acdream/src/AcDream.Core/Physics/PhysicsDataCache.cs

using System.Collections.Concurrent;
using System.Numerics;
using DatReaderWriter.DBObjs;
using DatReaderWriter.Enums;
using DatReaderWriter.Types;
using Plane = System.Numerics.Plane;
using UcgEnvCell = AcDream.Core.World.Cells.EnvCell;
using UcgCellGraph = AcDream.Core.World.Cells.CellGraph;

namespace AcDream.Core.Physics;

/// <summary>
/// Thread-safe cache of physics-relevant data extracted from GfxObj and Setup
/// dat objects during streaming. Populated by the streaming worker thread;
/// read by the physics engine on the game/render thread. ConcurrentDictionary
/// makes cross-thread access safe without a global lock.
/// </summary>
public sealed class PhysicsDataCache
{
    private readonly ConcurrentDictionary<uint, GfxObjPhysics> _gfxObj = new();
    private readonly ConcurrentDictionary<uint, GfxObjVisualBounds> _visualBounds = new();
    private readonly ConcurrentDictionary<uint, SetupPhysics> _setup = new();
    private readonly ConcurrentDictionary<uint, CellPhysics> _cellStruct = new();

    // ── Phase 2: building portal cache for outdoor→indoor entry ───────────
    private readonly ConcurrentDictionary<uint, BuildingPhysics> _buildings = new();

    /// <summary>
    /// UCG Stage 1: the unified cell graph, built alongside the legacy cell caches.
    /// Consumed by nobody this stage (zero behavior change).
    /// </summary>
    public UcgCellGraph CellGraph { get; } = new();

    /// <summary>
    /// Extract and cache the physics BSP + polygon data from a GfxObj,
    /// PLUS always cache a visual AABB from the vertex data regardless of
    /// the HasPhysics flag. The visual AABB is used as a collision fallback
    /// for entities whose Setup has no retail physics data — it lets the
    /// user collide with decorative meshes that don't have a CylSphere or
    /// per-part BSP.
    /// </summary>
    public void CacheGfxObj(uint gfxObjId, GfxObj gfxObj)
    {
        // Always cache a visual AABB from the mesh vertices — this is cheap
        // and fed by the mesh data that's already loaded. It serves as the
        // fallback collision shape for pure-visual entities.
        if (!_visualBounds.ContainsKey(gfxObjId) && gfxObj.VertexArray != null)
        {
            _visualBounds[gfxObjId] = ComputeVisualBounds(gfxObj.VertexArray);
        }

        if (_gfxObj.ContainsKey(gfxObjId)) return;
        if (!gfxObj.Flags.HasFlag(GfxObjFlags.HasPhysics)) return;
        if (gfxObj.PhysicsBSP?.Root is null) return;
        if (gfxObj.VertexArray is null) return;

        var physics = new GfxObjPhysics
        {
            BSP = gfxObj.PhysicsBSP,
            PhysicsPolygons = gfxObj.PhysicsPolygons,
            BoundingSphere = gfxObj.PhysicsBSP.Root.BoundingSphere,
            Vertices = gfxObj.VertexArray,
            Resolved = ResolvePolygons(gfxObj.PhysicsPolygons, gfxObj.VertexArray),
        };
        _gfxObj[gfxObjId] = physics;

        if (PhysicsDiagnostics.ProbeDumpGfxObjsEnabled
            && PhysicsDiagnostics.ProbeDumpGfxObjIds.Contains(gfxObjId))
        {
            try
            {
                var dump = GfxObjDumpSerializer.Capture(gfxObjId, physics);
                var path = System.IO.Path.Combine(
                    PhysicsDiagnostics.ProbeDumpGfxObjsPath,
                    System.FormattableString.Invariant($"0x{gfxObjId:X8}.gfxobj.json"));
                GfxObjDumpSerializer.Write(dump, path);
                Console.WriteLine(System.FormattableString.Invariant(
                    $"[gfxobj-dump] wrote 0x{gfxObjId:X8} polys={dump.ResolvedPolygons.Count} → {path}"));
            }
            catch (Exception ex)
            {
                Console.WriteLine(System.FormattableString.Invariant(
                    $"[gfxobj-dump] FAILED to dump 0x{gfxObjId:X8}: {ex.GetType().Name}: {ex.Message}"));
            }
        }
    }

