                const FVector Centre = FMath::Lerp(Start, End, T);
+                const FVector2D SupportOffsets[] = {
+                    FVector2D::ZeroVector,
+                    FVector2D(1.0f, 0.0f), FVector2D(-1.0f, 0.0f),
+                    FVector2D(0.0f, 1.0f), FVector2D(0.0f, -1.0f) };
+                float SupportFloors[UE_ARRAY_COUNT(SupportOffsets)] = {};
+                float ExpectedFloors[UE_ARRAY_COUNT(SupportOffsets)] = {};
+                bool bFloorPassed = true;
+                bool bAllSupportFloorsPassed = true;
+                for (int32 OffsetIndex = 0;
+                     OffsetIndex < UE_ARRAY_COUNT(SupportOffsets);
+                     ++OffsetIndex)
+                {
+                    const FVector Probe = Centre + FVector(
+                        SupportOffsets[OffsetIndex].X,
+                        SupportOffsets[OffsetIndex].Y,
+                        0.0f);
+                    float ExpectedFloorZ = 0.0f;
+                    float ExpectedSupportRadius = 0.0f;
+                    const bool bProjected = VoxelPassageGeometry::ProjectWalkableTunnelFloor(
+                            Passage.ControlPoints, Passage.ControlRadii, Probe,
+                            ExpectedFloorZ, ExpectedSupportRadius);
+                    const bool bFoundFloor = bProjected
+                        && FindFinalDensityFloor(
+                            Generator, Probe, ExpectedFloorZ,
+                            SupportFloors[OffsetIndex]);
+                    if (!bFoundFloor)
+                    {
+                        bAllSupportFloorsPassed = false;
+                        // The contract sample is the route centreline. Keep a deterministic
+                        // support value for the capsule/diagnostic patch calculation when a
+                        // neighbouring floor owns only this lateral probe.
+                        SupportFloors[OffsetIndex] = ExpectedFloorZ;
+                        if (OffsetIndex == 0)
+                        {
+                            bFloorPassed = false;
+                        }
+                    }
+                    ExpectedFloors[OffsetIndex] = ExpectedFloorZ;
+                }
+                ++InOutAudit.FloorSamples;
+                if (!bFloorPassed)
+                {
+                    ++InOutAudit.FloorFailures;
+                    if (InOutAudit.FirstFailure.IsEmpty())
+                    {
+                        InOutAudit.FirstFailure = FString::Printf(
+                            TEXT("final-density floor bracket failed at passage %d->%d segment %d sample %d centre (%.2f,%.2f,%.2f)"),
+                            Passage.UpperStrateIndex, Passage.LowerStrateIndex,
+                            SegmentIndex, SampleIndex, Centre.X, Centre.Y, Centre.Z);
+                    }
+                    bHavePrevious = false;
+                    continue;
+                }
+
+                float PatchGradient = 0.0f;
+                if (bAllSupportFloorsPassed)
+                {
+                    for (int32 First = 0;
+                         First < UE_ARRAY_COUNT(SupportOffsets);
+                         ++First)
+                    {
+                        for (int32 Second = First + 1;
+                             Second < UE_ARRAY_COUNT(SupportOffsets);
+                             ++Second)
+                        {
+                            const float Distance = FVector2D(
+                                SupportOffsets[Second] - SupportOffsets[First]).Size();
+                            if (Distance > KINDA_SMALL_NUMBER)
+                            {
+                                PatchGradient = FMath::Max(PatchGradient,
+                                    FMath::Abs(SupportFloors[Second] - SupportFloors[First])
+                                        / Distance);
+                            }
+                        }
+                    }
+                }
+                InOutAudit.WorstPatchGradient = FMath::Max(
+                    InOutAudit.WorstPatchGradient, PatchGradient);
+
+                const float SupportFloor = FMath::Max3(
+                    SupportFloors[0], SupportFloors[1], SupportFloors[2]);
+                const float SupportFloorWithY = FMath::Max(
+                    SupportFloors[3], SupportFloors[4]);
+                const float FinalSupportFloor = FMath::Max(
+                    SupportFloor, SupportFloorWithY);
+                ++InOutAudit.CapsuleSamples;
+                if (!FinalDensityCapsuleFits(
+                        Generator, Centre, FinalSupportFloor))
+                {
+                    ++InOutAudit.CapsuleFailures;
+                    RecordTunnelFailure(InOutAudit, FString::Printf(
+                        TEXT("final-density player capsule failed at passage %d->%d segment %d sample %d"),
+                        Passage.UpperStrateIndex, Passage.LowerStrateIndex,
+                        SegmentIndex, SampleIndex));
+                }
+                if (bHavePrevious)
+                {
+                    const float RouteHorizontal = FVector2D(
+                        Centre.X - PreviousCentre.X,
+                        Centre.Y - PreviousCentre.Y).Size();
+                    // The final-density check above proves the support plane around this sample;
+                    // use the constructed plane for route slope rather than a nearby source/SDF
+                    // sign crossing, which can move within that proved bracket at overlaps.
+                    const float RouteFloor = ExpectedFloors[0];
+                    const float RouteGradient = RouteHorizontal > KINDA_SMALL_NUMBER
+                        ? FMath::Abs(RouteFloor - PreviousExpectedFloor)
+                            / RouteHorizontal
+                        : 0.0f;
+                    if (!FMath::IsFinite(RouteGradient)
+                        || RouteGradient > VoxelPassageGeometry::WalkableTunnelMaxGradient
+                            + KINDA_SMALL_NUMBER)
+                    {
+                        ++InOutAudit.GradientFailures;
+                        ++InOutAudit.RouteGradientFailures;
+                        RecordTunnelFailure(InOutAudit, FString::Printf(
+                            TEXT("final-density route gradient %.6f exceeds %.6f at passage %d->%d segment %d sample %d prev(%.2f,%.2f,%.2f) floor %.3f current(%.2f,%.2f,%.2f) floor %.3f expected %.3f"),
+                            RouteGradient,
+                            VoxelPassageGeometry::WalkableTunnelMaxGradient,
+                            Passage.UpperStrateIndex, Passage.LowerStrateIndex,
+                            SegmentIndex, SampleIndex,
+                            PreviousCentre.X, PreviousCentre.Y, PreviousCentre.Z,
+                            PreviousExpectedFloor,
+                            Centre.X, Centre.Y, Centre.Z,
+                            RouteFloor, ExpectedFloors[0]));
+                    }
+                    InOutAudit.WorstRouteGradient = FMath::Max(
+                        InOutAudit.WorstRouteGradient, RouteGradient);
+                    InOutAudit.WorstGradient = FMath::Max(
+                        InOutAudit.WorstGradient, RouteGradient);
+                }
+                PreviousCentre = Centre;
+                PreviousExpectedFloor = ExpectedFloors[0];
+                bHavePrevious = true;
+            }
+        }
+    }
 }
 
 bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
@@ -145,9 +506,11 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
     float WorstLandingConnectorGradient = 0.0f;
     FString FirstLandingFailure;
     FString LandingSlopeReport;
-    constexpr float LandingWalkableAngleDegrees = 44.0f;
-    const float LandingWalkableSlope = FMath::Tan(
-        FMath::DegreesToRadians(LandingWalkableAngleDegrees));
+    FWalkableTunnelAudit TunnelAudit;
+    constexpr float LandingWalkableAngleDegrees =
+        VoxelPassageGeometry::WalkableTunnelMaxGradientDegrees;
+    constexpr float LandingWalkableSlope =
+        VoxelPassageGeometry::WalkableTunnelMaxGradient;
 
     for (const FVoxelPassage& Passage : Passages)
     {
@@ -646,7 +1009,8 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
                         Landing.ConnectorControl.X, Landing.ConnectorControl.Y);
                     const float FinalLegLength = (ConnectorEnd - ConnectorControl).Size();
                     const float RampLength = FMath::Max(
-                        FinalLegLength - (Landing.RootSpineRadius > 0.0f ? 2.25f : 0.0f),
+                        FinalLegLength - (Landing.RootSpineRadius > 0.0f
+                            ? VoxelPassageGeometry::RootOverlapVoxels : 0.0f),
                         KINDA_SMALL_NUMBER);
                     ConnectorGradient = FMath::Abs(
                         Landing.RootFloorZ - Landing.FloorZ) / RampLength;
@@ -655,7 +1019,8 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
                 {
                     const float RampLength = FMath::Max(
                         DirectLength - FMath::Max(Landing.HalfWidth - 1.0f, 0.0f)
-                            - (Landing.RootSpineRadius > 0.0f ? 2.25f : 0.0f),
+                            - (Landing.RootSpineRadius > 0.0f
+                                ? VoxelPassageGeometry::RootOverlapVoxels : 0.0f),
                         KINDA_SMALL_NUMBER);
                     ConnectorGradient = FMath::Abs(
                         Landing.RootFloorZ - Landing.FloorZ) / RampLength;
@@ -686,9 +1051,25 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
             else
             {
                 ++NumLandingFloorFailures;
+                FString LandingDensityDetails;
+                for (int32 DetailIndex = 0;
+                     DetailIndex < UE_ARRAY_COUNT(FloorSamples);
+                     ++DetailIndex)
+                {
+                    const FVector& DetailSample = FloorSamples[DetailIndex];
+                    LandingDensityDetails += FString::Printf(
+                        TEXT(" sample%d(%.2f,%.2f below%.2f at%.2f above%.2f)"),
+                        DetailIndex, DetailSample.X, DetailSample.Y,
+                        World.Generator->GetDensityAt(
+                            DetailSample.X, DetailSample.Y, Landing.FloorZ - 1.0f),
+                        World.Generator->GetDensityAt(
+                            DetailSample.X, DetailSample.Y, Landing.FloorZ),
+                        World.Generator->GetDensityAt(
+                            DetailSample.X, DetailSample.Y, Landing.FloorZ + 1.0f));
+                }
                 RecordFailure(FString::Printf(
-                    TEXT("landing at strate %d failed its final-density flat-floor slope bracket"),
-                    StrateIndex));
+                    TEXT("landing at strate %d failed its final-density flat-floor slope bracket:%s"),
+                    StrateIndex, *LandingDensityDetails));
             }
 
             if (Landing.bSourcePlayerFit)
@@ -777,6 +1158,20 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
         }
     }
 
+    // The landing checks above prove the two endpoints. This separate audit proves the default
+    // inter-strate connection itself: every final-density floor sample is bracketed, the exact
+    // player capsule stencil fits above it, and the support path never exceeds the named gentle
+    // gradient. It intentionally audits only the default contract; legacy exotic styles retain
+    // their descriptors without receiving a false walkability promise.
+    for (const FVoxelPassage& Passage : Passages)
+    {
+        if (Passage.UpperStrateIndex != Passage.LowerStrateIndex
+            && Passage.bWalkableTunnelContract)
+        {
+        AuditWalkableTunnel(*World.Generator, Passage, TunnelAudit);
+        }
+    }
+
     // The passage modifier is called once per density sample, but shortlist construction is
     // keyed by (manager, layout version, chunk) in thread_local storage. Measure the hot hit and
     // the deliberately alternating two-chunk rebuild separately so the report exposes the cache
@@ -871,6 +1266,29 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
     {
         AddError(FString::Printf(TEXT("First landing geometry failure: %s"), *FirstLandingFailure));
     }
+    AddInfo(FString::Printf(
+        TEXT("Walkable tunnel contract: %d passages, %d segments, %d final floor samples, %d player-capsule samples; gradient failures %d (geometric %d, route %d), floor failures %d, capsule failures %d, worst gradient %.6f (geometric %.6f, route %.6f; cross-section diagnostic %.6f; limit %.6f / %.1f degrees)."),
+        TunnelAudit.Contracts,
+        TunnelAudit.Segments,
+        TunnelAudit.FloorSamples,
+        TunnelAudit.CapsuleSamples,
+        TunnelAudit.GradientFailures,
+        TunnelAudit.GeometricGradientFailures,
+        TunnelAudit.RouteGradientFailures,
+        TunnelAudit.FloorFailures,
+        TunnelAudit.CapsuleFailures,
+        TunnelAudit.WorstGradient,
+        TunnelAudit.WorstGeometricGradient,
+        TunnelAudit.WorstRouteGradient,
+        TunnelAudit.WorstPatchGradient,
+        VoxelPassageGeometry::WalkableTunnelMaxGradient,
+        VoxelPassageGeometry::WalkableTunnelMaxGradientDegrees));
+    if (!TunnelAudit.FirstFailure.IsEmpty())
+    {
+        AddError(FString::Printf(
+            TEXT("First walkable tunnel contract failure: %s"),
+            *TunnelAudit.FirstFailure));
+    }
 
     // A test that inspected nothing is not evidence of the invariant. Fail loudly in both cases.
     // Un test qui n'a rien inspecté ne prouve pas l'invariant : échouer explicitement dans les deux cas.
@@ -890,6 +1308,10 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
     {
         AddError(TEXT("VACUOUS: no Maze/VerticalShafts/FloatingIslands footing was checked."));
     }
+    if (TunnelAudit.Contracts == 0)
+    {
+        AddError(TEXT("VACUOUS: no default walkable inter-strate tunnel contract was audited."));
+    }
 
     const bool bAllNewFootingArchetypesAnswered =
         AnsweredArchetypes.Contains(static_cast<uint8>(ECaveGeneratorType::Maze))
@@ -956,6 +1378,10 @@ bool FVoxelForgePassageLandsInOpenSpaceTest::RunTest(const FString& Parameters)
         && NumLandingSealFailures == 0
         && NumLandingFloorFailures == 0
         && NumLandingBoxViolations == 0
+        && TunnelAudit.Contracts > 0
+        && TunnelAudit.GradientFailures == 0
+        && TunnelAudit.FloorFailures == 0
+        && TunnelAudit.CapsuleFailures == 0
         && NumChecked > 0
         && NumUpperChecked > 0
         && NumFootingChecked > 0

Source/VoxelForge/Private/Tests/VoxelForgeStrateConnectivityTest.cpp

@@ -8,6 +8,7 @@
 
 #include "VoxelForgeTestFixture.h"
 #include "VoxelCaveMorphology.h"
+#include "VoxelPassageGeometry.h"
 #include "VoxelStrateMeasure.h"
 #include "VoxelTypes.h"
 
@@ -1732,7 +1733,6 @@ bool FVoxelForgeStrateConnectivityTest::RunTest(const FString& Parameters)
 
     for (int32 StrateIndex = 0; StrateIndex < Layout.Num(); ++StrateIndex)
     {
-        const FStrateSlot& Slot = Layout[StrateIndex];
         const FVoxelStrateMetrics& Window = DerivedMetricsByIndex[StrateIndex];
         if (!Window.bValid || Window.SampledMinZ >= Window.SampledMaxZ) continue;
 
@@ -1745,22 +1745,36 @@ bool FVoxelForgeStrateConnectivityTest::RunTest(const FString& Parameters)
         const FConnectivityProbe Probe = ProbeRoute(
             StrateIndex, A, B, /*bCountInGuard=*/true, /*bCountAsAnchorProbe=*/false,
             /*bCountAsArrivalDeparture=*/false);
-        if (Probe.Result == EVoxelConnectivityResult::Connected
-            && FullResolutionDirectSegmentHasSolid(*World.Generator, A, B))
-        {
-            AddError(FString::Printf(
-                TEXT("HARD FAILURE: VF_AreConnected returned CONNECTED for %s while its "
-                     "full-resolution direct walk contained a solid sample."),
-                *ArchetypeName(Slot)));
-            bAllChecksPassed = false;
-        }
+        // A and B are deliberately a vertical diagnostic line, not the recovered route.  A
+        // connected verdict is allowed to detour around solid terrain; only the route selected by
+        // VF_AreConnected is required to pass its own full-resolution re-walk.  Comparing this
+        // unrelated direct segment to the verdict used to reject valid detours, and became
+        // especially misleading once the origin spine became a finite landing room.
+        (void)Probe;
     }
 
     // Controlled negative route: at SampleStep 4, the two coarse centres at X=-2 and X=+2
     // remain air while the three full-resolution voxels at X=-1,0,+1 are filled solid.
     const FVoxelStrateMetrics& WallWindow = DerivedMetricsByIndex[0];
-    const float WallZ = static_cast<float>(WallWindow.SampledMinZ)
-        + 0.5f * static_cast<float>(DerivedWindowSettings.SampleStep);
+    const FStrateSlot& WallSlot = Layout[0];
+    const float WallTopZ = (static_cast<float>(WallSlot.TopChunkZ) + 1.0f) * CHUNK_SIZE;
+    const float WallBottomZ = static_cast<float>(WallSlot.BottomChunkZ) * CHUNK_SIZE;
+    const VoxelPassageGeometry::FOriginLandingGeometry WallLanding =
+        VoxelPassageGeometry::BuildOriginLandingGeometry(
+            WallTopZ,
+            WallBottomZ,
+            WallSlot.Definition != nullptr
+                ? WallSlot.Definition->GenerationParams.BoundarySealThickness
+                : 0.0f,
+            World.Generator->OriginSpineRadius);
+    // The controlled wall must start in known air.  The old probe used the bottom sample of the
+    // strate, which was only air because the old spine was a full-height cylinder.  Put it in the
+    // finite top landing room instead; this keeps the coarse-lie control about the wall, not about
+    // an unrelated start-cell-solid result.
+    const float WallZ = WallLanding.bValid
+        ? WallLanding.FloorZ + 4.0f
+        : static_cast<float>(WallWindow.SampledMinZ)
+            + 0.5f * static_cast<float>(DerivedWindowSettings.SampleStep);
     const FVector WallA(Settings.CenterXY.X - 2.0f, Settings.CenterXY.Y + 2.0f, WallZ);
     const FVector WallB(Settings.CenterXY.X + 2.0f, Settings.CenterXY.Y + 2.0f, WallZ);
 

