fix(portal): synchronize destination presentation state

src/AcDream.Core/World/Cells/CellGraph.cs

@@ -63,6 +63,17 @@ public sealed class CellGraph
             if ((id & 0xFFFF0000u) == lb) _envCells.TryRemove(id, out _);
     }
 
+    /// <summary>
+    /// Remove only a landblock's indoor environment cells while preserving its
+    /// outdoor terrain registration. Used by Near-to-Far streaming demotion.
+    /// </summary>
+    public void RemoveEnvCellsForLandblock(uint landblockPrefix)
+    {
+        uint lb = landblockPrefix & 0xFFFF0000u;
+        foreach (var id in new List<uint>(_envCells.Keys))
+            if ((id & 0xFFFF0000u) == lb) _envCells.TryRemove(id, out _);
+    }
+
     /// <summary>The universal id-&gt;cell resolver (retail CObjCell::GetVisible).</summary>
     public ObjCell? GetVisible(uint id)
     {

src/AcDream.Core/World/LandblockLoader.cs

@@ -40,8 +40,8 @@ public static class LandblockLoader
 
         // When landblockId is non-zero, namespace stab Ids globally:
         //   0xC0XXYY00 + n, where XX = lbX byte, YY = lbY byte
-        // matching the scenery (0x80XXYY00) and interior (0x40XXYY00) patterns
-        // in GameWindow.cs. The 0xC0 top byte distinguishes stabs from those.
+        // distinct from the 0x8XXYYIII scenery and 0x4XXYYIII interior
+        // namespaces in GameWindow.cs. The 0xC0 top byte distinguishes stabs.
         //
         // Pre-Tier-1 callers (existing tests) pass landblockId=0 and get the
         // legacy starting-from-1 monotonic Ids — compatible with their assertions

src/AcDream.Core/World/ProceduralSceneryIdAllocator.cs

@@ -0,0 +1,39 @@
+namespace AcDream.Core.World;
+
+/// <summary>
+/// Allocates stable, collision-free ids for procedurally generated scenery.
+///
+/// <para>
+/// The top nibble is fixed at <c>0x8</c>, so bit 31 continues to identify
+/// procedural scenery to every renderer and physics consumer. The remaining
+/// 28 bits are X(8), Y(8), and a 12-bit per-landblock counter:
+/// <c>0x8XXYYIII</c>. No consumer decodes the former byte-aligned
+/// <c>0x80XXYYII</c> layout; they classify only on bit 31.
+/// </para>
+///
+/// <para>
+/// The old 8-bit counter aborted generation after 256 drawable spawns. That
+/// exception rejected the entire streamed landblock before render publication,
+/// exposing the grey clear color as portal space ended. A 12-bit counter gives
+/// 4096 entries while retaining full landblock coordinates. Overflow fails
+/// before it can alias the next landblock.
+/// </para>
+/// </summary>
+public static class ProceduralSceneryIdAllocator
+{
+    public const uint MaxCounter = 0xFFFu;
+
+    public static uint Base(uint landblockX, uint landblockY)
+        => 0x80000000u
+           | ((landblockX & 0xFFu) << 20)
+           | ((landblockY & 0xFFu) << 12);
+
+    public static uint Allocate(uint landblockX, uint landblockY, ref uint counter)
+    {
+        if (counter > MaxCounter)
+            throw new InvalidDataException(
+                $"Landblock ({landblockX & 0xFFu:X2},{landblockY & 0xFFu:X2}) exceeds the 4096-entry procedural scenery id namespace.");
+
+        return Base(landblockX, landblockY) + counter++;
+    }
+}

src/AcDream.Core/World/TeleportAnimSequencer.cs

@@ -99,7 +99,8 @@ public sealed class TeleportAnimSequencer
 
     /// <summary>
     /// Advance the machine by <paramref name="dt"/> seconds.
-    /// <paramref name="worldReady"/> = destination collision landblock is resident.
+    /// <paramref name="worldReady"/> = the complete destination-load barrier is
+    /// satisfied (Near-tier render meshes/textures plus collision residency).
     /// Returns the current snapshot + edge-triggered events fired THIS tick.
     /// </summary>
     public (TeleportAnimSnapshot snapshot, IReadOnlyList<TeleportAnimEvent> events)