    /// <summary>
    /// Get the cached visual AABB for a GfxObj, or null if not cached.
    /// </summary>
    public GfxObjVisualBounds? GetVisualBounds(uint gfxObjId) =>
        _visualBounds.TryGetValue(gfxObjId, out var vb) ? vb : null;

    /// <summary>
    /// Compute a tight axis-aligned bounding box over all vertices in the mesh.
    /// Used as a fallback collision shape for entities whose Setup has no
    /// physics data — we approximate collision using the visual extent.
    /// </summary>
    private static GfxObjVisualBounds ComputeVisualBounds(VertexArray vertexArray)
    {
        if (vertexArray.Vertices == null || vertexArray.Vertices.Count == 0)
        {
            return new GfxObjVisualBounds
            {
                Min = Vector3.Zero,
                Max = Vector3.Zero,
                Center = Vector3.Zero,
                Radius = 0f,
                HalfExtents = Vector3.Zero,
            };
        }

        var min = new Vector3(float.MaxValue);
        var max = new Vector3(float.MinValue);
        foreach (var kv in vertexArray.Vertices)
        {
            var p = kv.Value.Origin;
            if (p.X < min.X) min.X = p.X;
            if (p.Y < min.Y) min.Y = p.Y;
            if (p.Z < min.Z) min.Z = p.Z;
            if (p.X > max.X) max.X = p.X;
            if (p.Y > max.Y) max.Y = p.Y;
            if (p.Z > max.Z) max.Z = p.Z;
        }

        var center = (min + max) * 0.5f;
        var halfExt = (max - min) * 0.5f;
        float radius = halfExt.Length();

        return new GfxObjVisualBounds
        {
            Min = min,
            Max = max,
            Center = center,
            Radius = radius,
            HalfExtents = halfExt,
        };
    }

    /// <summary>
    /// Extract and cache the collision shape data from a Setup.
    /// No-ops if the id is already cached.
    /// </summary>
    public void CacheSetup(uint setupId, Setup setup)
    {
        if (_setup.ContainsKey(setupId)) return;
        _setup[setupId] = new SetupPhysics
        {
            CylSpheres = setup.CylSpheres ?? new(),
            Spheres = setup.Spheres ?? new(),
            Height = setup.Height,
            Radius = setup.Radius,
            StepUpHeight = setup.StepUpHeight,
            StepDownHeight = setup.StepDownHeight,
        };
    }

    /// <summary>
    /// Extract and cache the physics BSP + polygon data from a CellStruct
    /// (indoor room geometry). No-ops if the id is already cached or the
    /// CellStruct has no physics BSP.
    /// </summary>
    public void CacheCellStruct(uint envCellId, DatReaderWriter.DBObjs.EnvCell envCell,
                                CellStruct cellStruct, Matrix4x4 worldTransform)
    {
        // UCG Stage 1: register in the unified graph for ALL cells — before the
        // idempotency + null-BSP guards below, so BSP-less cells are still included.
        if (!CellGraph.Contains(envCellId))
            CellGraph.Add(UcgEnvCell.FromDat(envCellId, envCell, cellStruct, worldTransform));

        if (_cellStruct.ContainsKey(envCellId)) return;
        if (cellStruct.PhysicsBSP?.Root is null) return;

        Matrix4x4.Invert(worldTransform, out var inverseTransform);

        var resolved = ResolvePolygons(cellStruct.PhysicsPolygons, cellStruct.VertexArray);

        // Visible polygons — portals reference these (NOT PhysicsPolygons).
        var portalPolygons = ResolvePolygons(cellStruct.Polygons, cellStruct.VertexArray);

        // Portal list from envCell.CellPortals.
        var portals = new System.Collections.Generic.List<PortalInfo>(envCell.CellPortals.Count);
        foreach (var p in envCell.CellPortals)
        {
            portals.Add(new PortalInfo(
                otherCellId: p.OtherCellId,
                polygonId:   p.PolygonId,
                flags:       (ushort)p.Flags));
        }