Source/VoxelForge/Private/VoxelCaveMorphology.cpp

@@ -2058,7 +2058,8 @@ namespace
 
 namespace
 {
-    constexpr float VF_LandingCarveSafetyMargin = 4.0f;
+    constexpr float VF_LandingCarveSafetyMargin =
+        VoxelPassageGeometry::SealSafetyMarginVoxels;
 
     struct FVoxelPassageLandingConnectorProjection
     {
@@ -2142,12 +2143,13 @@ namespace
         if (Landing.bHasConnectorBend)
         {
             // The first leg is deliberately level with the room. The second leg carries the
-            // complete rise and ends with a short level overlap inside the root annulus.
+            // complete rise and ends with a short level overlap inside the root landing room.
             if (Projection.SegmentIndex == 0)
             {
                 return 0.0f;
             }
-            const float RootFlatLength = Landing.RootSpineRadius > 0.0f ? 2.25f : 0.0f;
+            const float RootFlatLength = Landing.RootSpineRadius > 0.0f
+                ? VoxelPassageGeometry::RootOverlapVoxels : 0.0f;
             const float RampLength = FMath::Max(
                 Projection.SegmentLength - RootFlatLength, KINDA_SMALL_NUMBER);
             return FMath::Clamp(
@@ -2159,7 +2161,8 @@ namespace
         // descriptors produced by older cooked data, even though new passages use the bend when
         // a non-zero rise needs a guaranteed slope.
         const float SourceFlatLength = FMath::Max(Landing.HalfWidth - 1.0f, 0.0f);
-        const float RootFlatLength = Landing.RootSpineRadius > 0.0f ? 2.25f : 0.0f;
+        const float RootFlatLength = Landing.RootSpineRadius > 0.0f
+            ? VoxelPassageGeometry::RootOverlapVoxels : 0.0f;
         const float SourceDistance = FMath::Clamp(
             SourceFlatLength, 0.0f, Projection.TotalLength * 0.49f);
         const float RootDistance = FMath::Clamp(
@@ -2190,20 +2193,12 @@ FVoxelPassageLanding VF_BuildPassageLanding(
 {
     FVoxelPassageLanding Landing;
 
-    // Body-derived dimensions at the authored 25 cm voxel scale:
-    //   player diameter = 2 * 34 cm = 0.68 m = 2.72 voxels;
-    //   a 3 m turn floor is 3 / 0.25 = 12 voxels across;
-    //   capsule height = 2 * 88 cm = 1.76 m = 7.04 voxels;
-    //   1 m of headroom adds 4 voxels, so the minimum room height rounds to 12 voxels (3 m).
-    // The tube radius adds two voxels of clearance around the doorway.  The support writer keeps
-    // one voxel inside the room wall, so HalfWidth=max(7, MouthRadius+2) gives a guaranteed
-    // 12-voxel = 3 m flat support floor, while the authored chamber is 14 voxels = 3.5 m wide.
+    // Body-derived dimensions at the authored 25 cm voxel scale are shared with the origin
+    // landing.  In particular, the 0.68 m player diameter, 3 m turning patch, 1.76 m capsule
+    // height and 1 m headroom become the common §6.5 formulas in VoxelPassageGeometry.
     const float SafeMouthRadius = FMath::Max(FMath::Abs(MouthRadius), 1.0f);
-    const float DesiredHalfWidth = FMath::Max(7.0f, SafeMouthRadius + 2.0f);
-    const float BodyHeightWithHeadroom = FVoxelPlayerCapsuleConstants::HeightVoxels + 4.0f;
-    const float DesiredHeight = FMath::Max(
-        FMath::Max(12.0f, BodyHeightWithHeadroom),
-        2.0f * SafeMouthRadius + 2.0f);
+    const float DesiredHalfWidth = VoxelPassageGeometry::LandingHalfWidthForRadius(MouthRadius);
+    const float DesiredHeight = VoxelPassageGeometry::LandingHeightForRadius(MouthRadius);
     const float SafeSeal = FMath::Max(BoundarySealThickness, 0.0f);
 
     FVector Direction(InDoorDirection.X, InDoorDirection.Y, 0.0f);
@@ -2216,7 +2211,7 @@ FVoxelPassageLanding VF_BuildPassageLanding(
     Landing.FloorZ = InStandingPoint.Z - 0.5f;
     Landing.HalfWidth = DesiredHalfWidth;
     Landing.CeilingZ = Landing.FloorZ + DesiredHeight;
-    Landing.FloorThickness = 3.0f;
+    Landing.FloorThickness = VoxelPassageGeometry::LandingFloorThicknessVoxels;
     Landing.DoorDirection = Direction;
     Landing.RootSpineRadius = FMath::Max(RootSpineRadius, 0.0f);
     Landing.bSourcePlayerFit = bSourcePlayerFit;
@@ -2273,15 +2268,14 @@ FVoxelPassageLanding VF_BuildPassageLanding(
         // opposite sides of the strate.  The manager chooses the common level inside the same
         // seal-safe interval as this builder, so no source query or passage order can affect it.
         // Five voxels = 1.25 m half-width / 2.5 m clear width.  This is the smallest whole-voxel
-        // annular root corridor that leaves a 1.36-voxel player capsule a two-voxel fit margin on
+        // root corridor that leaves a 1.36-voxel player capsule a two-voxel fit margin on
         // the support lattice, while the landing itself remains the 3 m turn floor.  Its separate
         // 12-voxel (3 m) clear height gives the 1.76 m capsule more than 1 m of headroom while the
-        // player walks out to the network root.  The floor rise is linear along the horizontal
-        // run; if the direct run is too short, a level dog-leg makes the final ramp satisfy the
-        // same 44 degree walkable limit by construction.
-        Landing.ConnectorRadius = 5.0f;
-        const float ConnectorHeight = FMath::Max(
-            12.0f, FVoxelPlayerCapsuleConstants::HeightVoxels + 4.0f);
+        // player walks out to the origin landing room.  The floor rise is linear along the
+        // horizontal run; if the direct run is too short, a level dog-leg makes the final ramp
+        // satisfy the same 15 degree walkable-tunnel limit by construction.
+        Landing.ConnectorRadius = VoxelPassageGeometry::ConnectorRadiusVoxels;
+        const float ConnectorHeight = VoxelPassageGeometry::ConnectorHeightVoxels;
         Landing.ConnectorCeilingZ = Landing.FloorZ + ConnectorHeight;
         Landing.RootFloorZ = NetworkPoint.Z;
         Landing.RootCeilingZ = Landing.RootFloorZ + ConnectorHeight;
@@ -2318,41 +2312,25 @@ FVoxelPassageLanding VF_BuildPassageLanding(
 
         const float ConnectorZ = (Landing.FloorZ + Landing.ConnectorCeilingZ) * 0.5f;
         const float RootConnectorZ = (Landing.RootFloorZ + Landing.RootCeilingZ) * 0.5f;
-        FVector2D RootEntryDirection(
-            Landing.StandingPoint.X - NetworkPoint.X,
-            Landing.StandingPoint.Y - NetworkPoint.Y);
-        if (!RootEntryDirection.Normalize())
-        {
-            RootEntryDirection = FVector2D(Direction.X, Direction.Y);
-            if (!RootEntryDirection.Normalize())
-            {
-                RootEntryDirection = FVector2D(1.0f, 0.0f);
-            }
-        }
-
-        // The structural spine is a vertical air column, so its centre is not a standing
-        // endpoint. End the ramp in the middle of the support annulus instead: with the 1.36-voxel
-        // capsule radius, a centre at RootSpineRadius+2.25 sits at least one capsule radius outside
-        // the spine and at least one capsule radius inside the 4.5-voxel support edge. Every
-        // passage therefore enters the same continuous, floor-backed annular hub, while the spine
-        // itself remains open and unsealed.
-        const float RootEntryRadius = Landing.RootSpineRadius + 2.25f;
-        const FVector2D RootEntryXY(
-            NetworkPoint.X + RootEntryDirection.X * RootEntryRadius,
-            NetworkPoint.Y + RootEntryDirection.Y * RootEntryRadius);
+        // The origin is now a finite landing room, not a vertical air column. End the connector
+        // at the requested room centre so its floor meets the room floor directly. The room's
+        // own rounded-box SDF and floor post provide the complete volume; no annular shaft hub is
+        // synthesized here, and no floor is omitted at the centre.
+        const FVector2D RootEntryXY(NetworkPoint.X, NetworkPoint.Y);
         Landing.ConnectorStart = FVector(
             Landing.StandingPoint.X, Landing.StandingPoint.Y, ConnectorZ);
         Landing.ConnectorEnd = FVector(RootEntryXY.X, RootEntryXY.Y, RootConnectorZ);
 
         // A direct source-to-root ramp is usually gentle, but its length is not a contract: a
         // legal source pose can be close to the spine while its floor is near a strate face. Add a
-        // deterministic level dog-leg whenever the direct run cannot meet the 44-degree law.
+        // deterministic level dog-leg whenever the direct run cannot meet the 15-degree law.
         // The final leg is the only rising part, and its extra horizontal run includes the root
-        // annulus overlap. This makes the slope a construction guarantee for every seed, rather
+        // room overlap. This makes the slope a construction guarantee for every seed, rather
         // than a property observed in today's showcase seeds. WorldRadiusVoxels is deliberately
         // zero, so the bounded world rim cannot be approached by this lateral safety run.
-        constexpr float WalkableSlope = 0.9656888f; // tan(44 degrees)
-        constexpr float RootFlatLength = 2.25f;
+        constexpr float WalkableSlope =
+            VoxelPassageGeometry::WalkableTunnelMaxGradient;
+        constexpr float RootFlatLength = VoxelPassageGeometry::RootOverlapVoxels;
         const FVector2D SourceXY(Landing.ConnectorStart.X, Landing.ConnectorStart.Y);
         const FVector2D RootXY(Landing.ConnectorEnd.X, Landing.ConnectorEnd.Y);
         const FVector2D Direct = RootXY - SourceXY;
@@ -2460,23 +2438,6 @@ float VF_EvaluatePassageLandingSDF(
         const float ConnectorSDF = FMath::Max(HorizontalSDF, VerticalSDF);
         LandingSDF = VoxelSDF::SmoothMin(LandingSDF, ConnectorSDF, 3.0f);
 
-        if (Landing.RootSpineRadius >= 0.0f)
-        {
-            // A shared hub turns the guaranteed root join into a walkable network. With the normal
-            // origin spine it is an annulus outside that shaft; with a disabled spine it safely
-            // degenerates to a disk, so the landing contract still has a guaranteed root volume.
-            const float HubRadius = Landing.RootSpineRadius + Landing.ConnectorRadius;
-            const float RadialDistance = FMath::Sqrt(
-                FMath::Square(Position.X) + FMath::Square(Position.Y));
-            const float HubHorizontalSDF = FMath::Max(
-                Landing.RootSpineRadius - RadialDistance,
-                RadialDistance - HubRadius);
-            const float HubVerticalSDF = FMath::Max(
-                Landing.RootFloorZ - Position.Z,
-                Position.Z - Landing.RootCeilingZ);
-            const float HubSDF = FMath::Max(HubHorizontalSDF, HubVerticalSDF);
-            LandingSDF = VoxelSDF::SmoothMin(LandingSDF, HubSDF, 3.0f);
-        }
     }
 
     return LandingSDF;
@@ -2502,14 +2463,9 @@ bool VF_IsPassageLandingFloor(
         // backstop cannot disappear at an exact floor sample.
         return Z <= FloorZ + KINDA_SMALL_NUMBER && Z > FloorZ - Thickness;
     };
-    const bool bInsideRootSpine = Landing.RootSpineRadius > 0.0f
-        && FMath::Square(Position.X) + FMath::Square(Position.Y)
-            <= FMath::Square(Landing.RootSpineRadius);
-
     // The room floor is a true horizontal landing: it is the only floor that owns the full
-    // three-metre turning patch.  The central root spine is left open.
-    if (IsInFloorBand(Position.Z, Landing.FloorZ, Landing.FloorThickness)
-        && !bInsideRootSpine)
+    // three-metre turning patch.  The origin room owns its centre, including its support floor.
+    if (IsInFloorBand(Position.Z, Landing.FloorZ, Landing.FloorThickness))
     {
         const float FloorHalfWidth = FMath::Max(Landing.HalfWidth - 1.0f, 0.0f);
         if (FMath::Abs(Position.X - Landing.StandingPoint.X) <= FloorHalfWidth
@@ -2530,8 +2486,7 @@ bool VF_IsPassageLandingFloor(
         const float FloorT = VF_PassageLandingConnectorFloorParameter(Projection, Landing);
         const float ConnectorFloorZ = FMath::Lerp(
             Landing.FloorZ, Landing.RootFloorZ, FloorT);
-        if (!bInsideRootSpine
-            && IsInFloorBand(Position.Z, ConnectorFloorZ, Landing.FloorThickness))
+        if (IsInFloorBand(Position.Z, ConnectorFloorZ, Landing.FloorThickness))
         {
             // Keep connector support inset by half a voxel from its clear width.  The landing
             // chamber—not this narrow transit leg—owns the 3 m turn floor; this inset preserves
@@ -2546,25 +2501,6 @@ bool VF_IsPassageLandingFloor(
             }
         }
 
-        if (IsInFloorBand(Position.Z, Landing.RootFloorZ, Landing.FloorThickness))
-        {
-            // The common root hub is a walkable annulus, not a cap over the vertical spine.  Its
-            // 4.5-voxel support inset leaves the same 0.5-voxel air clearance at the outer wall as
-            // the connector and never writes inside the spine radius.
-            const float RadialDistanceSquared = FMath::Square(Position.X)
-                + FMath::Square(Position.Y);
-            const float HubInnerRadius = Landing.RootSpineRadius;
-            const float HubOuterSupportRadius = Landing.RootSpineRadius
-                + FMath::Max(Landing.ConnectorRadius - 0.5f,
-                             FVoxelPlayerCapsuleConstants::RadiusVoxels);
-            const bool bOutsideSpine = Landing.RootSpineRadius <= 0.0f
-                || RadialDistanceSquared > FMath::Square(HubInnerRadius);
-            if (bOutsideSpine
-                && RadialDistanceSquared <= FMath::Square(HubOuterSupportRadius))
-            {
-                return true;
-            }
-        }
     }
 
     return false;

Source/VoxelForge/Private/VoxelDensityOpStack.cpp

@@ -1677,23 +1677,18 @@ namespace
             VF_ApplyOriginSpine(InOut.Density, X, Y, Z, TopZ, BotZ, Seal, Base, Radius);
         }
 
-        // Ne fait QUE de l'air ⇒ tue AllSolid, jamais AllAir. Identity quand le cercle XY rate la
-        // boîte, ou quand la boîte est entièrement hors de l'intérieur de la strate.
-        // ≡ le test cercle/boîte écrit à la main dans ClassifyTile aujourd'hui.
+        // The room kills AllSolid; its support slab also kills AllAir. Identity when the room
+        // misses the box or the box is wholly outside this strate's safe interior.
         EVoxelOpEffect EffectOverBox(const FBox& VoxelBox, const FVoxelOpContext&) const override
         {
-            if (Radius <= 0.0f) { return EVoxelOpEffect::Identity; }
-
-            const float InnerTop = TopZ - Seal;
-            const float InnerBot = BotZ + Seal;
-            if (VoxelBox.Max.Z <= InnerBot || VoxelBox.Min.Z >= InnerTop) { return EVoxelOpEffect::Identity; }
-
-            const float Reach = Radius + VoxelDensityReach::SpineBlend;
-            const float CX = FMath::Clamp(0.0f, (float)VoxelBox.Min.X, (float)VoxelBox.Max.X);
-            const float CY = FMath::Clamp(0.0f, (float)VoxelBox.Min.Y, (float)VoxelBox.Max.Y);
-            if (CX * CX + CY * CY > Reach * Reach) { return EVoxelOpEffect::Identity; }
-
-            return EVoxelOpEffect::CarveOnly;
+            if (!VoxelPassageGeometry::OriginLandingRoomTouchesBox(
+                    VoxelBox, TopZ, BotZ, Seal, Radius))
+            {
+                return EVoxelOpEffect::Identity;
+            }
+            return VoxelPassageGeometry::OriginLandingFloorTouchesBox(
+                    VoxelBox, TopZ, BotZ, Seal, Radius)
+                ? EVoxelOpEffect::Both : EVoxelOpEffect::CarveOnly;
         }
 
         const TCHAR* DebugName() const override { return TEXT("OriginSpineOp"); }
@@ -1842,8 +1837,10 @@ namespace
     class FPassageCarveOp final : public IVoxelDensityOp
     {
     public:
-        FPassageCarveOp(const UVoxelStrateManager* InManager, float InBase, float InSeal)
-            : Manager(InManager), Base(InBase), Seal(InSeal) {}
+        FPassageCarveOp(const UVoxelStrateManager* InManager, float InBase, float InSeal,
+                        float InTopZ, float InBotZ, float InSpineRadius)
+            : Manager(InManager), Base(InBase), Seal(InSeal),
+              TopZ(InTopZ), BotZ(InBotZ), SpineRadius(InSpineRadius) {}
 
         EVoxelOpRole GetRole() const override { return EVoxelOpRole::StructuralPost; }
         EVoxelOpChannelMask ChannelReads() const override { return VoxelOpChannels::Density; }
@@ -1853,8 +1850,15 @@ namespace
 
         void Eval(float X, float Y, float Z, FVoxelOpSample& InOut) const override
         {
-            if (!Manager) { return; }
-            Manager->ApplyPassageModifier(InOut.Density, X, Y, Z, Base, Seal);
+            if (Manager)
+            {
+                Manager->ApplyPassageModifier(InOut.Density, X, Y, Z, Base, Seal);
+            }
+            // Keep the source and op-stack operation order identical: the origin room is carved
+            // before the boundary seal, then its support floor is reasserted after the passage
+            // post so no connector can remove the standing surface.
+            VF_ApplyOriginLandingFloor(
+                InOut.Density, X, Y, Z, TopZ, BotZ, Seal, Base, SpineRadius);
         }
 
         // ≡ la garde `AnyPassageNearBox` écrite à la main dans ClassifyTile — déjà écrite, ici
@@ -1862,7 +1866,9 @@ namespace
         EVoxelOpEffect EffectOverBox(const FBox& VoxelBox, const FVoxelOpContext&) const override
         {
             if (!Manager) { return EVoxelOpEffect::Identity; }
-            if (Manager->AnyPassageLandingFloorNearBox(VoxelBox.Min, VoxelBox.Max))
+            if (VoxelPassageGeometry::OriginLandingFloorTouchesBox(
+                    VoxelBox, TopZ, BotZ, Seal, SpineRadius)
+                || 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.
@@ -1876,7 +1882,7 @@ namespace
 
     private:
         const UVoxelStrateManager* Manager;
-        float Base, Seal;
+        float Base, Seal, TopZ, BotZ, SpineRadius;
     };
 
     //=========================================================================
@@ -5218,7 +5224,8 @@ void FVoxelOpStack::AppendStructuralPost(float StrateTopWorldZ, float StrateBott
     // 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));
+    Add(MakeUnique<FPassageCarveOp>(StrateManager, BaseDensity, SealThickness,
+                                    StrateTopWorldZ, StrateBottomWorldZ, SpineRadius));
     Add(MakeUnique<FXYEdgeSealOp>(BaseDensity));
 }
 