        // VisibleCells set — populated for future use; not consulted this phase.
        // envCell.VisibleCells is List<UInt16> per the DatReaderWriter shape — iterate directly, no .Keys.
        var visibleCellIds = new System.Collections.Generic.HashSet<uint>();
        if (envCell.VisibleCells is not null)
        {
            uint lbPrefix = envCellId & 0xFFFF0000u;
            foreach (var lowId in envCell.VisibleCells)
                visibleCellIds.Add(lbPrefix | lowId);
        }

        var cellPhysics = new CellPhysics
        {
            BSP = cellStruct.PhysicsBSP,
            PhysicsPolygons = cellStruct.PhysicsPolygons,
            Vertices = cellStruct.VertexArray,
            WorldTransform = worldTransform,
            InverseWorldTransform = inverseTransform,
            Resolved = resolved,
            // ── Phase 2 portal fields ──
            CellBSP = cellStruct.CellBSP,
            Portals = portals,
            PortalPolygons = portalPolygons,
            VisibleCellIds = visibleCellIds,
        };
        _cellStruct[envCellId] = cellPhysics;

        if (PhysicsDiagnostics.ProbeDumpCellsEnabled
            && PhysicsDiagnostics.ProbeDumpCellIds.Contains(envCellId))
        {
            try
            {
                var dump = CellDumpSerializer.Capture(envCellId, cellPhysics);
                var path = System.IO.Path.Combine(
                    PhysicsDiagnostics.ProbeDumpCellsPath,
                    System.FormattableString.Invariant($"0x{envCellId:X8}.json"));
                CellDumpSerializer.Write(dump, path);
                Console.WriteLine(System.FormattableString.Invariant(
                    $"[cell-dump] wrote 0x{envCellId:X8} polys={dump.ResolvedPolygons.Count} portals={dump.Portals.Count} → {path}"));
            }
            catch (Exception ex)
            {
                Console.WriteLine(System.FormattableString.Invariant(
                    $"[cell-dump] FAILED to dump 0x{envCellId:X8}: {ex.GetType().Name}: {ex.Message}"));
            }
        }

        if (PhysicsDiagnostics.ProbeCellCacheEnabled)
        {
            var root = cellStruct.PhysicsBSP?.Root;
            int bspRootPolyCount   = root?.Polygons?.Count ?? 0;
            bool bspRootHasChildren = root?.PosNode is not null || root?.NegNode is not null;

            int bspTotalLeafPolys = 0;
            int bspUnmatchedIds   = 0;
            if (root is not null)
            {
                var stack = new System.Collections.Generic.Stack<DatReaderWriter.Types.PhysicsBSPNode>();
                stack.Push(root);
                while (stack.Count > 0)
                {
                    var n = stack.Pop();
                    if (n.Polygons is not null)
                    {
                        foreach (var pid in n.Polygons)
                        {
                            bspTotalLeafPolys++;
                            if (!resolved.ContainsKey(pid)) bspUnmatchedIds++;
                        }
                    }
                    if (n.PosNode is not null) stack.Push(n.PosNode);
                    if (n.NegNode is not null) stack.Push(n.NegNode);
                }
            }

            var bs = root?.BoundingSphere;
            string bsStr = bs is null
                ? "bsphere=n/a"
                : System.FormattableString.Invariant(
                    $"bsphere=({bs.Origin.X:F2},{bs.Origin.Y:F2},{bs.Origin.Z:F2}) r={bs.Radius:F2}");

            var worldOrigin = Vector3.Transform(Vector3.Zero, worldTransform);

            // A6.P3 slice 4 (2026-05-22): also dump portal targets so we
            // can see which cells the player should be able to transition
            // to (issue #98 investigation: cellar-up stuck at top of ramp).
            string portalTargets;
            if (portals.Count == 0)
            {
                portalTargets = "portalTargets=[]";
            }
            else
            {
                var sb = new System.Text.StringBuilder("portalTargets=[");
                for (int i = 0; i < portals.Count; i++)
                {
                    if (i > 0) sb.Append(',');
                    sb.Append(System.FormattableString.Invariant(
                        $"(cell=0x{portals[i].OtherCellId:X4},poly=0x{portals[i].PolygonId:X4},flags=0x{portals[i].Flags:X4})"));
                }
                sb.Append(']');
                portalTargets = sb.ToString();
            }

            Console.WriteLine(System.FormattableString.Invariant(
                $"[cell-cache] envCellId=0x{envCellId:X8} physicsPolyCount={cellStruct.PhysicsPolygons?.Count ?? 0} resolvedCount={resolved.Count} bspTotalLeafPolys={bspTotalLeafPolys} bspUnmatchedIds={bspUnmatchedIds} {bsStr} portalCount={portals.Count} visibleCells={visibleCellIds.Count} cellBspRoot={(cellStruct.CellBSP?.Root is null ? "null" : "ok")} worldOrigin=({worldOrigin.X:F2},{worldOrigin.Y:F2},{worldOrigin.Z:F2}) {portalTargets}"));
        }

        if (PhysicsDiagnostics.ProbeWalkMissEnabled)
        {
            int walkableCount = 0;
            foreach (var entry in WalkMissDiagnostic.EnumerateWalkable(
                         resolved, PhysicsGlobals.FloorZ))
                walkableCount++;