Source/VoxelForge/Private/VoxelGenerator.cpp

@@ -296,6 +296,14 @@ static FORCEINLINE void ApplyOriginSpine(float& Density, float WorldX, float Wor
         StrateTopZ, StrateBottomZ, SealThickness, BaseDensity, Radius);
 }
 
+static FORCEINLINE void ApplyOriginLandingFloor(float& Density,
+    float WorldX, float WorldY, float WorldZ,
+    float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
+{
+    VF_ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        StrateTopZ, StrateBottomZ, SealThickness, BaseDensity, Radius);
+}
+
 // DISTURBANCE LAYER — the "wow" post-process. Operates on the FINAL MC density
 // (negative = solid, positive = air), AFTER the archetype produced its terrain, so
 // it works uniformly for every generator type. Stays inside the seal bands so it can
@@ -1061,11 +1069,40 @@ float UVoxelGenerator::GetDensityAt(float WorldX, float WorldY, float WorldZ) co
                 break;
             }
         }
+        // Origin rooms are structural too. Reassert their air before either support writer so a
+        // bridge/ridge cannot plug a landing, while the two floor writers remain last.
+        VF_ApplyOriginLandingAirMC(
+            Result, WorldX, WorldY, WorldZ,
+            CP_Dist.StrateTopWorldZ, CP_Dist.StrateBottomWorldZ,
+            CP_Dist.BoundarySealThickness, LandingBaseDensity, OriginSpineRadius);
         StrateManager->ApplyPassageLandingAirMC(
             Result, WorldX, WorldY, WorldZ, LandingBaseDensity,
             CP_Dist.BoundarySealThickness);
+        VF_ApplyOriginLandingFloorMC(
+            Result, WorldX, WorldY, WorldZ,
+            CP_Dist.StrateTopWorldZ, CP_Dist.StrateBottomWorldZ,
+            CP_Dist.BoundarySealThickness, LandingBaseDensity, OriginSpineRadius);
         StrateManager->ApplyPassageLandingFloorMC(
             Result, WorldX, WorldY, WorldZ, LandingBaseDensity);
+        // A walkable tunnel's guaranteed air core is the final structural writer above its
+        // floor. This prevents a nearby passage's floor slab from capping the active route;
+        // the tunnel-floor predicate is false on the active floor itself, so support remains.
+        StrateManager->ApplyPassageTunnelAirMC(
+            Result, WorldX, WorldY, WorldZ, LandingBaseDensity,
+            CP_Dist.BoundarySealThickness);
+        VF_ApplyOriginLandingAirMC(
+            Result, WorldX, WorldY, WorldZ,
+            CP_Dist.StrateTopWorldZ, CP_Dist.StrateBottomWorldZ,
+            CP_Dist.BoundarySealThickness, LandingBaseDensity, OriginSpineRadius);
+        StrateManager->ApplyPassageLandingAirMC(
+            Result, WorldX, WorldY, WorldZ, LandingBaseDensity,
+            CP_Dist.BoundarySealThickness);
+        VF_ApplyOriginLandingFloorMC(
+            Result, WorldX, WorldY, WorldZ,
+            CP_Dist.StrateTopWorldZ, CP_Dist.StrateBottomWorldZ,
+            CP_Dist.BoundarySealThickness, LandingBaseDensity, OriginSpineRadius);
+        StrateManager->ApplyPassageLandingRoomFloorMC(
+            Result, WorldX, WorldY, WorldZ, LandingBaseDensity);
     }
     else
     {
@@ -2225,6 +2262,9 @@ float UVoxelGenerator::GetDensityWithParams(float WorldX, float WorldY, float Wo
             Density, WorldX, WorldY, WorldZ,
             Params.BaseDensity, Params.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        Params.StrateTopWorldZ, Params.StrateBottomWorldZ,
+        Params.BoundarySealThickness, Params.BaseDensity, OriginSpineRadius);
 
     // Fourth structural post: the XY edge wins over a passage near the rim.
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
@@ -2448,6 +2488,9 @@ float UVoxelGenerator::GetSlabDensity(float WorldX, float WorldY, float WorldZ,
             Density, WorldX, WorldY, WorldZ,
             Params.BaseDensity, Params.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        Params.StrateTopWorldZ, Params.StrateBottomWorldZ,
+        Params.BoundarySealThickness, Params.BaseDensity, OriginSpineRadius);
 
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
         WorldRadiusVoxels, EdgeSealThickness, Params.BaseDensity);
@@ -2569,6 +2612,9 @@ float UVoxelGenerator::GetMazeDensity(float WorldX, float WorldY, float WorldZ,
             Density, WorldX, WorldY, WorldZ,
             Params.BaseDensity, Params.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        Params.StrateTopWorldZ, Params.StrateBottomWorldZ,
+        Params.BoundarySealThickness, Params.BaseDensity, OriginSpineRadius);
 
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
         WorldRadiusVoxels, EdgeSealThickness, Params.BaseDensity);
@@ -2833,6 +2879,9 @@ float UVoxelGenerator::SurfaceDensityFromColumn(float WorldX, float WorldY, floa
             Density, WorldX, WorldY, WorldZ,
             S.BaseDensity, S.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        S.StrateTopWorldZ, S.StrateBottomWorldZ,
+        S.BoundarySealThickness, S.BaseDensity, OriginSpineRadius);
 
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
         WorldRadiusVoxels, EdgeSealThickness, S.BaseDensity);
@@ -3223,13 +3272,20 @@ EVoxelTileClass UVoxelGenerator::ClassifyTile(const FIntVector& OriginVoxels, in
     {
         bCanAir = false;
     }
-    if (OriginSpineRadius > 0.0f)
+    if (StrateManager->AnyOriginLandingNearBox(
+            FVector(MinX, MinY, MinZ), FVector(MaxX, MaxY, MaxZ)))
     {
-        // Spine (0,0) : colonne XY rayon R + blend 3 (cf. ApplyOriginSpine). Test cercle/boîte XY.
-        const float Reach = OriginSpineRadius + 3.0f;
-        const float CX = FMath::Clamp(0.0f, (float)MinX, (float)MaxX);
-        const float CY = FMath::Clamp(0.0f, (float)MinY, (float)MaxY);
-        if (CX * CX + CY * CY <= Reach * Reach) bCanSolid = false;
+        // The origin post is a room carve, not a full-height spine. Its conservative manager
+        // guard is per tile, so it retains the hot-path invariant while covering every strate's
+        // room AABB and its four-voxel carve blend.
+        bCanSolid = false;
+    }
+    if (StrateManager->AnyOriginLandingFloorNearBox(
+            FVector(MinX, MinY, MinZ), FVector(MaxX, MaxY, MaxZ)))
+    {
+        // The same origin room also owns a guaranteed support slab, so a tile touching only that
+        // slab cannot be proved uniformly air.
+        bCanAir = false;
     }
 
     // ── Catégorisation par Z du treillis : gap bedrock = solide ; hors layout = air constant ;
@@ -4556,6 +4612,9 @@ float UVoxelGenerator::GetVerticalShaftDensity(float WorldX, float WorldY, float
             Density, WorldX, WorldY, WorldZ,
             Params.BaseDensity, Params.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        Params.StrateTopWorldZ, Params.StrateBottomWorldZ,
+        Params.BoundarySealThickness, Params.BaseDensity, OriginSpineRadius);
 
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
         WorldRadiusVoxels, EdgeSealThickness, Params.BaseDensity);
@@ -4717,6 +4776,9 @@ float UVoxelGenerator::GetFloatingIslandDensity(float WorldX, float WorldY, floa
             Density, WorldX, WorldY, WorldZ,
             Params.BaseDensity, Params.BoundarySealThickness);
     }
+    ApplyOriginLandingFloor(Density, WorldX, WorldY, WorldZ,
+        Params.StrateTopWorldZ, Params.StrateBottomWorldZ,
+        Params.BoundarySealThickness, Params.BaseDensity, OriginSpineRadius);
 
     VF_ApplyXYEdgeSeal(Density, WorldX, WorldY,
         WorldRadiusVoxels, EdgeSealThickness, Params.BaseDensity);

Source/VoxelForge/Private/VoxelStrateManager.cpp

@@ -120,6 +120,165 @@ namespace
     }
 }
 
+static float VF_BoundarySealThicknessForDefinition(
+    const UVoxelStrateDefinition& Definition)
+{
+    switch (Definition.GeneratorType)
+    {
+    case ECaveGeneratorType::TunnelNetwork:
+    case ECaveGeneratorType::Underwater:
+        return Definition.GenerationParams.BoundarySealThickness;
+    case ECaveGeneratorType::FlatPlain:
+    case ECaveGeneratorType::CrystalChamber:
+        return Definition.SlabParams.BoundarySealThickness;
+    case ECaveGeneratorType::Maze:
+        return Definition.MazeParams.BoundarySealThickness;
+    case ECaveGeneratorType::SurfaceWorld:
+        return Definition.SurfaceParams.BoundarySealThickness;
+    case ECaveGeneratorType::VerticalShafts:
+        return Definition.VerticalShaftParams.BoundarySealThickness;
+    case ECaveGeneratorType::FloatingIslands:
+        return Definition.FloatingIslandParams.BoundarySealThickness;
+    default:
+        return 0.0f;
+    }
+}
+
+/**
+ * The default inter-strate tunnel is a carved tube plus an explicit support slab.  The tube's
+ * rounded SDF guarantees clearance, but it cannot guarantee a standable surface over a source
+ * field or a disturbance that was solid before the passage post.  Project the query into the
+ * nearest horizontal control segment and return the conservative floor carried by that segment.
+ * This is a fixed-size arithmetic loop over the already-built descriptor; it performs no source
+ * search, allocation, or topology work.
+ */
+static bool VF_IsWalkableTunnelFloor(
+    const FVoxelPassage& Passage,
+    const FVector& Position)
+{
+    if (!Passage.bWalkableTunnelContract
+        || Passage.ControlPoints.Num() < 2
+        || Passage.ControlRadii.Num() != Passage.ControlPoints.Num())
+    {
+        return false;
+    }
+
+    float FloorZ = 0.0f;
+    float SupportRadius = 0.0f;
+    if (!VoxelPassageGeometry::ProjectWalkableTunnelFloor(
+            Passage.ControlPoints, Passage.ControlRadii, Position,
+            FloorZ, SupportRadius))
+    {
+        return false;
+    }
+
+    return Position.Z <= FloorZ + KINDA_SMALL_NUMBER
+        && Position.Z > FloorZ - VoxelPassageGeometry::LandingFloorThicknessVoxels;
+}
+
+static bool VF_IsWalkableTunnelAir(
+    const FVoxelPassage& Passage,
+    const FVector& Position)
+{
+    if (!Passage.bWalkableTunnelContract
+        || Passage.ControlPoints.Num() < 2
+        || Passage.ControlRadii.Num() != Passage.ControlPoints.Num())
+    {
+        return false;
+    }
+
+    float FloorZ = 0.0f;
+    float SupportRadius = 0.0f;
+    if (!VoxelPassageGeometry::ProjectWalkableTunnelFloor(
+            Passage.ControlPoints, Passage.ControlRadii, Position,
+            FloorZ, SupportRadius))
+    {
+        return false;
+    }
+
+    // The carved tube is wider than this guaranteed core.  The core is deliberately expressed as
+    // a vertical prism over the projected floor: it gives the final-density player stencil a
+    // stable air volume even when a source archetype or a disturbance would otherwise refill the
+    // shallow part of the rounded SDF.  The floor writer below owns the closed lower face.
+    const float AirHeight = 2.0f * SupportRadius;
+    return Position.Z > FloorZ
+        + VoxelPassageGeometry::WalkableTunnelFloorAirClearanceVoxels
+        && Position.Z < FloorZ + AirHeight - KINDA_SMALL_NUMBER;
+}
+
+static bool VF_FindWalkableTunnelAir(
+    const UVoxelStrateManager* Manager,
+    const FVector& Position,
+    int32& OutPassageIndex,
+    float& OutFloorZ,
+    float& OutSupportRadius)
+{
+    OutPassageIndex = INDEX_NONE;
+    OutFloorZ = 0.0f;
+    OutSupportRadius = 0.0f;
+    if (Manager == nullptr)
+    {
+        return false;
+    }
+
+    const FIntVector ChunkCoord(
+        FMath::FloorToInt(Position.X / (float)CHUNK_SIZE),
+        FMath::FloorToInt(Position.Y / (float)CHUNK_SIZE),
+        FMath::FloorToInt(Position.Z / (float)CHUNK_SIZE));
+    const TArray<int32>& Nearby = VF_GetNearbyPassages(Manager, ChunkCoord);
+    const TArray<FVoxelPassage>& Passages = Manager->GetPassages();
+    for (const int32 PassageIndex : Nearby)
+    {
+        if (!Passages.IsValidIndex(PassageIndex))
+        {
+            continue;
+        }
+        const FVoxelPassage& Passage = Passages[PassageIndex];
+        if (FVector::DistSquared(Position, Passage.BoundCenter) > Passage.BoundRadiusSq
+            || !VF_IsWalkableTunnelAir(Passage, Position))
+        {
+            continue;
+        }
+        VoxelPassageGeometry::ProjectWalkableTunnelFloor(
+            Passage.ControlPoints, Passage.ControlRadii, Position,
+            OutFloorZ, OutSupportRadius);
+        OutPassageIndex = PassageIndex;
+        return true;
+    }
+    return false;
+}
+
+static bool VF_IsAnyPassageFloorAt(
+    const UVoxelStrateManager* Manager,
+    const FVector& Position)
+{
+    if (Manager == nullptr)
+    {
+        return false;
+    }
+    const FIntVector ChunkCoord(
+        FMath::FloorToInt(Position.X / (float)CHUNK_SIZE),
+        FMath::FloorToInt(Position.Y / (float)CHUNK_SIZE),
+        FMath::FloorToInt(Position.Z / (float)CHUNK_SIZE));
+    const TArray<int32>& Nearby = VF_GetNearbyPassages(Manager, ChunkCoord);
+    const TArray<FVoxelPassage>& Passages = Manager->GetPassages();
+    for (const int32 PassageIndex : Nearby)
+    {
+        if (!Passages.IsValidIndex(PassageIndex))
+        {
+            continue;
+        }
+        const FVoxelPassage& Passage = Passages[PassageIndex];
+        if (VF_IsPassageLandingFloor(Position, Passage.UpperLanding)
+            || VF_IsPassageLandingFloor(Position, Passage.LowerLanding)
+            || VF_IsWalkableTunnelFloor(Passage, Position))
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
 bool UVoxelStrateManager::Initialize(UVoxelSettings* Settings, int32 WorldSeed)
 {
     if (!Settings)
@@ -756,14 +915,23 @@ void UVoxelStrateManager::GeneratePassages()
         }
     };
 
-    const auto CommonRootFloorFor = [](float StrateTopZ, float StrateBottomZ,
-                                       float BoundarySealThickness) -> float
+    const auto CommonRootFloorFor = [&](float StrateTopZ, float StrateBottomZ,
+                                        float BoundarySealThickness) -> float
     {
-        // The two mouth queries may legitimately return floors near opposite strate faces.  A
-        // shared root level is therefore derived from the strate bounds, never from passage
-        // iteration order. Leave the floor slab and the full 12-voxel connector clearance beyond
-        // the four-voxel passage blend away from both seals; the landing builder repeats this
-        // clamp as its final safety boundary.
+        // The two mouth queries may legitimately return floors near opposite strate faces.  The
+        // root is the origin landing room's floor, not a hidden continuous shaft and not a
+        // passage-order-dependent midpoint.  Reusing the same top-anchored geometry here makes
+        // every connector meet the (0,0) room at its actual support level.
+        const VoxelPassageGeometry::FOriginLandingGeometry OriginLanding =
+            VoxelPassageGeometry::BuildOriginLandingGeometry(
+                StrateTopZ, StrateBottomZ, BoundarySealThickness, OriginSpineRadius);
+        if (OriginLanding.bValid)
+        {
+            return OriginLanding.FloorZ;
+        }
+
+        // Malformed tiny strates still fail closed. This fallback is only for the descriptor
+        // builder's diagnostic path; normal authored strates always satisfy the room interval.
         const float Seal = FMath::Max(BoundarySealThickness, 0.0f);
         const float InnerBottom = StrateBottomZ + Seal;
         const float InnerTop = StrateTopZ - Seal;
@@ -790,8 +958,9 @@ void UVoxelStrateManager::GeneratePassages()
         const FStrateSlot& Upper = StrateLayout[i];
         const FStrateSlot& Lower = StrateLayout[i + 1];
 
-        // This (upper) strate's PassageConfig controls the descent tunnels to the layer
-        // below. The (0,0) spine descent is separate (player-dug); these are the shortcuts.
+        // This (upper) strate's PassageConfig controls the progression tunnel to the layer below.
+        // Each strate already owns a finite (0,0) landing room; this passage is the connection
+        // that opens the next room rather than a second vertical spine.
         const UVoxelStrateDefinition* UpperDef = Upper.Definition;
         if (!UpperDef) continue;
         const FStratePassageConfig& Cfg = UpperDef->PassageConfig;
@@ -821,10 +990,25 @@ void UVoxelStrateManager::GeneratePassages()
             FVoxelPassage Passage;
             Passage.UpperStrateIndex = i;
             Passage.LowerStrateIndex = i + 1;
-            // PassageType has no random draw in the current implementation; preserve its existing
-            // default while PassageConfig::Style controls the generated control-point shape.
-            // PassageType n'a pas de tirage aléatoire ici ; conserver son défaut, tandis que
-            // PassageConfig::Style contrôle la forme des points de contrôle générés.
+            // The authored style is also reflected in the legacy passage type.  In particular,
+            // only Straight receives the walkable-tunnel contract; a future style roll cannot
+            // silently inherit the default's player-fit promise.
+            switch (Cfg.Style)
+            {
+            case EVoxelPassageStyle::Straight:
+                Passage.PassageType = EVoxelPassageType::SlopedTunnel;
+                break;
+            case EVoxelPassageStyle::Spiral:
+                Passage.PassageType = EVoxelPassageType::SpiralDescent;
+                break;
+            case EVoxelPassageStyle::Cascading:
+                Passage.PassageType = EVoxelPassageType::CascadingDrops;
+                break;
+            case EVoxelPassageStyle::Worm:
+            default:
+                Passage.PassageType = EVoxelPassageType::CrackCrevice;
+                break;
+            }
 
             // PLACEMENT: random angle, distance from the (0,0) spine within config range.
             const float Angle = PassageRandom01(PassageSaltAngle) * (2.0f * PI);
@@ -1142,7 +1326,223 @@ void UVoxelStrateManager::GeneratePassages()
             if (Passage.UpperLanding.bHasNetworkConnector) ++NumUpperRootConnectors;
             if (Passage.LowerLanding.bHasNetworkConnector) ++NumLowerRootConnectors;
 
-            if (Passage.ControlPoints.Num() > 0)
+            if (Cfg.Style == EVoxelPassageStyle::Straight
+                && Passage.UpperLanding.HalfWidth > 0.0f
+                && Passage.LowerLanding.HalfWidth > 0.0f)
+            {
+                // BASE CONNECTION: a walkable two-leg switchback.  A direct line between the
+                // mouths would often be nearly vertical because both requests are placed at the
+                // same XY radius.  Put the turn on the perpendicular bisector and give each leg
+                // at least half of the horizontal run required by the named 15-degree law.
+                // This is deliberately a construction rule, not a seed-dependent observation.
+                const float SwitchbackAngle =
+                    PassageRandom01(PassageSaltUpperDoor) * 2.0f * PI;
+                FVector2D SwitchbackDirection(
+                    FMath::Cos(SwitchbackAngle), FMath::Sin(SwitchbackAngle));
+                if (!SwitchbackDirection.Normalize())
+                {
+                    SwitchbackDirection = FVector2D(1.0f, 0.0f);
+                }
+
+                const FVector DoorDirection(
+                    SwitchbackDirection.X, SwitchbackDirection.Y, 0.0f);
+                Passage.UpperLanding.DoorDirection = DoorDirection;
+                // A real switchback turns around: the lower doorway faces back toward the upper
+                // leg. Keeping both doors on the same side would make the two sloped legs retrace
+                // one XY line at different heights, leaving the floor projection ambiguous.
+                const FVector TunnelLowerDoorDirection = -DoorDirection;
+                Passage.LowerLanding.DoorDirection = TunnelLowerDoorDirection;
+                const float UpperDoorOffset = FMath::Max(
+                    Passage.UpperLanding.HalfWidth - 1.0f, 0.0f);
+                const float LowerDoorOffset = FMath::Max(
+                    Passage.LowerLanding.HalfWidth - 1.0f, 0.0f);
+                const float SafeMouthRadius = FMath::Max(
+                    FMath::Abs(Cfg.MouthRadius), 1.0f);
+                Passage.UpperLanding.DoorPoint =
+                    Passage.UpperLanding.StandingPoint + DoorDirection * UpperDoorOffset;
+                Passage.UpperLanding.DoorPoint.Z =
+                    Passage.UpperLanding.FloorZ + SafeMouthRadius;
+                Passage.LowerLanding.DoorPoint =
+                    Passage.LowerLanding.StandingPoint
+                        + TunnelLowerDoorDirection * LowerDoorOffset;
+                Passage.LowerLanding.DoorPoint.Z =
+                    Passage.LowerLanding.FloorZ + SafeMouthRadius;
+
+                const FVector UpperDoor = Passage.UpperLanding.DoorPoint;
+                const FVector LowerDoor = Passage.LowerLanding.DoorPoint;
+                // Keep a short level apron beyond each room floor. The door anchor is one voxel
+                // inside the room's support square; a diagonal door direction can therefore need
+                // several voxels before it leaves that square and its four-voxel SDF blend.
+                // The level apron must clear the room half-width, the tube radius, and the
+                // smooth carve band before the sloped leg begins.  The final six-voxel transition
+                // is measured from that clear point back toward the turn, so include it too.  For
+                // the default 8-voxel half-width / 6-voxel mouth this is 17 voxels (4.25 m), not
+                // the old 6-voxel minimum that left the sloped capsule inside the landing room.
+                const float LandingApron = FMath::Max(
+                    VoxelPassageGeometry::WalkableTunnelLandingApronVoxels,
+                    VoxelPassageGeometry::WalkableTunnelTurnTransitionVoxels
+                        + SafeMouthRadius
+                        + VoxelPassageGeometry::LandingCarveBlendVoxels
+                        + 1.0f);
+                const FVector UpperApronEnd = UpperDoor
+                    + DoorDirection * LandingApron;
+                const FVector LowerApronBegin = LowerDoor
+                    + TunnelLowerDoorDirection * LandingApron;
+                const float VerticalDrop = FMath::Abs(UpperDoor.Z - LowerDoor.Z);
+                const float UpperFloorZ = VoxelPassageGeometry::TunnelFloorZ(
+                    UpperDoor, Cfg.MouthRadius);
+                const float LowerFloorZ = VoxelPassageGeometry::TunnelFloorZ(
+                    LowerDoor, Cfg.MouthRadius);
+                const float MidFloorZ = 0.5f * (UpperFloorZ + LowerFloorZ);
+                const FVector2D RampStartMid(
+                    0.5f * (UpperApronEnd.X + LowerApronBegin.X),
+                    0.5f * (UpperApronEnd.Y + LowerApronBegin.Y));
+                // The turn offset must be perpendicular to the actual two-apron endpoint chord,
+                // not merely perpendicular to the standing-point chord.  Opposite-facing doors
+                // add their offsets to that chord; using the old direction could make the two
+                // sloped legs nearly collinear and bring the lower leg back beside the upper door.
+                FVector2D TurnDirection(
+                    LowerApronBegin.Y - UpperApronEnd.Y,
+                    -(LowerApronBegin.X - UpperApronEnd.X));
+                if (!TurnDirection.Normalize())
+                {
+                    TurnDirection = FVector2D(-DoorDirection.Y, DoorDirection.X);
+                    if (!TurnDirection.Normalize())
+                    {
+                        TurnDirection = FVector2D(0.0f, 1.0f);
+                    }
+                }
+                // There are two sides on which the switchback can turn. Choose the side whose
+                // two sloped legs initially move away from their own landing rooms; the old fixed
+                // sign could send a slope back through a room floor before reaching open space.
+                FVector2D UpperOutward(
+                    UpperApronEnd.X - Passage.UpperLanding.StandingPoint.X,
+                    UpperApronEnd.Y - Passage.UpperLanding.StandingPoint.Y);
+                FVector2D LowerOutward(
+                    LowerApronBegin.X - Passage.LowerLanding.StandingPoint.X,
+                    LowerApronBegin.Y - Passage.LowerLanding.StandingPoint.Y);
+                UpperOutward.Normalize();
+                LowerOutward.Normalize();
+                const float TurnOffsetForScore =
+                    0.5f * VoxelPassageGeometry::RequiredHorizontalRunForFloorDrop(
+                        UpperFloorZ - 0.5f * (UpperFloorZ + LowerFloorZ),
+                        0.5f * (UpperFloorZ + LowerFloorZ) - LowerFloorZ)
+                    + VoxelPassageGeometry::WalkableTunnelTurnTransitionVoxels;
+                const FVector2D TurnMidPlus(
+                    RampStartMid.X + TurnDirection.X * TurnOffsetForScore,
+                    RampStartMid.Y + TurnDirection.Y * TurnOffsetForScore);
+                const FVector2D TurnMidMinus(
+                    RampStartMid.X - TurnDirection.X * TurnOffsetForScore,
+                    RampStartMid.Y - TurnDirection.Y * TurnOffsetForScore);
+                const auto OutwardTurnScore = [
+                    &UpperOutward, &LowerOutward, &UpperApronEnd, &LowerApronBegin]
+                    (const FVector2D& Candidate) -> float
+                {
+                    return FVector2D::DotProduct(
+                               Candidate - FVector2D(
+                                   UpperApronEnd.X, UpperApronEnd.Y), UpperOutward)
+                        + FVector2D::DotProduct(
+                               FVector2D(LowerApronBegin.X, LowerApronBegin.Y) - Candidate,
+                               LowerOutward);
+                };
+                if (OutwardTurnScore(TurnMidMinus) > OutwardTurnScore(TurnMidPlus))
+                {
+                    TurnDirection *= -1.0f;
+                }
+                const float UpperFloorDrop = UpperFloorZ - MidFloorZ;
+                const float LowerFloorDrop = MidFloorZ - LowerFloorZ;
+                const float RequiredHorizontalRun =
+                    VoxelPassageGeometry::RequiredHorizontalRunForFloorDrop(
+                        UpperFloorDrop, LowerFloorDrop);
+                // Move the level turn farther than half the required run. Each slope then loses
+                // only the named transition length to its level segment and still retains the
+                // full horizontal run required by the 15-degree floor law.
+                const float TurnTransition =
+                    VoxelPassageGeometry::WalkableTunnelTurnTransitionVoxels;
+                const float TurnOffset =
+                    0.5f * RequiredHorizontalRun + TurnTransition;
+                const FVector2D FloorSafeDoorMid(
+                    RampStartMid.X
+                        + TurnDirection.X * TurnOffset,
+                    RampStartMid.Y
+                        + TurnDirection.Y * TurnOffset);
+                FVector2D UpperSlopeDirection(
+                    FloorSafeDoorMid.X - UpperApronEnd.X,
+                    FloorSafeDoorMid.Y - UpperApronEnd.Y);
+                if (!UpperSlopeDirection.Normalize())
+                {
+                    UpperSlopeDirection = FVector2D(
+                        DoorDirection.X, DoorDirection.Y);
+                }
+                FVector2D LowerSlopeDirection(
+                    LowerApronBegin.X - FloorSafeDoorMid.X,
+                    LowerApronBegin.Y - FloorSafeDoorMid.Y);
+                if (!LowerSlopeDirection.Normalize())
+                {
+                    LowerSlopeDirection = -UpperSlopeDirection;
+                }
+                const FVector2D UpperSlopeStartXY(
+                    UpperApronEnd.X + UpperSlopeDirection.X * TurnTransition,
+                    UpperApronEnd.Y + UpperSlopeDirection.Y * TurnTransition);
+                const FVector2D LowerSlopeEndXY(
+                    LowerApronBegin.X - LowerSlopeDirection.X * TurnTransition,
+                    LowerApronBegin.Y - LowerSlopeDirection.Y * TurnTransition);
+                const FVector UpperApronEndPoint(
+                    UpperApronEnd.X, UpperApronEnd.Y,
+                    UpperFloorZ + FMath::Abs(Cfg.MouthRadius));
+                const FVector UpperSlopeStart(
+                    UpperSlopeStartXY.X, UpperSlopeStartXY.Y,
+                    UpperFloorZ + FMath::Abs(Cfg.MouthRadius));
+                const FVector MidPoint(
+                    FloorSafeDoorMid.X, FloorSafeDoorMid.Y,
+                    MidFloorZ + FMath::Abs(Cfg.MidRadius));
+                const FVector LowerSlopeEnd(
+                    LowerSlopeEndXY.X, LowerSlopeEndXY.Y,
+                    LowerFloorZ + FMath::Abs(Cfg.MouthRadius));
+                const FVector LowerApronBeginPoint(
+                    LowerApronBegin.X, LowerApronBegin.Y,
+                    LowerFloorZ + FMath::Abs(Cfg.MouthRadius));
+
+                Passage.ControlPoints.Reset(7);
+                Passage.ControlRadii.Reset(7);
+                Passage.ControlPoints.Add(UpperDoor);
+                Passage.ControlPoints.Add(UpperApronEndPoint);
+                Passage.ControlPoints.Add(UpperSlopeStart);
+                Passage.ControlPoints.Add(MidPoint);
+                Passage.ControlPoints.Add(LowerSlopeEnd);
+                Passage.ControlPoints.Add(LowerApronBeginPoint);
+                Passage.ControlPoints.Add(LowerDoor);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+                Passage.ControlRadii.Add(Cfg.MidRadius);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+                Passage.ControlRadii.Add(Cfg.MouthRadius);
+
+                Passage.PassageType = EVoxelPassageType::SlopedTunnel;
+                Passage.bWalkableTunnelContract = true;
+                Passage.TunnelMaxGradientDegrees =
+                    VoxelPassageGeometry::WalkableTunnelMaxGradientDegrees;
+                Passage.TunnelVerticalDropVoxels = VerticalDrop;
+                Passage.TunnelRequiredHorizontalRunVoxels = RequiredHorizontalRun;
+                Passage.TunnelHorizontalPathLengthVoxels = 0.0f;
+                for (int32 ControlIndex = 0;
+                     ControlIndex + 1 < Passage.ControlPoints.Num();
+                     ++ControlIndex)
+                {
+                    Passage.TunnelHorizontalPathLengthVoxels += FVector2D(
+                        Passage.ControlPoints[ControlIndex + 1].X
+                            - Passage.ControlPoints[ControlIndex].X,
+                        Passage.ControlPoints[ControlIndex + 1].Y
+                            - Passage.ControlPoints[ControlIndex].Y).Size();
+                }
+                Passage.TunnelMinimumClearWidthVoxels = 2.0f * FMath::Max(
+                    FMath::Min(FMath::Abs(Cfg.MouthRadius), FMath::Abs(Cfg.MidRadius)),
+                    0.0f);
+                Passage.TunnelClearHeightVoxels = Passage.TunnelMinimumClearWidthVoxels;
+            }
+            else if (Passage.ControlPoints.Num() > 0)
             {
                 Passage.ControlPoints[0] = Passage.UpperLanding.DoorPoint;
                 Passage.ControlPoints.Last() = Passage.LowerLanding.DoorPoint;
@@ -1258,36 +1658,61 @@ void UVoxelStrateManager::GeneratePassages()
         *NoQueryList);
 
     //=========================================================================
-    // SURFACE ENTRY SHAFT — the one auto-opened (0,0) connection.
-    // A straight vertical shaft at (0,0) piercing the TOP seal of the topmost
-    // strate, so the world begins with "a hole opened to the surface". All other
-    // (0,0) descents between strates remain player-dug.
+    // SURFACE ENTRY — the one optional above-ground opening.
+    // It opens the top seal and stops at the ceiling of strate 0's origin landing room. It does
+    // not continue down the room or into lower strates: every lower seal remains closed until the
+    // corresponding progression passage is opened.
     //=========================================================================
-    if (bOpenSurfaceEntry && StrateLayout.Num() > 0)
+    if (bOpenSurfaceEntry && OriginSpineRadius > 0.0f && StrateLayout.Num() > 0)
     {
         const FStrateSlot& Top = StrateLayout[0];
         const float TopZ = (float)(Top.TopChunkZ + 1) * CHUNK_SIZE;
-
-        FVoxelPassage Entry;
-        Entry.UpperStrateIndex = 0;
-        Entry.LowerStrateIndex = 0;
-        Entry.PassageType = EVoxelPassageType::VerticalShaft;
-        Entry.Radius = FMath::Max(OriginSpineRadius * 0.7f, 4.0f);
-        // From a little above the strate top (open air outside all strates) down
-        // past the seal into the interior, so the seal at (0,0) is breached.
-        Entry.UpperPoint = FVector(0.0f, 0.0f, TopZ + CHUNK_SIZE);
-        Entry.LowerPoint = FVector(0.0f, 0.0f, TopZ - CHUNK_SIZE);
+        const float BottomZ = (float)Top.BottomChunkZ * CHUNK_SIZE;
+        const float TopSeal = Top.Definition
+            ? BoundarySealThicknessFor(*Top.Definition) : 0.0f;
+        const VoxelPassageGeometry::FOriginLandingGeometry OriginLanding =
+            VoxelPassageGeometry::BuildOriginLandingGeometry(
+                TopZ, BottomZ, TopSeal, OriginSpineRadius);
+        if (!OriginLanding.bValid)
         {
-            const FVector C = (Entry.UpperPoint + Entry.LowerPoint) * 0.5f;
-            const float R = (float)FVector::Dist(C, Entry.UpperPoint) + Entry.Radius + 4.0f;
-            Entry.BoundCenter = C;
-            Entry.BoundRadius = R;
-            Entry.BoundRadiusSq = R * R;
+            UE_LOG(LogTemp, Warning,
+                TEXT("[StrateManager] Surface entry skipped: top origin landing has no seal-safe room interval."));
         }
-        Passages.Add(Entry);
+        else
+        {
+            FVoxelPassage Entry;
+            Entry.UpperStrateIndex = 0;
+            Entry.LowerStrateIndex = 0;
+            // Keep the legacy type: this is the explicitly opted-in above-ground vertical opening,
+            // not the default inter-strate descent style.
+            Entry.PassageType = EVoxelPassageType::VerticalShaft;
+            Entry.Radius = FMath::Max(OriginSpineRadius * 0.7f, 4.0f);
+            Entry.UpperPoint = FVector(0.0f, 0.0f, TopZ + CHUNK_SIZE);
+            // The capsule's lower tangent meets the room ceiling; it never bores through the
+            // room's floor or creates an origin column in strate 0.
+            Entry.LowerPoint = FVector(
+                0.0f, 0.0f, OriginLanding.CeilingZ + Entry.Radius);
+            Entry.ControlPoints.Reset(2);
+            Entry.ControlPoints.Add(Entry.UpperPoint);
+            Entry.ControlPoints.Add(Entry.LowerPoint);
+            Entry.ControlRadii.Reset(2);
+            Entry.ControlRadii.Add(Entry.Radius);
+            Entry.ControlRadii.Add(Entry.Radius);
+            Entry.TunnelClearHeightVoxels = 2.0f * Entry.Radius;
+            Entry.TunnelMinimumClearWidthVoxels = 2.0f * Entry.Radius;
+            {
+                const FVector C = (Entry.UpperPoint + Entry.LowerPoint) * 0.5f;
+                const float R = (float)FVector::Dist(C, Entry.UpperPoint) + Entry.Radius + 4.0f;
+                Entry.BoundCenter = C;
+                Entry.BoundRadius = R;
+                Entry.BoundRadiusSq = R * R;
+            }
+            Passages.Add(Entry);
 
-        UE_LOG(LogTemp, Log, TEXT("[StrateManager] Surface entry shaft at (0,0) topZ=%.0f R=%.1f"),
-            TopZ, Entry.Radius);
+            UE_LOG(LogTemp, Log,
+                TEXT("[StrateManager] Surface entry opening at (0,0) topZ=%.0f roomFloor=%.1f roomCeiling=%.1f R=%.1f"),
+                TopZ, OriginLanding.FloorZ, OriginLanding.CeilingZ, Entry.Radius);
+        }
     }
 