            Console.Write(System.FormattableString.Invariant(
                $"[floor-polys] cellId=0x{envCellId:X8} walkableCount={walkableCount}"));
            foreach (var entry in WalkMissDiagnostic.EnumerateWalkable(
                         resolved, PhysicsGlobals.FloorZ))
            {
                Console.Write(System.FormattableString.Invariant(
                    $" [id=0x{entry.PolyId:X4} nz={entry.NormalZ:F3} bbox=({entry.BboxMin.X:F2},{entry.BboxMin.Y:F2})..({entry.BboxMax.X:F2},{entry.BboxMax.Y:F2}) planeZ@center={entry.PlaneZAtBboxCenter:F3}]"));
            }
            Console.WriteLine();
        }
    }

    /// <summary>
    /// Pre-resolve all physics polygons: lookup vertex positions from VertexArray
    /// and compute the face plane. Matches ACE's Polygon constructor which calls
    /// make_plane() and resolves Vertices from VertexIDs at load time.
    /// </summary>
    internal static Dictionary<ushort, ResolvedPolygon> ResolvePolygons(
        Dictionary<ushort, DatReaderWriter.Types.Polygon> polys,
        VertexArray vertexArray)
    {
        var resolved = new Dictionary<ushort, ResolvedPolygon>(polys.Count);
        foreach (var (id, poly) in polys)
        {
            int numVerts = poly.VertexIds.Count;
            if (numVerts < 3) continue;

            var verts = new Vector3[numVerts];
            bool valid = true;
            for (int i = 0; i < numVerts; i++)
            {
                ushort vid = (ushort)poly.VertexIds[i];
                if (!vertexArray.Vertices.TryGetValue(vid, out var sv))
                { valid = false; break; }
                verts[i] = sv.Origin;
            }
            if (!valid) continue;

            // Compute plane normal using ACE's make_plane algorithm:
            // fan cross-product accumulation + normalization.
            var normal = Vector3.Zero;
            for (int i = 1; i < numVerts - 1; i++)
            {
                var v1 = verts[i] - verts[0];
                var v2 = verts[i + 1] - verts[0];
                normal += Vector3.Cross(v1, v2);
            }
            float len = normal.Length();
            if (len < 1e-8f) continue;
            normal /= len;

            // D = -(average dot(normal, vertex))
            float dotSum = 0f;
            for (int i = 0; i < numVerts; i++)
                dotSum += Vector3.Dot(normal, verts[i]);
            float d = -(dotSum / numVerts);

            resolved[id] = new ResolvedPolygon
            {
                Vertices = verts,
                Plane = new Plane(normal, d),
                NumPoints = numVerts,
                SidesType = poly.SidesType,
                Id = id,
            };
        }
        return resolved;
    }

    public GfxObjPhysics? GetGfxObj(uint id) => _gfxObj.TryGetValue(id, out var p) ? p : null;

    /// <summary>
    /// Issue #101 (2026-05-25): retail-faithful phantom check for
    /// GfxObj-only entity sources. Returns true when the entity's
    /// <c>SourceGfxObjOrSetupId</c> is a GfxObj (high byte
    /// <c>0x01</c>) AND has no cached <see cref="GfxObjPhysics"/> —
    /// meaning the underlying GfxObj had <c>HasPhysics=False</c> or
    /// a null <c>PhysicsBSP.Root</c>, so <see cref="CacheGfxObj"/>
    /// short-circuited at the early-return on line 45/46. Retail's
    /// <c>CPartArray::InitParts</c> emits NO collision shapes for
    /// these — acdream's <c>mesh-aabb-fallback</c> synthesis at
    /// <c>GameWindow.cs:6127</c> must do the same.
    /// </summary>
    public bool IsPhantomGfxObjSource(uint sourceId)
    {
        if ((sourceId & 0xFF000000u) != 0x01000000u) return false;
        return GetGfxObj(sourceId)?.BSP?.Root is null;
    }

    public SetupPhysics? GetSetup(uint id) => _setup.TryGetValue(id, out var p) ? p : null;
    public CellPhysics? GetCellStruct(uint id) => _cellStruct.TryGetValue(id, out var p) ? p : null;
    public int GfxObjCount => _gfxObj.Count;
    public int SetupCount => _setup.Count;
    public int CellStructCount => _cellStruct.Count;