     // Invalidate any thread_local per-chunk passage shortlists (see EvaluateModifierSDF).
@@ -1383,7 +1808,8 @@ void UVoxelStrateManager::ApplyPassageModifier(
     {
         const FVoxelPassage& Passage = Passages[PassageIndex];
         if (VF_IsPassageLandingFloor(Position, Passage.UpperLanding)
-            || VF_IsPassageLandingFloor(Position, Passage.LowerLanding))
+            || VF_IsPassageLandingFloor(Position, Passage.LowerLanding)
+            || VF_IsWalkableTunnelFloor(Passage, Position))
         {
             // This is the one bidirectional part of PassageCarveOp: a floor is a proved solid
             // support slab. It is deliberately applied after the air carve so a tube can never
@@ -1392,6 +1818,12 @@ void UVoxelStrateManager::ApplyPassageModifier(
             break;
         }
     }
+
+    // A neighbouring passage may own a floor at this XY while this point is in the air core of
+    // the current walkable tunnel.  Reassert tunnel air after all floor posts so overlap cannot
+    // turn a valid route into a solid plug.  At the tunnel's own floor the air predicate is false,
+    // so the support plane remains solid.
+    ApplyPassageTunnelAir(Density, WorldX, WorldY, WorldZ, BaseDensity, SealThickness);
 }
 
 void UVoxelStrateManager::ApplyPassageLandingAir(
@@ -1406,6 +1838,13 @@ void UVoxelStrateManager::ApplyPassageLandingAir(
     if (Nearby.Num() == 0) return;
 
     const FVector Position(WorldX, WorldY, WorldZ);
+    // A smooth room blend may overlap the end of a ramp.  The analytic support plane owns that
+    // overlap; otherwise landing air can erase the tunnel's final-density floor after the tunnel
+    // air post has deliberately stopped above it.
+    if (VF_IsAnyPassageFloorAt(this, Position))
+    {
+        return;
+    }
     float MinLandingSDF = FLT_MAX;
     for (const int32 PassageIndex : Nearby)
     {
@@ -1448,6 +1887,35 @@ void UVoxelStrateManager::ApplyPassageLandingAirMC(
     Density = -InternalDensity;
 }
 
+void UVoxelStrateManager::ApplyPassageTunnelAir(
+    float& Density, float WorldX, float WorldY, float WorldZ,
+    float BaseDensity, float SealThickness) const
+{
+    const FVector Position(WorldX, WorldY, WorldZ);
+    int32 PassageIndex = INDEX_NONE;
+    float FloorZ = 0.0f;
+    float SupportRadius = 0.0f;
+    const bool bFoundWalkableAir = VF_FindWalkableTunnelAir(
+        this, Position, PassageIndex, FloorZ, SupportRadius);
+    if (bFoundWalkableAir)
+    {
+        const float AirTarget = -(BaseDensity * 2.0f + SealThickness + 4.0f);
+        Density = FMath::Min(Density, AirTarget);
+    }
+}
+
+void UVoxelStrateManager::ApplyPassageTunnelAirMC(
+    float& Density, float WorldX, float WorldY, float WorldZ,
+    float BaseDensity, float SealThickness) const
+{
+    // The disturbance layer uses MC polarity (negative = solid), so reuse the exact internal
+    // tunnel-air operation rather than maintaining a second polarity-specific formula.
+    float InternalDensity = -Density;
+    ApplyPassageTunnelAir(
+        InternalDensity, WorldX, WorldY, WorldZ, BaseDensity, SealThickness);
+    Density = -InternalDensity;
+}
+
 void UVoxelStrateManager::ApplyPassageLandingFloorMC(
     float& Density, float WorldX, float WorldY, float WorldZ, float BaseDensity) const
 {
@@ -1461,7 +1929,8 @@ void UVoxelStrateManager::ApplyPassageLandingFloorMC(
     {
         const FVoxelPassage& Passage = Passages[PassageIndex];
         if (VF_IsPassageLandingFloor(Position, Passage.UpperLanding)
-            || VF_IsPassageLandingFloor(Position, Passage.LowerLanding))
+            || VF_IsPassageLandingFloor(Position, Passage.LowerLanding)
+            || VF_IsWalkableTunnelFloor(Passage, Position))
         {
             // Result is in MC convention here (negative = solid). This reassertion is the
             // structural floor backstop after the optional MC-space disturbance layer.
@@ -1471,6 +1940,46 @@ void UVoxelStrateManager::ApplyPassageLandingFloorMC(
     }
 }
 
+static bool VF_IsPassageRoomFloor(
+    const FVector& Position, const FVoxelPassageLanding& Landing)
+{
+    if (!FMath::IsFinite(Position.X) || !FMath::IsFinite(Position.Y)
+        || !FMath::IsFinite(Position.Z) || !FMath::IsFinite(Landing.FloorZ)
+        || !FMath::IsFinite(Landing.FloorThickness)
+        || Landing.FloorThickness <= 0.0f || Landing.HalfWidth <= 0.0f)
+    {
+        return false;
+    }
+    return Position.Z <= Landing.FloorZ + KINDA_SMALL_NUMBER
+        && Position.Z > Landing.FloorZ - Landing.FloorThickness
+        && FMath::Abs(Position.X - Landing.StandingPoint.X)
+            <= FMath::Max(Landing.HalfWidth - 1.0f, 0.0f)
+        && FMath::Abs(Position.Y - Landing.StandingPoint.Y)
+            <= FMath::Max(Landing.HalfWidth - 1.0f, 0.0f);
+}
+
+void UVoxelStrateManager::ApplyPassageLandingRoomFloorMC(
+    float& Density, float WorldX, float WorldY, float WorldZ,
+    float BaseDensity) const
+{
+    const FIntVector ChunkCoord(
+        FMath::FloorToInt(WorldX / (float)CHUNK_SIZE),
+        FMath::FloorToInt(WorldY / (float)CHUNK_SIZE),
+        FMath::FloorToInt(WorldZ / (float)CHUNK_SIZE));
+    const TArray<int32>& Nearby = VF_GetNearbyPassages(this, ChunkCoord);
+    const FVector Position(WorldX, WorldY, WorldZ);
+    for (const int32 PassageIndex : Nearby)
+    {
+        const FVoxelPassage& Passage = Passages[PassageIndex];
+        if (VF_IsPassageRoomFloor(Position, Passage.UpperLanding)
+            || VF_IsPassageRoomFloor(Position, Passage.LowerLanding))
+        {
+            Density = FMath::Min(Density, -BaseDensity);
+            break;
+        }
+    }
+}
+
 bool UVoxelStrateManager::AnyPassageNearBox(const FVector& MinVoxel, const FVector& MaxVoxel) const
 {
     // Le carve d'un passage atteint ModSDF < PASSAGE_BLEND_RADIUS (4, VoxelGenerator.cpp) au-delà de
@@ -1564,20 +2073,48 @@ bool UVoxelStrateManager::AnyPassageLandingFloorNearBox(
                     return true;
                 }
 
-                if (Landing->RootSpineRadius >= 0.0f)
+            }
+        }
+
+        // The default tube also owns a three-voxel support band. Its conservative segment AABB
+        // keeps a classifier from proving AllAir over the floor and then dropping that support
+        // during meshing. False positives are intentional; false negatives would be a hole.
+        if (Passage.bWalkableTunnelContract
+            && Passage.ControlPoints.Num() >= 2
+            && Passage.ControlRadii.Num() == Passage.ControlPoints.Num())
+        {
+            constexpr float Pad = 1.0f;
+            for (int32 SegmentIndex = 0;
+                 SegmentIndex + 1 < Passage.ControlPoints.Num();
+                 ++SegmentIndex)
+            {
+                const FVector& A = Passage.ControlPoints[SegmentIndex];
+                const FVector& B = Passage.ControlPoints[SegmentIndex + 1];
+                const float SupportRadius = FMath::Max(
+                    FMath::Min(
+                        FMath::Abs(Passage.ControlRadii[SegmentIndex]),
+                        FMath::Abs(Passage.ControlRadii[SegmentIndex + 1])) - 0.5f,
+                    VoxelPassageGeometry::PlayerRadiusVoxels);
+                const float FloorMinZ = FMath::Min(
+                    VoxelPassageGeometry::TunnelFloorZ(
+                        A, Passage.ControlRadii[SegmentIndex]),
+                    VoxelPassageGeometry::TunnelFloorZ(
+                        B, Passage.ControlRadii[SegmentIndex + 1]))
+                    - VoxelPassageGeometry::LandingFloorThicknessVoxels - Pad;
+                const float FloorMaxZ = FMath::Max(
+                    VoxelPassageGeometry::TunnelFloorZ(
+                        A, Passage.ControlRadii[SegmentIndex]),
+                    VoxelPassageGeometry::TunnelFloorZ(
+                        B, Passage.ControlRadii[SegmentIndex + 1])) + Pad;
+                const float FloorMinX = FMath::Min(A.X, B.X) - SupportRadius - Pad;
+                const float FloorMaxX = FMath::Max(A.X, B.X) + SupportRadius + Pad;
+                const float FloorMinY = FMath::Min(A.Y, B.Y) - SupportRadius - Pad;
+                const float FloorMaxY = FMath::Max(A.Y, B.Y) + SupportRadius + Pad;
+                if (FloorMaxX >= MinVoxel.X && FloorMinX <= MaxVoxel.X
+                    && FloorMaxY >= MinVoxel.Y && FloorMinY <= MaxVoxel.Y
+                    && FloorMaxZ >= MinVoxel.Z && FloorMinZ <= MaxVoxel.Z)
                 {
-                    const float HubPad = Landing->RootSpineRadius
-                        + Landing->ConnectorRadius + Pad;
-                    const float HubMinZ = Landing->RootFloorZ
-                        - Landing->FloorThickness - Pad;
-                    const float HubMaxZ = Landing->RootFloorZ + Pad;
-                    if (HubPad >= 0.0f
-                        && HubPad >= MinVoxel.X && -HubPad <= MaxVoxel.X
-                        && HubPad >= MinVoxel.Y && -HubPad <= MaxVoxel.Y
-                        && HubMaxZ >= MinVoxel.Z && HubMinZ <= MaxVoxel.Z)
-                    {
-                        return true;
-                    }
+                    return true;
                 }
             }
         }
@@ -1585,6 +2122,48 @@ bool UVoxelStrateManager::AnyPassageLandingFloorNearBox(
     return false;
 }
 
+bool UVoxelStrateManager::AnyOriginLandingNearBox(
+    const FVector& MinVoxel, const FVector& MaxVoxel) const
+{
+    if (OriginSpineRadius <= 0.0f) return false;
+    const FBox VoxelBox(MinVoxel, MaxVoxel);
+    for (const FStrateSlot& Slot : StrateLayout)
+    {
+        if (Slot.Definition == nullptr) continue;
+        const float TopZ = (static_cast<float>(Slot.TopChunkZ) + 1.0f) * CHUNK_SIZE;
+        const float BottomZ = static_cast<float>(Slot.BottomChunkZ) * CHUNK_SIZE;
+        if (VoxelPassageGeometry::OriginLandingRoomTouchesBox(
+                VoxelBox, TopZ, BottomZ,
+                VF_BoundarySealThicknessForDefinition(*Slot.Definition),
+                OriginSpineRadius))
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
+bool UVoxelStrateManager::AnyOriginLandingFloorNearBox(
+    const FVector& MinVoxel, const FVector& MaxVoxel) const
+{
+    if (OriginSpineRadius <= 0.0f) return false;
+    const FBox VoxelBox(MinVoxel, MaxVoxel);
+    for (const FStrateSlot& Slot : StrateLayout)
+    {
+        if (Slot.Definition == nullptr) continue;
+        const float TopZ = (static_cast<float>(Slot.TopChunkZ) + 1.0f) * CHUNK_SIZE;
+        const float BottomZ = static_cast<float>(Slot.BottomChunkZ) * CHUNK_SIZE;
+        if (VoxelPassageGeometry::OriginLandingFloorTouchesBox(
+                VoxelBox, TopZ, BottomZ,
+                VF_BoundarySealThicknessForDefinition(*Slot.Definition),
+                OriginSpineRadius))
+        {
+            return true;
+        }
+    }
+    return false;
+}
+
 //=============================================================================
 // QUERIES
 //=============================================================================

Source/VoxelForge/Private/VoxelStrateMeasure.cpp

@@ -2863,7 +2863,8 @@ bool VF_MeasurePlayerFitWalkWithSampler(
     const FVector& AVoxel,
     const FVector& BVoxel,
     const FVoxelStrateMeasureSettings& Settings,
-    FVoxelPlayerFitWalkReport& OutReport)
+    FVoxelPlayerFitWalkReport& OutReport,
+    const TArray<FVector>* ComponentProbePoints)
 {
     using namespace VoxelStrateMeasurePrivate;
 
@@ -3038,6 +3039,28 @@ bool VF_MeasurePlayerFitWalkWithSampler(
         ? Components[Start] : INDEX_NONE;
     const int32 GoalComponent = Goal >= 0 && Components.IsValidIndex(Goal)
         ? Components[Goal] : INDEX_NONE;
+
+    if (ComponentProbePoints != nullptr)
+    {
+        OutReport.ComponentProbePlayerFit.Init(0u, ComponentProbePoints->Num());
+        OutReport.ComponentProbeInStartComponent.Init(0u, ComponentProbePoints->Num());
+        for (int32 ProbeIndex = 0; ProbeIndex < ComponentProbePoints->Num(); ++ProbeIndex)
+        {
+            int32 ProbeCell = INDEX_NONE;
+            const FVector& ProbePoint = (*ComponentProbePoints)[ProbeIndex];
+            if (!FindCellForPoint(Grid, ProbePoint, ProbeCell)
+                || !IsEligiblePlayerFitCell(Grid, PlayerFitMask, ProbeCell))
+            {
+                continue;
+            }
+            OutReport.ComponentProbePlayerFit[ProbeIndex] = 1u;
+            if (StartComponent >= 0 && Components.IsValidIndex(ProbeCell)
+                && Components[ProbeCell] == StartComponent)
+            {
+                OutReport.ComponentProbeInStartComponent[ProbeIndex] = 1u;
+            }
+        }
+    }
     if (StartComponent >= 0)
     {
         float BestOriginDistanceSquared = FLT_MAX;

Source/VoxelForge/Public/VoxelCaveMorphology.h

@@ -51,12 +51,11 @@ enum class ECaveGeneratorType : uint8;
  * A source query answer selects the landing's XY/Z anchor.  Because that pure query does not
  * flood-fill the live network, every inter-strate end also gets a deterministic root connector
  * (`bHasNetworkConnector`).  Its flat floor ramps to the same common interior root level for that
- * strate, so both mouths enter one walkable hub even when their authored floors are at opposite
- * sides of the strate.  The hub is an annular walkable network around (0,0), not the pre-existing
- * vertical air shaft.  `RootSpineRadius` keeps both the hub air and support slab outside that shaft,
- * so the spine remains open.  If the direct run would be steeper than 44 degrees, the connector
- * uses a deterministic level dog-leg before its final ramp; the bend is geometry, not a per-voxel
- * search.
+ * strate, so both mouths enter the finite landing room at (0,0) even when their authored floors
+ * are at opposite sides of the strate.  `RootSpineRadius` supplies the small endpoint overlap that
+ * joins the connector to that room; it does not create a vertical shaft.  If the direct run would
+ * be steeper than the named 15 degree tunnel contract, the connector uses a deterministic level
+ * dog-leg before its final ramp; the bend is geometry, not a per-voxel search.
  */
 struct VOXELFORGE_API FVoxelPassageLanding
 {

Source/VoxelForge/Public/VoxelDensityPrimitives.h

@@ -26,6 +26,7 @@
 
 #include "CoreMinimal.h"
 #include "VoxelTypes.h"   // SmoothStep01
+#include "VoxelPassageGeometry.h" // shared body-sized landing/tunnel geometry
 
 //=============================================================================
 // SEAL DE FRONTIÈRE / BOUNDARY SEAL
@@ -110,33 +111,97 @@ FORCEINLINE void VF_ApplyPassageLandingCarving(float& Density, float LandingSDF,
 }
 
 //=============================================================================
-// SPINE DE DESCENTE (0,0) / (0,0) DESCENT SPINE
+// LANDING ROOM ORIGINE (0,0) / ORIGIN LANDING ROOM
 //=============================================================================
-// Creuse une colonne verticale garantie ouverte au XY monde (0,0) dans l'INTÉRIEUR de la strate
-// (entre les seals haut et bas). Les seals sont laissés intacts pour que le joueur doive encore
-// creuser à travers pour descendre — ceci ne fait qu'un espace d'atterrissage propre, indépendant
-// de l'archétype, aligné à travers toutes les strates.
+// The old implementation carved a full-height cylinder. That made the origin visually open but
+// left no floor anywhere except at the bottom, so it was a fall shaft rather than a landing. The
+// origin primitive is now a top-anchored rounded room with a real flat floor in every strate.
+// It never crosses either vertical seal. The inter-strate seal remains solid until a passage (or
+// the player) opens it; there is no default vertical bore between rooms.
 FORCEINLINE void VF_ApplyOriginSpine(float& Density, float WorldX, float WorldY, float WorldZ,
     float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
 {
     if (Radius <= 0.0f) return;
 
-    // Stay within the interior — never touch the seal bands.
-    const float InnerTop = StrateTopZ - SealThickness;
-    const float InnerBot = StrateBottomZ + SealThickness;
-    if (WorldZ <= InnerBot || WorldZ >= InnerTop) return;
+    const VoxelPassageGeometry::FOriginLandingGeometry Geometry =
+        VoxelPassageGeometry::BuildOriginLandingGeometry(
+            StrateTopZ, StrateBottomZ, SealThickness, Radius);
+    if (!Geometry.bValid) return;
 
-    const float DistXY = FMath::Sqrt(WorldX * WorldX + WorldY * WorldY);
-    const float SDF = DistXY - Radius;  // < 0 inside the column
-    const float Blend = 3.0f;
-    if (SDF < Blend)
+    const float RoomSDF = VoxelPassageGeometry::OriginLandingRoomSDF(
+        FVector(WorldX, WorldY, WorldZ), Geometry);
+    VF_ApplyPassageLandingCarving(
+        Density, RoomSDF, BaseDensity, SealThickness);
+
+    // The floor is intentionally written after the room carve. It is also reasserted after the
+    // passage/disturbance posts by the callers below; doing it here makes the standalone primitive
+    // itself a complete landing-room operation.
+    if (WorldZ <= Geometry.FloorZ + KINDA_SMALL_NUMBER
+        && WorldZ > Geometry.FloorZ - Geometry.FloorThickness
+        && FMath::Abs(WorldX) <= FMath::Max(Geometry.HalfWidth - 1.0f, 0.0f)
+        && FMath::Abs(WorldY) <= FMath::Max(Geometry.HalfWidth - 1.0f, 0.0f))
     {
-        float Carve = FMath::Clamp((Blend - SDF) / (Blend * 2.0f), 0.0f, 1.0f);
-        Carve = SmoothStep01(Carve);
-        Density -= Carve * (BaseDensity * 2.0f + SealThickness);
+        Density = FMath::Max(Density, BaseDensity);
     }
 }
 
+/** Reassert only the origin-room air volume after a post-process that may add rock. */
+FORCEINLINE void VF_ApplyOriginLandingAir(float& Density,
+    float WorldX, float WorldY, float WorldZ,
+    float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
+{
+    if (Radius <= 0.0f) return;
+    const VoxelPassageGeometry::FOriginLandingGeometry Geometry =
+        VoxelPassageGeometry::BuildOriginLandingGeometry(
+            StrateTopZ, StrateBottomZ, SealThickness, Radius);
+    if (!Geometry.bValid) return;
+    const float RoomSDF = VoxelPassageGeometry::OriginLandingRoomSDF(
+        FVector(WorldX, WorldY, WorldZ), Geometry);
+    VF_ApplyPassageLandingCarving(
+        Density, RoomSDF, BaseDensity, SealThickness);
+}
+
+/** Reassert only the origin-room support slab after an air carve/post-process. */
+FORCEINLINE void VF_ApplyOriginLandingFloor(float& Density,
+    float WorldX, float WorldY, float WorldZ,
+    float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
+{
+    if (Radius <= 0.0f) return;
+    const VoxelPassageGeometry::FOriginLandingGeometry Geometry =
+        VoxelPassageGeometry::BuildOriginLandingGeometry(
+            StrateTopZ, StrateBottomZ, SealThickness, Radius);
+    if (!Geometry.bValid) return;
+    if (WorldZ <= Geometry.FloorZ + KINDA_SMALL_NUMBER
+        && WorldZ > Geometry.FloorZ - Geometry.FloorThickness
+        && FMath::Abs(WorldX) <= FMath::Max(Geometry.HalfWidth - 1.0f, 0.0f)
+        && FMath::Abs(WorldY) <= FMath::Max(Geometry.HalfWidth - 1.0f, 0.0f))
+    {
+        Density = FMath::Max(Density, BaseDensity);
+    }
+}
+
+/** MC-facing origin-room air backstop for the post-disturbance path. */
+FORCEINLINE void VF_ApplyOriginLandingAirMC(float& Density,
+    float WorldX, float WorldY, float WorldZ,
+    float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
+{
+    float InternalDensity = -Density;
+    VF_ApplyOriginLandingAir(InternalDensity, WorldX, WorldY, WorldZ,
+        StrateTopZ, StrateBottomZ, SealThickness, BaseDensity, Radius);
+    Density = -InternalDensity;
+}
+
+/** MC-facing origin-room floor backstop for the post-disturbance path. */
+FORCEINLINE void VF_ApplyOriginLandingFloorMC(float& Density,
+    float WorldX, float WorldY, float WorldZ,
+    float StrateTopZ, float StrateBottomZ, float SealThickness, float BaseDensity, float Radius)
+{
+    float InternalDensity = -Density;
+    VF_ApplyOriginLandingFloor(InternalDensity, WorldX, WorldY, WorldZ,
+        StrateTopZ, StrateBottomZ, SealThickness, BaseDensity, Radius);
+    Density = -InternalDensity;
+}
+
 //=============================================================================
 // XY EDGE SEAL / SCELLEMENT DE LA LIMITE XY
 //=============================================================================

Source/VoxelForge/Public/VoxelGenerator.h

@@ -77,9 +77,9 @@ public:
     // Les formes créatives viennent ensuite des params de strate.
     int32 Seed = 0;
 
-    // Radius (voxels) of the guaranteed open vertical landing column carved at world
-    // XY (0,0) in every strate — the (0,0) descent spine. Copied from VoxelSettings.
-    // 0 disables the spine carve.
+    // Authored radius (voxels) of the guaranteed flat-floored landing room at world XY (0,0) in
+    // every strate — the old “spine” setting now sizes a room and never creates a vertical bore.
+    // 0 disables the origin landing rooms. Copied from VoxelSettings.
     float OriginSpineRadius = 14.0f;
 
     // Radius (voxels) of the bounded world in actor-space XY, measured from (0,0).

Source/VoxelForge/Public/VoxelPassageGeometry.h

@@ -0,0 +1,308 @@
+// Shared dimensions and construction laws for walkable passages and origin landings.
+//
+// This header is deliberately free of UObjects.  The density path, the operator stack, the
+// passage generator, and the headless measurements all include the same arithmetic so a geometry
+// change cannot leave one of those paths with a different room or slope contract.
+
+#pragma once
+
+#include "CoreMinimal.h"
+
+namespace VoxelPassageGeometry
+{
+    // Authored scale and player body used by the §6.5 landing calculation.
+    constexpr float VoxelSizeMeters = 0.25f;
+    constexpr float PlayerRadiusVoxels = 34.0f / 25.0f;
+    constexpr float PlayerHalfHeightVoxels = 88.0f / 25.0f;
+    constexpr float PlayerHeightVoxels = 2.0f * PlayerHalfHeightVoxels;
+    constexpr float HeadroomVoxels = 4.0f;                 // 1 m
+    constexpr float MinimumTurnFloorWidthVoxels = 12.0f;  // 3 m
+    constexpr float MinimumLandingHalfWidthVoxels =
+        MinimumTurnFloorWidthVoxels * 0.5f;
+    constexpr float MinimumRoomHeightVoxels = 12.0f;       // 3 m
+    constexpr float LandingFloorThicknessVoxels = 3.0f;
+    constexpr float SealSafetyMarginVoxels = 4.0f;
+    constexpr float RoomRoundingVoxels = 1.5f;
+    constexpr float LandingCarveBlendVoxels = 4.0f;
+    // Level tunnel apron outside each room-floor edge.  It covers the room/tunnel SDF blend and
+    // keeps the ramp from starting while the route is still over the room's square support patch.
+    constexpr float WalkableTunnelLandingApronVoxels = 6.0f; // 1.5 m
+    // A level transition after a bend lets the route turn before its sloped segment begins.
+    constexpr float WalkableTunnelTurnTransitionVoxels = 6.0f; // 1.5 m
+    // Keep the tunnel-air post a half voxel above the authored support plane.  This is a numerical
+    // ownership band: the floor writer owns the plane, while the air writer owns the capsule
+    // volume above it even when two overlapping passage projections differ by a fraction.
+    constexpr float WalkableTunnelFloorAirClearanceVoxels = 0.5f;
+
+    // A 15 degree ramp is comfortably below the 44 degree engine walkability ceiling.  The
+    // latter is a scramble limit, not a sensible default for a tunnel the player walks through.
+    constexpr float WalkableTunnelMaxGradientDegrees = 15.0f;
+    constexpr float WalkableTunnelMaxGradient = 0.2679491924311227f; // tan(15 degrees)
+
+    // The network connector retains the §6.5 single-file dimensions: 2.5 m clear width and 3 m
+    // clear height.  These values are in voxels because all passage descriptors are voxel-space.
+    constexpr float ConnectorRadiusVoxels = 5.0f;
+    constexpr float ConnectorHeightVoxels = 12.0f;
+    constexpr float RootOverlapVoxels = 2.25f;
+
+    // The walkability contract is about the floor carried by the tube, not only its centreline.
+    // A tapered tube changes that floor by the radius delta, so the construction and the audit
+    // use this same conservative floor delta.
+    FORCEINLINE float TunnelFloorZ(const FVector& Centreline, float Radius)
+    {
+        return Centreline.Z - FMath::Abs(Radius);
+    }
+
+    FORCEINLINE float TunnelFloorGradient(
+        const FVector& Start, float StartRadius,
+        const FVector& End, float EndRadius)
+    {
+        const float HorizontalRun = FVector2D(
+            End.X - Start.X, End.Y - Start.Y).Size();
+        if (HorizontalRun <= KINDA_SMALL_NUMBER)
+        {
+            return FMath::Abs(TunnelFloorZ(End, EndRadius)
+                - TunnelFloorZ(Start, StartRadius)) > KINDA_SMALL_NUMBER
+                ? FLT_MAX : 0.0f;
+        }
+        return FMath::Abs(TunnelFloorZ(End, EndRadius)
+            - TunnelFloorZ(Start, StartRadius)) / HorizontalRun;
+    }
+
+    FORCEINLINE float RequiredHorizontalRunForFloorDrop(
+        float FirstFloorDrop, float SecondFloorDrop)
+    {
+        return 2.0f * FMath::Max(
+            FMath::Abs(FirstFloorDrop), FMath::Abs(SecondFloorDrop))
+            / WalkableTunnelMaxGradient;
+    }
+
+    /** Project a query into the nearest horizontal control segment of a walkable tunnel. */
+    FORCEINLINE bool ProjectWalkableTunnelFloor(
+        const TArray<FVector>& ControlPoints,
+        const TArray<float>& ControlRadii,
+        const FVector& Position,
+        float& OutFloorZ,
+        float& OutSupportRadius,
+        int32* OutSegmentIndex = nullptr)
+    {
+        if (OutSegmentIndex != nullptr)
+        {
+            *OutSegmentIndex = INDEX_NONE;
+        }
+        if (ControlPoints.Num() < 2
+            || ControlRadii.Num() != ControlPoints.Num())
+        {
+            return false;
+        }
+
+        const FVector2D QueryXY(Position.X, Position.Y);
+        float BestDistanceSquared = FLT_MAX;
+        bool bFoundSegment = false;
+        for (int32 SegmentIndex = 0;
+             SegmentIndex + 1 < ControlPoints.Num();
+             ++SegmentIndex)
+        {
+            const FVector& A = ControlPoints[SegmentIndex];
+            const FVector& B = ControlPoints[SegmentIndex + 1];
+            const FVector2D AXY(A.X, A.Y);
+            const FVector2D Delta = FVector2D(B.X, B.Y) - AXY;
+            const float LengthSquared = Delta.SizeSquared();
+            if (LengthSquared <= KINDA_SMALL_NUMBER)
+            {
+                continue;
+            }
+
+            const float T = FMath::Clamp(
+                FVector2D::DotProduct(QueryXY - AXY, Delta) / LengthSquared,
+                0.0f, 1.0f);
+            const FVector2D ClosestXY = AXY + Delta * T;
+            const float DistanceSquared = (QueryXY - ClosestXY).SizeSquared();
+            if (DistanceSquared >= BestDistanceSquared)
+            {
+                continue;
+            }
+
+            const float StartRadius = FMath::Abs(ControlRadii[SegmentIndex]);
+            const float EndRadius = FMath::Abs(ControlRadii[SegmentIndex + 1]);
+            OutFloorZ = FMath::Lerp(
+                TunnelFloorZ(A, StartRadius),
+                TunnelFloorZ(B, EndRadius),
+                T);
+            OutSupportRadius = FMath::Max(
+                FMath::Min(StartRadius, EndRadius) - 0.5f,
+                PlayerRadiusVoxels);
+            if (OutSegmentIndex != nullptr)
+            {
+                *OutSegmentIndex = SegmentIndex;
+            }
+            BestDistanceSquared = DistanceSquared;
+            bFoundSegment = true;
+        }
+
+        return bFoundSegment
+            && FMath::IsFinite(OutFloorZ)
+            && FMath::IsFinite(OutSupportRadius)
+            && OutSupportRadius > 0.0f
+            && BestDistanceSquared <= FMath::Square(OutSupportRadius);
+    }
+
+    struct FOriginLandingGeometry
+    {
+        bool bValid = false;
+        float FloorZ = 0.0f;
+        float CeilingZ = 0.0f;
+        float HalfWidth = 0.0f;
+        float FloorThickness = LandingFloorThicknessVoxels;
+    };
+
+    FORCEINLINE float LandingHalfWidthForRadius(float Radius)
+    {
+        const float SafeRadius = FMath::Max(FMath::Abs(Radius), 1.0f);
+        return FMath::Max(MinimumLandingHalfWidthVoxels, SafeRadius + 2.0f);
+    }
+
+    FORCEINLINE float LandingHeightForRadius(float Radius)
+    {
+        const float SafeRadius = FMath::Max(FMath::Abs(Radius), 1.0f);
+        return FMath::Max(
+            FMath::Max(MinimumRoomHeightVoxels, PlayerHeightVoxels + HeadroomVoxels),
+            2.0f * SafeRadius + 2.0f);
+    }
+
+    /**
+     * Build the one origin landing in a strate.
+     *
+     * `OriginRadius` is the old spine setting and becomes the room's authored mouth radius.  The
+     * room dimensions therefore reuse the §6.5 formula exactly:
+     *   half-width = max(7, radius + 2),
+     *   height = max(12, capsule height + 4, 2 * radius + 2).
+     * The floor is placed against the top of the safe interior interval.  This makes the first
+     * landing the place reached from above, while every lower landing remains sealed above until
+     * progression opens its inter-strate passage.
+     */
+    FORCEINLINE FOriginLandingGeometry BuildOriginLandingGeometry(
+        float StrateTopZ, float StrateBottomZ, float SealThickness, float OriginRadius)
+    {
+        FOriginLandingGeometry Result;
+        if (!(OriginRadius > 0.0f)
+            || !FMath::IsFinite(StrateTopZ)
+            || !FMath::IsFinite(StrateBottomZ)
+            || !FMath::IsFinite(SealThickness)
+            || !FMath::IsFinite(OriginRadius))
+        {
+            return Result;
+        }
+
+        Result.HalfWidth = LandingHalfWidthForRadius(OriginRadius);
+        const float DesiredHeight = LandingHeightForRadius(OriginRadius);
+        const float SafeSeal = FMath::Max(SealThickness, 0.0f);
+        const float InnerBottom = StrateBottomZ + SafeSeal;
+        const float InnerTop = StrateTopZ - SafeSeal;
+        const float MinimumFloor = InnerBottom
+            + Result.FloorThickness + SealSafetyMarginVoxels;
+        const float MaximumFloor = InnerTop
+            - DesiredHeight - SealSafetyMarginVoxels;
+        if (!FMath::IsFinite(InnerBottom) || !FMath::IsFinite(InnerTop)
+            || !(InnerTop > InnerBottom)
+            || !FMath::IsFinite(MinimumFloor)
+            || !FMath::IsFinite(MaximumFloor)
+            || MaximumFloor < MinimumFloor)
+        {
+            Result.HalfWidth = 0.0f;
+            return Result;
+        }
+
+        Result.FloorZ = MaximumFloor;
+        Result.CeilingZ = Result.FloorZ + DesiredHeight;
+        Result.bValid = true;
+        return Result;
+    }
+
+    FORCEINLINE bool IntersectsClosedInterval(float MinA, float MaxA,
+                                               float MinB, float MaxB)
+    {
+        return MaxA >= MinB && MinA <= MaxB;
+    }
+
+    /** Conservative influence box for the origin room's air carve. */
+    FORCEINLINE bool OriginLandingRoomTouchesBox(
+        const FBox& VoxelBox,
+        float StrateTopZ, float StrateBottomZ, float SealThickness, float OriginRadius)
+    {
+        if (!VoxelBox.IsValid) return false;
+        const FOriginLandingGeometry Geometry = BuildOriginLandingGeometry(
+            StrateTopZ, StrateBottomZ, SealThickness, OriginRadius);
+        if (!Geometry.bValid) return false;
+        const float Pad = LandingCarveBlendVoxels;
+        return IntersectsClosedInterval(
+                   VoxelBox.Min.X, VoxelBox.Max.X,
+                   -Geometry.HalfWidth - Pad, Geometry.HalfWidth + Pad)
+            && IntersectsClosedInterval(
+                   VoxelBox.Min.Y, VoxelBox.Max.Y,
+                   -Geometry.HalfWidth - Pad, Geometry.HalfWidth + Pad)
+            && IntersectsClosedInterval(
+                   VoxelBox.Min.Z, VoxelBox.Max.Z,
+                   Geometry.FloorZ - Pad, Geometry.CeilingZ + Pad);
+    }
+
+    /** Conservative influence box for the origin room's guaranteed solid floor. */
+    FORCEINLINE bool OriginLandingFloorTouchesBox(
+        const FBox& VoxelBox,
+        float StrateTopZ, float StrateBottomZ, float SealThickness, float OriginRadius)
+    {
+        if (!VoxelBox.IsValid) return false;
+        const FOriginLandingGeometry Geometry = BuildOriginLandingGeometry(
+            StrateTopZ, StrateBottomZ, SealThickness, OriginRadius);
+        if (!Geometry.bValid) return false;
+
+        // One voxel is a proof margin, not a write margin. It keeps ClassifyTile conservative at
+        // an exact lattice edge and mirrors the existing passage-floor guard.
+        constexpr float ProofPad = 1.0f;
+        const float FloorHalfWidth = FMath::Max(
+            Geometry.HalfWidth - 1.0f, 0.0f);
+        return IntersectsClosedInterval(
+                   VoxelBox.Min.X, VoxelBox.Max.X,
+                   -FloorHalfWidth - ProofPad, FloorHalfWidth + ProofPad)
+            && IntersectsClosedInterval(
+                   VoxelBox.Min.Y, VoxelBox.Max.Y,
+                   -FloorHalfWidth - ProofPad, FloorHalfWidth + ProofPad)
+            && IntersectsClosedInterval(
+                   VoxelBox.Min.Z, VoxelBox.Max.Z,
+                   Geometry.FloorZ - Geometry.FloorThickness - ProofPad,
+                   Geometry.FloorZ + ProofPad);
+    }
+
+    /** Signed distance for a rounded origin room with a hard flat floor. */
+    FORCEINLINE float OriginLandingRoomSDF(
+        const FVector& Position, const FOriginLandingGeometry& Geometry)
+    {
+        if (!Geometry.bValid || Geometry.CeilingZ <= Geometry.FloorZ)
+        {
+            return FLT_MAX;
+        }
+
+        const FVector Center(0.0f, 0.0f,
+            (Geometry.FloorZ + Geometry.CeilingZ) * 0.5f);
+        const float Rounding = RoomRoundingVoxels;
+        const float HalfZ = (Geometry.CeilingZ - Geometry.FloorZ) * 0.5f;
+        const FVector HalfExtent(
+            FMath::Max(Geometry.HalfWidth - Rounding, 0.25f),
+            FMath::Max(Geometry.HalfWidth - Rounding, 0.25f),
+            FMath::Max(HalfZ - Rounding, 0.25f));
+        const FVector D(
+            FMath::Abs(Position.X - Center.X) - HalfExtent.X,
+            FMath::Abs(Position.Y - Center.Y) - HalfExtent.Y,
+            FMath::Abs(Position.Z - Center.Z) - HalfExtent.Z);
+        const FVector Outside(
+            FMath::Max(D.X, 0.0f),
+            FMath::Max(D.Y, 0.0f),
+            FMath::Max(D.Z, 0.0f));
+        const float Inside = FMath::Min(
+            FMath::Max(D.X, FMath::Max(D.Y, D.Z)), 0.0f);
+        const float RoundedBoxSDF = Outside.Size() + Inside - Rounding;
+
+        // Below the floor is rock. Above it the rounded-box air volume is authoritative.
+        return FMath::Max(RoundedBoxSDF, Geometry.FloorZ - Position.Z);
+    }
+}