    /// <summary>
    /// Indoor walking Phase 1 (2026-05-19). Snapshot of currently-cached
    /// EnvCell ids — used by <see cref="AcDream.Core.Selection.WorldPicker"/>
    /// to enumerate occluder candidates without exposing the underlying
    /// dictionary. Returns the live key-set; callers should snapshot the
    /// collection if they need stability across frames.
    /// </summary>
    public IReadOnlyCollection<uint> CellStructIds => (IReadOnlyCollection<uint>)_cellStruct.Keys;

    /// <summary>
    /// Register a pre-built <see cref="GfxObjPhysics"/> directly.
    /// Intended for unit-test fixtures that construct synthetic BSP trees
    /// without needing real DAT content.
    /// </summary>
    public void RegisterGfxObjForTest(uint gfxObjId, GfxObjPhysics physics)
        => _gfxObj[gfxObjId] = physics;

    /// <summary>
    /// Register a pre-built <see cref="CellPhysics"/> directly. Intended for
    /// unit-test fixtures that construct synthetic cells without going through
    /// dat-driven <see cref="CacheCellStruct"/>.
    /// </summary>
    public void RegisterCellStructForTest(uint envCellId, CellPhysics physics)
        => _cellStruct[envCellId] = physics;

    /// <summary>
    /// Indoor walking Phase 2 (2026-05-19). Cache the building portal list
    /// for an outdoor landcell that contains a building stab. Used by
    /// <see cref="CellTransit.CheckBuildingTransit"/>.
    /// </summary>
    public void CacheBuilding(uint landcellId, IReadOnlyList<BldPortalInfo> portals, Matrix4x4 worldTransform)
    {
        if (_buildings.ContainsKey(landcellId)) return;
        Matrix4x4.Invert(worldTransform, out var inverse);
        _buildings[landcellId] = new BuildingPhysics
        {
            WorldTransform = worldTransform,
            InverseWorldTransform = inverse,
            Portals = portals,
        };
    }

    public BuildingPhysics? GetBuilding(uint landcellId)
        => _buildings.TryGetValue(landcellId, out var b) ? b : null;

    public IReadOnlyCollection<uint> BuildingIds => (IReadOnlyCollection<uint>)_buildings.Keys;

    /// <summary>Test helper, mirrors <see cref="RegisterCellStructForTest"/>.</summary>
    public void RegisterBuildingForTest(uint landcellId, BuildingPhysics b) => _buildings[landcellId] = b;
}

/// <summary>
/// Visual AABB of a GfxObj mesh — populated for every cached GfxObj regardless
/// of whether it has physics data. Used as a collision fallback shape for
/// entities whose Setup has no CylSpheres/Spheres/Radius (pure decorative
/// meshes). Provides an approximate cylinder matching the visible mesh extent.
/// </summary>
public sealed class GfxObjVisualBounds
{
    /// <summary>Local-space minimum corner of the mesh AABB.</summary>
    public required Vector3 Min { get; init; }
    /// <summary>Local-space maximum corner of the mesh AABB.</summary>
    public required Vector3 Max { get; init; }
    /// <summary>Center of the local-space AABB.</summary>
    public required Vector3 Center { get; init; }
    /// <summary>Local-space radius (diagonal half-length) — loose bound.</summary>
    public required float Radius { get; init; }
    /// <summary>Local-space half-extents ((Max - Min) * 0.5).</summary>
    public required Vector3 HalfExtents { get; init; }
}

/// <summary>
/// A physics polygon with pre-resolved vertex positions and pre-computed plane.
/// ACE pre-computes these in its Polygon constructor; we do it at cache time
/// to avoid per-collision-test vertex lookups.
/// </summary>
public sealed class ResolvedPolygon
{
    public required Vector3[] Vertices { get; init; }
    public required Plane Plane { get; init; }
    public required int NumPoints { get; init; }
    public required CullMode SidesType { get; init; }
    /// <summary>
    /// Polygon index within its parent (cell or GfxObj). Used by the
    /// `ACDREAM_PROBE_POLY_DUMP` probe (A6.P3 slice 4 investigation,
    /// 2026-05-22) to identify which dat polygon a push-back hit so we
    /// can compare our extracted vertices/plane against WorldBuilder's
    /// straight-from-dat read. Defaults to 0 for test fixtures that
    /// don't care about polygon identity.
    /// </summary>
    public ushort Id { get; init; }
}