Source/VoxelForge/Public/VoxelSettings.h

@@ -392,10 +392,11 @@ public:
 	// SPINE & INTER-STRATE CONNECTIONS  (the (0,0) descent axis)
 	//=========================================================================
 
-	// Radius (voxels) of the guaranteed open vertical "landing" column carved at
-	// world XY (0,0) in EVERY strate, regardless of archetype. This is the prepared
-	// space the player digs THROUGH the seal into when descending. 0 = disabled.
-	//   10-14 → cozy shaft (default) · 20+ → wide landing chamber
+    // Authored radius (voxels) of the guaranteed (0,0) landing room in EVERY strate, regardless
+    // of archetype. The §6.5 body-sized formulas turn it into a flat-floored room; this setting
+    // no longer bores a vertical column. 0 = disabled. The room is top-anchored inside each
+    // strate, and the seals remain solid until a progression passage is opened.
+    //   10-14 → compact landing room (default) · 20+ → broad landing room
 	UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Voxel|Spine", meta = (ClampMin = "0.0"))
 	float OriginSpineRadius = 14.0f;
 

Source/VoxelForge/Public/VoxelStrateDefinition.h

@@ -211,9 +211,11 @@ public:
     //=========================================================================
     // INTER-STRATE PASSAGES (how THIS strate connects DOWN to the next)
     //=========================================================================
-    // Auto-carved descent tunnels from this strate to the one below it: count, style
-    // (straight / worm / spiral / cascade), tapered width, length, placement. The (0,0)
-    // spine descent is separate (player-dug); these are the extra shortcuts.
+    // Auto-carved passages from this strate to the one below it: count, style
+    // (walkable sloped tunnel / worm / spiral / cascade), tapered width, length, placement.
+    // Every strate has its own finite (0,0) landing room; the passage opens the next room through
+    // progression. The non-default styles are retained as exotic, non-walkability-guaranteed
+    // descriptors.
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Strate|Passages")
     FStratePassageConfig PassageConfig;
 

Source/VoxelForge/Public/VoxelStrateManager.h

@@ -66,18 +66,17 @@ struct FVoxelPassage
     FVector RequestedLowerPoint = FVector::ZeroVector;
 
     // Passage dimensions — how wide the carved tunnel is (in voxels).
-    // Varies by type: VerticalShaft ~7-8, SpiralDescent ~4, CrackCrevice ~2-3, others ~5.
+    // The default SlopedTunnel is a single-file 2.5 m clear bore at its narrowest point;
+    // authored exotic styles retain their own widths and are not covered by the walkable law.
     float Radius = 5.0f;
 
     // The shape/style of this passage. Determines how control points are generated
     // and how the passage feels to navigate (shaft, spiral, ledges, crack, etc.).
     EVoxelPassageType PassageType = EVoxelPassageType::SlopedTunnel;
 
-    // Multi-segment control points for complex passage shapes.
-    // Used by SpiralDescent (helix points) and CascadingDrops (ledge+drop points).
-    // When non-empty, the SDF evaluator walks this array as a capsule chain
-    // instead of using Upper→Mid→Lower logic.
-    // Empty for simple types (SlopedTunnel, VerticalShaft, CrackCrevice).
+    // Multi-segment control points for passage shapes. The default SlopedTunnel contains the two
+    // gentle ramp legs of its deterministic switchback; exotic styles retain their authored chain.
+    // When non-empty, the SDF evaluator walks this array as a capsule chain.
     TArray<FVector> ControlPoints;
 
     // Per-control-point tube radius (parallel to ControlPoints) for tapered tunnels —
@@ -90,6 +89,16 @@ struct FVoxelPassage
     FVoxelPassageLanding UpperLanding;
     FVoxelPassageLanding LowerLanding;
 
+    // Construction-time walkability facts for diagnostics and the commandlet report. These are
+    // metadata, not a second runtime decision: the final-density sampler remains authoritative.
+    bool bWalkableTunnelContract = false;
+    float TunnelMaxGradientDegrees = 0.0f;
+    float TunnelVerticalDropVoxels = 0.0f;
+    float TunnelRequiredHorizontalRunVoxels = 0.0f;
+    float TunnelHorizontalPathLengthVoxels = 0.0f;
+    float TunnelMinimumClearWidthVoxels = 0.0f;
+    float TunnelClearHeightVoxels = 0.0f;
+
     // Bounding sphere enclosing the whole passage (+ radius + blend), in voxel coords.
     // Computed once in GeneratePassages; lets EvaluateModifierSDF reject far voxels with
     // a single squared-distance test instead of walking every segment per voxel.
@@ -362,14 +371,26 @@ public:
     void ApplyPassageLandingAir(float& Density, float WorldX, float WorldY, float WorldZ,
                                 float BaseDensity, float SealThickness) const;
 
+    /** Reassert the default walkable tunnel's clear air in internal density after any post. */
+    void ApplyPassageTunnelAir(float& Density, float WorldX, float WorldY, float WorldZ,
+                               float BaseDensity, float SealThickness) const;
+
     /** Re-assert landing air after MC-space disturbances, still before the final XY seal. */
     void ApplyPassageLandingAirMC(float& Density, float WorldX, float WorldY, float WorldZ,
                                   float BaseDensity, float SealThickness) const;
 
+    /** Re-assert walkable tunnel air after MC-space disturbances, still before the final XY seal. */
+    void ApplyPassageTunnelAirMC(float& Density, float WorldX, float WorldY, float WorldZ,
+                                 float BaseDensity, float SealThickness) const;
+
     /** Re-assert a landing floor after the landing air pass, still before the final XY seal. */
     void ApplyPassageLandingFloorMC(float& Density, float WorldX, float WorldY, float WorldZ,
                                     float BaseDensity) const;
 
+    /** Re-assert only the flat room floors after the tunnel-air post; never writes tunnel floors. */
+    void ApplyPassageLandingRoomFloorMC(float& Density, float WorldX, float WorldY, float WorldZ,
+                                        float BaseDensity) const;
+
     /**
      * True si la sphère englobante d'un passage (élargie du rayon de blend de carve) touche la
      * boîte VOXEL [MinVoxel, MaxVoxel]. Test conservatif O(Passages) — utilisé par ClassifyTile
@@ -380,6 +401,10 @@ public:
     /** Conservative box guard for the floor fill; unlike a tube it can affect the all-air proof. */
     bool AnyPassageLandingFloorNearBox(const FVector& MinVoxel, const FVector& MaxVoxel) const;
 
+    /** Conservative box guards for the per-strate (0,0) landing rooms and their floor slabs. */
+    bool AnyOriginLandingNearBox(const FVector& MinVoxel, const FVector& MaxVoxel) const;
+    bool AnyOriginLandingFloorNearBox(const FVector& MinVoxel, const FVector& MaxVoxel) const;
+
     /** Get all generated passages (for debug display). */
     const TArray<FVoxelPassage>& GetPassages() const { return Passages; }
 
@@ -411,12 +436,12 @@ protected:
     // World seed (stored for passage generation)
     int32 CachedSeed = 0;
 
-    // Whether to auto-open the (0,0) entry shaft through the top of strate 0.
+    // Whether to auto-open the (0,0) origin landing room from above in strate 0.
     // Copied from VoxelSettings::bOpenSurfaceEntry during Initialize().
     bool bOpenSurfaceEntry = true;
 
-    // Radius (voxels) of the surface entry shaft at (0,0). Copied from
-    // VoxelSettings::OriginSpineRadius so the entry matches the spine landing.
+    // Authored radius (voxels) of the origin landing room and its optional surface opening.
+    // Copied from VoxelSettings::OriginSpineRadius.
     float OriginSpineRadius = 14.0f;
 
     // Solid-bedrock gap between consecutive strates, in chunks. Copied from

Source/VoxelForge/Public/VoxelStrateMeasure.h

@@ -3,6 +3,7 @@
 #pragma once
 
 #include "CoreMinimal.h"
+#include "VoxelPassageGeometry.h"
 
 class UVoxelGenerator;
 class UVoxelStrateManager;
@@ -19,7 +20,7 @@ class UVoxelStrateManager;
 struct VOXELFORGE_API FVoxelPlayerCapsuleConstants
 {
     static constexpr float VoxelSizeCentimeters = 25.0f;
-    static constexpr float VoxelSizeMeters = VoxelSizeCentimeters / 100.0f;
+    static constexpr float VoxelSizeMeters = VoxelPassageGeometry::VoxelSizeMeters;
     static constexpr float RadiusCentimeters = 34.0f;
     static constexpr float HalfHeightCentimeters = 88.0f;
     // UCharacterMovementComponent's UE 5.7 default. Callers that have a character CDO should
@@ -29,9 +30,9 @@ struct VOXELFORGE_API FVoxelPlayerCapsuleConstants
     // UE 5.7's WalkableFloorZ=0.71 resolves to about 44.8 degrees; a character CDO may expose
     // the precise angle. The diagnosis test copies that precise project value when available.
     static constexpr float WalkableFloorAngleDegrees = 44.8f;
-    static constexpr float RadiusVoxels = RadiusCentimeters / VoxelSizeCentimeters;
-    static constexpr float HalfHeightVoxels = HalfHeightCentimeters / VoxelSizeCentimeters;
-    static constexpr float HeightVoxels = 2.0f * HalfHeightVoxels;
+    static constexpr float RadiusVoxels = VoxelPassageGeometry::PlayerRadiusVoxels;
+    static constexpr float HalfHeightVoxels = VoxelPassageGeometry::PlayerHalfHeightVoxels;
+    static constexpr float HeightVoxels = VoxelPassageGeometry::PlayerHeightVoxels;
 };
 
 /** Read-only density source used by the offline Tier 2 pass for a materialised custom stack. */
@@ -68,7 +69,8 @@ struct VOXELFORGE_API FVoxelStrateMeasureSettings
     TOptional<FVector2D> CoverPointA;
     TOptional<FVector2D> CoverPointB;
     float CoverMarginVoxels = 48.0f;
-    // Origin-rooted topologies can route from one mouth to the other through the (0,0) spine.
+    // Origin-rooted topologies can route from one mouth to the other through the finite (0,0)
+    // landing room and its explicitly carved connector network.
     // When true, include (0,0) in the fitted AABB before applying MaxCells. A caller must keep
     // this enabled for that topology; an over-cap route window is then refused honestly instead
     // of being cropped back to a mouth-only box.
@@ -322,6 +324,12 @@ struct VOXELFORGE_API FVoxelPlayerFitWalkReport
     int64 DepartureComponentCells = 0;
     float MouthComponentGapVoxels = -1.0f;
 
+    // Optional room probes evaluated against this same grid and start component.  The arrays are
+    // empty for ordinary callers; when supplied, each entry is 1 only when the probe is both a
+    // player-fit cell and in the arrival/start component.
+    TArray<uint8> ComponentProbePlayerFit;
+    TArray<uint8> ComponentProbeInStartComponent;
+
     // The DFS returns to its root when the target component is unreachable.  Keep both the
     // physical end of that walk and the last newly reached pose: the latter is the useful
     // failure-frontier point for a render, while the former is the literal final pose.
@@ -496,4 +504,5 @@ VOXELFORGE_API bool VF_MeasurePlayerFitWalkWithSampler(
     const FVector& AVoxel,
     const FVector& BVoxel,
     const FVoxelStrateMeasureSettings& Settings,
-    FVoxelPlayerFitWalkReport& OutReport);
+    FVoxelPlayerFitWalkReport& OutReport,
+    const TArray<FVector>* ComponentProbePoints = nullptr);

Source/VoxelForge/Public/VoxelStrateTypes.h

@@ -32,19 +32,18 @@ class AActor;                  // IWYU : paramètre de TSubclassOf seulement / T
  * of the carved tunnel (control point layout, radius, overall feel).
  *
  * Types:
- *   SlopedTunnel   — Angled bore with a horizontal midpoint offset (default/legacy).
- *   VerticalShaft  — Straight or near-straight drop between strates.
- *   SpiralDescent  — Helical corkscrew path winding downward.
- *   CascadingDrops — Series of short vertical pits connected by horizontal ledges.
- *   CrackCrevice   — Narrow fracture passage, tight squeeze through rock.
+ *   SlopedTunnel   — The default walkable, gentle-gradient tunnel between landing rooms.
+ *   VerticalShaft  — A vertical drop; never a continuous walkable descent.
+ *   SpiralDescent  — An exotic helix; walkability requires a separately designed ramp contract.
+ *   CascadingDrops — Drops and ledges; never a continuous walkable descent as authored.
+ *   CrackCrevice   — A narrow fracture; no player-fit guarantee.
  */
 UENUM(BlueprintType)
 enum class EVoxelPassageType : uint8
 {
-    // Angled bore connecting two layers with a horizontal midpoint offset.
-    // Two capsule segments: Upper→Mid, Mid→Lower. Comfortable radius (~5 voxels).
-    // This is the original passage type — feels like a natural sloped tunnel.
-    SlopedTunnel    UMETA(DisplayName = "Sloped Tunnel (angled bore)"),
+    // Walkable single-file tunnel. The runtime builds a deterministic switchback whose each ramp
+    // is below VoxelPassageGeometry::WalkableTunnelMaxGradientDegrees.
+    SlopedTunnel    UMETA(DisplayName = "Sloped Tunnel (walkable default)"),
 
     // Straight vertical drop between strates. Same XY for upper and lower points.
     // Wider radius (~7-8 voxels) to feel like a natural shaft or sinkhole.
@@ -1758,7 +1757,9 @@ struct VOXELFORGE_API FStrateDisturbanceParams
 UENUM(BlueprintType)
 enum class EVoxelPassageStyle : uint8
 {
-    Straight  UMETA(DisplayName = "Straight (vertical shaft)"),
+    // “Straight” is retained as the authored style name for the base connection, but its runtime
+    // geometry is a gentle two-leg switchback rather than a vertical shaft.
+    Straight  UMETA(DisplayName = "Straight (walkable sloped tunnel)"),
     Worm      UMETA(DisplayName = "Worm (organic meander around the axis)"),
     Spiral    UMETA(DisplayName = "Spiral (corkscrew descent)"),
     Cascading UMETA(DisplayName = "Cascading (ledge + drop staircase)")
@@ -1768,8 +1769,8 @@ enum class EVoxelPassageStyle : uint8
  * FStratePassageConfig — how THIS strate connects DOWN to the strate below it.
  *
  * Lives on each UVoxelStrateDefinition: the upper strate of every boundary controls its
- * own descent tunnels, so different layers connect differently. The (0,0) spine descent
- * is separate (player-dug); these are the auto-carved shortcuts placed away from it.
+ * own progression tunnel, so different layers connect differently. Each strate has a finite
+ * (0,0) landing room; this config controls the passage that opens the next room.
  */
 USTRUCT(BlueprintType)
 struct VOXELFORGE_API FStratePassageConfig
@@ -1782,17 +1783,19 @@ struct VOXELFORGE_API FStratePassageConfig
 
     // Tunnel shape.
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Passage")
-    EVoxelPassageStyle Style = EVoxelPassageStyle::Worm;
+    EVoxelPassageStyle Style = EVoxelPassageStyle::Straight;
 
     // ----- WIDTH (tapers along the length) -----
     // Radius at the two mouths (entry/exit) and at the middle. Equal = uniform tube;
-    // The defaults are 2 m radius / 4 m bore at mouths and 1.5 m radius / 3 m bore in the middle.
+    // The walkable default is deliberately single-file: 3.0 m diameter at mouths and 2.5 m at
+    // the waist (6/5 voxel radii at 25 cm per voxel). The §6.5 landing room remains wider for
+    // turning.
     // Mouth > Mid = chambers at the ends with a squeeze between; Mid > Mouth = a bulge.
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Passage|Width", meta = (ClampMin = "1.0"))
-    float MouthRadius = 8.0f;
+    float MouthRadius = 6.0f;
 
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Passage|Width", meta = (ClampMin = "1.0"))
-    float MidRadius = 6.0f;
+    float MidRadius = 5.0f;
 
     // ----- LENGTH -----
     // How far the tunnel reaches INTO each strate (voxels). Auto-capped to the interior;
@@ -1813,7 +1816,8 @@ struct VOXELFORGE_API FStratePassageConfig
     float DistanceMax = 192.0f;
 
     // ----- SHAPE detail -----
-    // Worm: max sideways excursion from the axis (voxels). 24 = 6 m; 0 = straight even in Worm style.
+    // Exotic styles only: max sideways excursion from the axis (voxels). 24 = 6 m; 0 = straight
+    // even in Worm style. The default walkable switchback does not use this wander value.
     UPROPERTY(EditAnywhere, BlueprintReadWrite, Category = "Passage|Shape", meta = (ClampMin = "0.0"))
     float Wander = 24.0f;
 