/// <summary>Cached physics data for a single GfxObj part.</summary>
public sealed class GfxObjPhysics
{
    public required PhysicsBSPTree BSP { get; init; }
    public required Dictionary<ushort, Polygon> PhysicsPolygons { get; init; }
    public Sphere? BoundingSphere { get; init; }
    public required VertexArray Vertices { get; init; }

    /// <summary>
    /// Pre-resolved polygon data with vertex positions and computed planes.
    /// Populated once at cache time so BSP queries don't pay per-test lookup cost.
    /// </summary>
    public required Dictionary<ushort, ResolvedPolygon> Resolved { get; init; }
}

/// <summary>Cached collision shape data for a Setup (character/creature capsule).</summary>
public sealed class SetupPhysics
{
    public List<CylSphere> CylSpheres { get; init; } = new();
    public List<Sphere> Spheres { get; init; } = new();
    public float Height { get; init; }
    public float Radius { get; init; }
    public float StepUpHeight { get; init; }
    public float StepDownHeight { get; init; }
}

/// <summary>
/// Cached physics data for an indoor cell's room geometry (CellStruct).
/// Used for wall/floor/ceiling collision in EnvCells.
/// ACE: EnvCell.find_env_collisions queries CellStructure.PhysicsBSP.
/// </summary>
public sealed class CellPhysics
{
    /// <summary>
    /// The physics BSP tree for this cell. Nullable so that test fixtures
    /// can construct a <see cref="CellPhysics"/> from <see cref="Resolved"/>
    /// alone without needing a real DAT BSP object. Production code must
    /// null-check before traversal: <c>cell.BSP?.Root is not null</c>.
    /// </summary>
    public PhysicsBSPTree? BSP { get; init; }
    public Dictionary<ushort, Polygon>? PhysicsPolygons { get; init; }
    public VertexArray? Vertices { get; init; }
    public Matrix4x4 WorldTransform { get; init; }
    public Matrix4x4 InverseWorldTransform { get; init; }

    /// <summary>
    /// Pre-resolved polygon data with vertex positions and computed planes.
    /// </summary>
    public required Dictionary<ushort, ResolvedPolygon> Resolved { get; init; }

    // ── Indoor walking Phase 2 (2026-05-19): portal-graph fields ───────

    /// <summary>
    /// The cell BSP used for <see cref="BSPQuery.PointInsideCellBsp"/>
    /// (point-in-cell tests). Separate tree from <see cref="BSP"/>
    /// (collision) and from the renderer's drawing-BSP.
    /// Source: <c>cellStruct.CellBSP</c> at cache time.
    /// Nullable: cells without a CellBSP cannot participate in portal
    /// containment and are skipped by <see cref="CellTransit"/>.
    /// </summary>
    public DatReaderWriter.Types.CellBSPTree? CellBSP { get; init; }

    /// <summary>
    /// Portal connections to neighbouring cells, in cell-local space.
    /// Default: empty list. Source: <c>envCell.CellPortals</c>.
    /// </summary>
    public IReadOnlyList<PortalInfo> Portals { get; init; } = System.Array.Empty<PortalInfo>();

    /// <summary>
    /// Resolved VISIBLE polygons (from <c>cellStruct.Polygons</c>),
    /// keyed by polygon id. Distinct from <see cref="Resolved"/> which
    /// holds <c>PhysicsPolygons</c>. Portal lookup via
    /// <see cref="PortalInfo.PolygonId"/> resolves through this dict.
    /// Nullable when the cell has no visible polys (rare).
    /// </summary>
    public Dictionary<ushort, ResolvedPolygon>? PortalPolygons { get; init; }

    /// <summary>
    /// The full cell ids visible from this cell (with landblock prefix).
    /// Populated from <c>envCell.VisibleCells</c> at cache time. Unused
    /// this phase; reserved for the optional <c>find_cell_list</c>
    /// visibility filter.
    /// </summary>
    public IReadOnlySet<uint> VisibleCellIds { get; init; } = new System.Collections.Generic.HashSet<uint>();
}