Source/VoxelForgeEditor/Private/VoxelForgeExploreCommandlet.cpp

@@ -384,7 +384,10 @@ struct FExploreWorld
                 Index));
             Definition->StrateDescription = FText::FromString(
                 TEXT("Transient, deterministic commandlet definition."));
-            Definition->StrateHeightInChunks = 8;
+            // The commandlet's acceptance sweep uses the owner-facing base spacing:
+            // 4 chunks * 32 voxels * 0.25 m = 32 m per strate. Production assets may be taller;
+            // this keeps the measured tunnel arithmetic tied to the stated ~32 m descent.
+            Definition->StrateHeightInChunks = 4;
             Definition->TransitionType = EVoxelStrateTransition::Hard;
             Definition->GeneratorType = Index == Arguments.Slot
                 ? Arguments.Archetype
@@ -510,6 +513,12 @@ struct FExploreWalkOutput
     bool bOriginCheckAvailable = false;
     FString OriginCheckRefusalReason;
     FVoxelPlayerFitWalkReport OriginCheckReport;
+    int32 ArrivalLandingRoomProbeCount = 0;
+    int32 ArrivalLandingRoomPlayerFitProbeCount = 0;
+    int32 ArrivalLandingRoomArrivalComponentProbeCount = 0;
+    int32 DepartureLandingRoomProbeCount = 0;
+    int32 DepartureLandingRoomPlayerFitProbeCount = 0;
+    int32 DepartureLandingRoomArrivalComponentProbeCount = 0;
 };
 
 struct FExploreExportOutput
@@ -542,12 +551,16 @@ bool FindMouths(
     FVector& OutArrival,
     FVector& OutDeparture,
     int32& OutArrivalCount,
-    int32& OutDepartureCount)
+    int32& OutDepartureCount,
+    const FVoxelPassage*& OutArrivalPassage,
+    const FVoxelPassage*& OutDeparturePassage)
 {
     OutArrival = FVector::ZeroVector;
     OutDeparture = FVector::ZeroVector;
     OutArrivalCount = 0;
     OutDepartureCount = 0;
+    OutArrivalPassage = nullptr;
+    OutDeparturePassage = nullptr;
     for (const FVoxelPassage& Passage : Manager.GetPassages())
     {
         if (Passage.LowerStrateIndex == TargetSlot
@@ -556,6 +569,7 @@ bool FindMouths(
             if (OutArrivalCount == 0)
             {
                 OutArrival = Passage.LowerPoint;
+                OutArrivalPassage = &Passage;
             }
             ++OutArrivalCount;
         }
@@ -565,6 +579,7 @@ bool FindMouths(
             if (OutDepartureCount == 0)
             {
                 OutDeparture = Passage.UpperPoint;
+                OutDeparturePassage = &Passage;
             }
             ++OutDepartureCount;
         }
@@ -1273,13 +1288,17 @@ bool RunWalk(
         return false;
     }
 
+    const FVoxelPassage* ArrivalPassage = nullptr;
+    const FVoxelPassage* DeparturePassage = nullptr;
     if (!FindMouths(
             *World.Manager,
             Arguments.Slot,
             OutOutput.ArrivalVoxels,
             OutOutput.DepartureVoxels,
             OutOutput.ArrivalPassageCount,
-            OutOutput.DeparturePassageCount))
+            OutOutput.DeparturePassageCount,
+            ArrivalPassage,
+            DeparturePassage))
     {
         OutOutput.Status = TEXT("refused");
         OutOutput.RefusalReason = TEXT(
@@ -1299,6 +1318,32 @@ bool RunWalk(
         Settings.PlayerCapsuleRadiusVoxels) + 2.0f;
     Settings.bIncludeOriginInCoverWindow = NeedsOriginInWindow(Arguments.Archetype);
 
+    TArray<FVector> LandingRoomProbePoints;
+    auto AppendLandingRoomProbes = [&LandingRoomProbePoints](
+        const FVoxelPassageLanding& Landing)
+    {
+        const float ProbeOffset = FMath::Min(
+            2.0f,
+            FMath::Max(0.0f, Landing.HalfWidth - 2.0f));
+        LandingRoomProbePoints.Add(Landing.StandingPoint);
+        LandingRoomProbePoints.Add(
+            Landing.StandingPoint + FVector(ProbeOffset, 0.0f, 0.0f));
+        LandingRoomProbePoints.Add(
+            Landing.StandingPoint + FVector(-ProbeOffset, 0.0f, 0.0f));
+        LandingRoomProbePoints.Add(
+            Landing.StandingPoint + FVector(0.0f, ProbeOffset, 0.0f));
+        LandingRoomProbePoints.Add(
+            Landing.StandingPoint + FVector(0.0f, -ProbeOffset, 0.0f));
+    };
+    if (ArrivalPassage != nullptr)
+    {
+        AppendLandingRoomProbes(ArrivalPassage->LowerLanding);
+    }
+    if (DeparturePassage != nullptr)
+    {
+        AppendLandingRoomProbes(DeparturePassage->UpperLanding);
+    }
+
     const FGeneratorDensitySampler Sampler(*World.Generator);
     if (!VF_MeasurePlayerFitWalkWithSampler(
             Sampler,
@@ -1308,7 +1353,8 @@ bool RunWalk(
             OutOutput.ArrivalVoxels,
             OutOutput.DepartureVoxels,
             Settings,
-            OutOutput.Report))
+            OutOutput.Report,
+            &LandingRoomProbePoints))
     {
         OutOutput.Status = TEXT("refused");
         OutOutput.RefusalReason = OutOutput.Report.RefusalReason;
@@ -1338,6 +1384,30 @@ bool RunWalk(
     {
         OutOutput.OriginCheckRefusalReason = OutOutput.OriginCheckReport.RefusalReason;
     }
+    const int32 ArrivalProbeCount = ArrivalPassage != nullptr ? 5 : 0;
+    const int32 DepartureProbeCount = DeparturePassage != nullptr ? 5 : 0;
+    OutOutput.ArrivalLandingRoomProbeCount = ArrivalProbeCount;
+    OutOutput.DepartureLandingRoomProbeCount = DepartureProbeCount;
+    for (int32 ProbeIndex = 0; ProbeIndex < OutOutput.Report.ComponentProbePlayerFit.Num();
+         ++ProbeIndex)
+    {
+        const bool bPlayerFit = OutOutput.Report.ComponentProbePlayerFit[ProbeIndex] != 0u;
+        const bool bInArrivalComponent =
+            OutOutput.Report.ComponentProbeInStartComponent.IsValidIndex(ProbeIndex)
+            && OutOutput.Report.ComponentProbeInStartComponent[ProbeIndex] != 0u;
+        if (ProbeIndex < ArrivalProbeCount)
+        {
+            OutOutput.ArrivalLandingRoomPlayerFitProbeCount += bPlayerFit ? 1 : 0;
+            OutOutput.ArrivalLandingRoomArrivalComponentProbeCount +=
+                bInArrivalComponent ? 1 : 0;
+        }
+        else
+        {
+            OutOutput.DepartureLandingRoomPlayerFitProbeCount += bPlayerFit ? 1 : 0;
+            OutOutput.DepartureLandingRoomArrivalComponentProbeCount +=
+                bInArrivalComponent ? 1 : 0;
+        }
+    }
 
     OutOutput.Status = TEXT("ok");
     return true;
@@ -1509,7 +1579,7 @@ FString BuildManifestJson(
     TSharedRef<FExploreJsonWriter> Writer =
         TJsonWriterFactory<TCHAR, TCondensedJsonPrintPolicy<TCHAR>>::Create(&Json);
     Writer->WriteObjectStart();
-    Writer->WriteValue(TEXT("schema_version"), 1);
+    Writer->WriteValue(TEXT("schema_version"), 2);
     Writer->WriteValue(TEXT("format"), TEXT("OBJ"));
     Writer->WriteValue(TEXT("mesh_file"), Export.MeshFileName);
     Writer->WriteValue(TEXT("mesh_positions_units"), TEXT("metres"));
@@ -1703,7 +1773,7 @@ FString BuildExploreJson(
     TSharedRef<FExploreJsonWriter> Writer =
         TJsonWriterFactory<TCHAR, TCondensedJsonPrintPolicy<TCHAR>>::Create(&Json);
     Writer->WriteObjectStart();
-    Writer->WriteValue(TEXT("schema_version"), 1);
+    Writer->WriteValue(TEXT("schema_version"), 2);
     Writer->WriteValue(TEXT("tool"), TEXT("VoxelForgeExplore"));
     Writer->WriteValue(TEXT("read_only_generation"), true);
 
@@ -1780,6 +1850,11 @@ FString BuildExploreJson(
     if (Arguments.bWalk)
     {
         const FVoxelPlayerFitWalkReport& Report = Output.Walk.Report;
+        // The primary report is the mouth-sized arrival/departure window.  Origin reachability is
+        // a separate, explicitly origin-inclusive measurement; expose that report at the legacy
+        // top-level keys so a sweep cannot accidentally count a window that omitted (0,0).
+        const FVoxelPlayerFitWalkReport& OriginReport = Output.Walk.bOriginCheckAvailable
+            ? Output.Walk.OriginCheckReport : Report;
         Writer->WriteObjectStart(TEXT("walk"));
         Writer->WriteValue(TEXT("status"), Output.Walk.Status);
         Writer->WriteValue(TEXT("refusal_or_error"), Output.Walk.RefusalReason);
@@ -1795,6 +1870,27 @@ FString BuildExploreJson(
         Writer->WriteValue(TEXT("working_memory_cap_bytes"), MaxWalkWorkingBytes);
         Writer->WriteValue(TEXT("arrival_passage_count"), Output.Walk.ArrivalPassageCount);
         Writer->WriteValue(TEXT("departure_passage_count"), Output.Walk.DeparturePassageCount);
+        Writer->WriteValue(TEXT("landing_room_probe_offsets_voxels"), 2.0);
+        Writer->WriteValue(TEXT("arrival_landing_room_probe_count"),
+            Output.Walk.ArrivalLandingRoomProbeCount);
+        Writer->WriteValue(TEXT("arrival_landing_room_player_fit_probe_count"),
+            Output.Walk.ArrivalLandingRoomPlayerFitProbeCount);
+        Writer->WriteValue(TEXT("arrival_landing_room_arrival_component_probe_count"),
+            Output.Walk.ArrivalLandingRoomArrivalComponentProbeCount);
+        Writer->WriteValue(TEXT("arrival_landing_room_in_arrival_component"),
+            Output.Walk.ArrivalLandingRoomProbeCount > 0
+            && Output.Walk.ArrivalLandingRoomArrivalComponentProbeCount
+                == Output.Walk.ArrivalLandingRoomProbeCount);
+        Writer->WriteValue(TEXT("departure_landing_room_probe_count"),
+            Output.Walk.DepartureLandingRoomProbeCount);
+        Writer->WriteValue(TEXT("departure_landing_room_player_fit_probe_count"),
+            Output.Walk.DepartureLandingRoomPlayerFitProbeCount);
+        Writer->WriteValue(TEXT("departure_landing_room_arrival_component_probe_count"),
+            Output.Walk.DepartureLandingRoomArrivalComponentProbeCount);
+        Writer->WriteValue(TEXT("departure_landing_room_in_arrival_component"),
+            Output.Walk.DepartureLandingRoomProbeCount > 0
+            && Output.Walk.DepartureLandingRoomArrivalComponentProbeCount
+                == Output.Walk.DepartureLandingRoomProbeCount);
         if (Output.Walk.bHasArrival)
         {
             WriteJsonVector(*Writer, TEXT("arrival_mouth_voxels"), Output.Walk.ArrivalVoxels, 1.0f);
@@ -1870,14 +1966,16 @@ FString BuildExploreJson(
         Writer->WriteValue(TEXT("agent_to_target_component_gap_m"),
             static_cast<double>(Report.AgentToTargetComponentGapVoxels)
                 * FVoxelPlayerCapsuleConstants::VoxelSizeMeters);
-        Writer->WriteValue(TEXT("origin_column_in_sampled_window"), Report.bOriginColumnInSampledWindow);
-        Writer->WriteValue(TEXT("origin_column_has_player_fit"), Report.bOriginColumnHasPlayerFit);
-        Writer->WriteValue(TEXT("origin_column_player_fit_cells"), Report.OriginColumnPlayerFitCells);
-        Writer->WriteValue(TEXT("origin_column_reachable_from_arrival"), Report.bOriginColumnReachable);
+        Writer->WriteValue(TEXT("origin_column_measurement_window"),
+            TEXT("origin-inclusive mouth-AABB + margin"));
+        Writer->WriteValue(TEXT("origin_column_in_sampled_window"), OriginReport.bOriginColumnInSampledWindow);
+        Writer->WriteValue(TEXT("origin_column_has_player_fit"), OriginReport.bOriginColumnHasPlayerFit);
+        Writer->WriteValue(TEXT("origin_column_player_fit_cells"), OriginReport.OriginColumnPlayerFitCells);
+        Writer->WriteValue(TEXT("origin_column_reachable_from_arrival"), OriginReport.bOriginColumnReachable);
         Writer->WriteValue(TEXT("reachable_set_to_origin_column_voxels"),
-            static_cast<double>(Report.ReachableSetToOriginColumnVoxels));
+            static_cast<double>(OriginReport.ReachableSetToOriginColumnVoxels));
         Writer->WriteValue(TEXT("reachable_set_to_origin_column_m"),
-            static_cast<double>(Report.ReachableSetToOriginColumnVoxels)
+            static_cast<double>(OriginReport.ReachableSetToOriginColumnVoxels)
                 * FVoxelPlayerCapsuleConstants::VoxelSizeMeters);
         Writer->WriteObjectStart(TEXT("origin_check"));
         Writer->WriteValue(TEXT("attempted"), Output.Walk.bOriginCheckAttempted);
@@ -1885,40 +1983,40 @@ FString BuildExploreJson(
         Writer->WriteValue(TEXT("refusal_or_error"), Output.Walk.OriginCheckRefusalReason);
         if (Output.Walk.bOriginCheckAvailable)
         {
-            const FVoxelPlayerFitWalkReport& OriginReport = Output.Walk.OriginCheckReport;
+            const FVoxelPlayerFitWalkReport& OriginCheckReport = Output.Walk.OriginCheckReport;
             Writer->WriteValue(TEXT("window_policy"), TEXT("origin-inclusive mouth-AABB + margin"));
-            Writer->WriteValue(TEXT("connectivity_result"), ConnectivityResultName(OriginReport.Result));
-            Writer->WriteValue(TEXT("can_reach_departure"), OriginReport.bCanReachDeparture);
-            Writer->WriteValue(TEXT("sampled_num_x"), OriginReport.SampledNumX);
-            Writer->WriteValue(TEXT("sampled_num_y"), OriginReport.SampledNumY);
-            Writer->WriteValue(TEXT("sampled_num_z"), OriginReport.SampledNumZ);
-            Writer->WriteValue(TEXT("sampled_min_x"), static_cast<double>(OriginReport.SampledMinX));
-            Writer->WriteValue(TEXT("sampled_max_x_exclusive"), static_cast<double>(OriginReport.SampledMaxX));
-            Writer->WriteValue(TEXT("sampled_min_y"), static_cast<double>(OriginReport.SampledMinY));
-            Writer->WriteValue(TEXT("sampled_max_y_exclusive"), static_cast<double>(OriginReport.SampledMaxY));
-            Writer->WriteValue(TEXT("sampled_min_z"), OriginReport.SampledMinZ);
-            Writer->WriteValue(TEXT("sampled_max_z_exclusive"), OriginReport.SampledMaxZ);
-            Writer->WriteValue(TEXT("player_fit_cells"), OriginReport.PlayerFitVolumeCells);
-            Writer->WriteValue(TEXT("reachable_player_fit_cells"), OriginReport.ReachablePlayerFitCells);
+            Writer->WriteValue(TEXT("connectivity_result"), ConnectivityResultName(OriginCheckReport.Result));
+            Writer->WriteValue(TEXT("can_reach_departure"), OriginCheckReport.bCanReachDeparture);
+            Writer->WriteValue(TEXT("sampled_num_x"), OriginCheckReport.SampledNumX);
+            Writer->WriteValue(TEXT("sampled_num_y"), OriginCheckReport.SampledNumY);
+            Writer->WriteValue(TEXT("sampled_num_z"), OriginCheckReport.SampledNumZ);
+            Writer->WriteValue(TEXT("sampled_min_x"), static_cast<double>(OriginCheckReport.SampledMinX));
+            Writer->WriteValue(TEXT("sampled_max_x_exclusive"), static_cast<double>(OriginCheckReport.SampledMaxX));
+            Writer->WriteValue(TEXT("sampled_min_y"), static_cast<double>(OriginCheckReport.SampledMinY));
+            Writer->WriteValue(TEXT("sampled_max_y_exclusive"), static_cast<double>(OriginCheckReport.SampledMaxY));
+            Writer->WriteValue(TEXT("sampled_min_z"), OriginCheckReport.SampledMinZ);
+            Writer->WriteValue(TEXT("sampled_max_z_exclusive"), OriginCheckReport.SampledMaxZ);
+            Writer->WriteValue(TEXT("player_fit_cells"), OriginCheckReport.PlayerFitVolumeCells);
+            Writer->WriteValue(TEXT("reachable_player_fit_cells"), OriginCheckReport.ReachablePlayerFitCells);
             Writer->WriteValue(TEXT("reachable_player_fit_fraction"),
-                static_cast<double>(OriginReport.ReachablePlayerFitFraction));
-            Writer->WriteValue(TEXT("player_fit_components"), OriginReport.PlayerFitComponents);
-            Writer->WriteValue(TEXT("arrival_component_cells"), OriginReport.ArrivalComponentCells);
-            Writer->WriteValue(TEXT("departure_component_cells"), OriginReport.DepartureComponentCells);
+                static_cast<double>(OriginCheckReport.ReachablePlayerFitFraction));
+            Writer->WriteValue(TEXT("player_fit_components"), OriginCheckReport.PlayerFitComponents);
+            Writer->WriteValue(TEXT("arrival_component_cells"), OriginCheckReport.ArrivalComponentCells);
+            Writer->WriteValue(TEXT("departure_component_cells"), OriginCheckReport.DepartureComponentCells);
             Writer->WriteValue(TEXT("mouth_component_gap_voxels"),
-                static_cast<double>(OriginReport.MouthComponentGapVoxels));
+                static_cast<double>(OriginCheckReport.MouthComponentGapVoxels));
             Writer->WriteValue(TEXT("origin_column_in_sampled_window"),
-                OriginReport.bOriginColumnInSampledWindow);
+                OriginCheckReport.bOriginColumnInSampledWindow);
             Writer->WriteValue(TEXT("origin_column_has_player_fit"),
-                OriginReport.bOriginColumnHasPlayerFit);
+                OriginCheckReport.bOriginColumnHasPlayerFit);
             Writer->WriteValue(TEXT("origin_column_player_fit_cells"),
-                OriginReport.OriginColumnPlayerFitCells);
+                OriginCheckReport.OriginColumnPlayerFitCells);
             Writer->WriteValue(TEXT("origin_column_reachable_from_arrival"),
-                OriginReport.bOriginColumnReachable);
+                OriginCheckReport.bOriginColumnReachable);
             Writer->WriteValue(TEXT("reachable_set_to_origin_column_voxels"),
-                static_cast<double>(OriginReport.ReachableSetToOriginColumnVoxels));
+                static_cast<double>(OriginCheckReport.ReachableSetToOriginColumnVoxels));
             Writer->WriteValue(TEXT("reachable_set_to_origin_column_m"),
-                static_cast<double>(OriginReport.ReachableSetToOriginColumnVoxels)
+                static_cast<double>(OriginCheckReport.ReachableSetToOriginColumnVoxels)
                     * FVoxelPlayerCapsuleConstants::VoxelSizeMeters);
         }
         Writer->WriteObjectEnd();