feat(rendering): journal static scene projections

Append exact static and EnvCell-shell projection deltas only at committed spatial activation and detach receipts. Same-landblock rehydrate now reconciles retained, new, and omitted presentation identities without constructing or drawing the shadow scene in production.

Co-authored-by: Erik Nilsson <erikn@users.noreply.github.com>

src/AcDream.App/Rendering/Scene/RenderProjectionJournal.cs

@@ -0,0 +1,88 @@
+namespace AcDream.App.Rendering.Scene;
+
+/// <summary>
+/// Update-thread-owned structural journal between accepted world mutation and
+/// the disposable render projection. Structural edges are never coalesced.
+/// A successful frame publication drains the complete retained buffer.
+/// </summary>
+internal sealed class RenderProjectionJournal
+{
+    private readonly List<RenderProjectionDelta> _deltas = [];
+    private ulong _nextSequence = 1;
+
+    public RenderProjectionJournal(RenderSceneGeneration generation)
+    {
+        Generation = generation;
+    }
+
+    public RenderSceneGeneration Generation { get; private set; }
+    public int Count => _deltas.Count;
+    public int Capacity => _deltas.Capacity;
+
+    public void Register(in RenderProjectionRecord record) =>
+        _deltas.Add(RenderProjectionDelta.Register(
+            Generation,
+            NextSequence(),
+            in record));
+
+    public void Update(
+        RenderProjectionDeltaKind kind,
+        in RenderProjectionRecord record) =>
+        _deltas.Add(RenderProjectionDelta.Update(
+            kind,
+            Generation,
+            NextSequence(),
+            in record));
+
+    public void Unregister(
+        RenderProjectionId id,
+        RenderOwnerIncarnation incarnation) =>
+        _deltas.Add(RenderProjectionDelta.Unregister(
+            Generation,
+            NextSequence(),
+            id,
+            incarnation));
+
+    public RenderDeltaApplyResult DrainTo(IRenderScene scene)
+    {
+        ArgumentNullException.ThrowIfNull(scene);
+        if (scene.Generation != Generation)
+        {
+            throw new InvalidOperationException(
+                $"Journal {Generation} cannot drain into scene {scene.Generation}.");
+        }
+
+        RenderDeltaApplyResult result =
+            scene.Apply(System.Runtime.InteropServices.CollectionsMarshal.AsSpan(_deltas));
+        _deltas.Clear();
+        return result;
+    }
+
+    public void Clear(RenderSceneGeneration replacementGeneration)
+    {
+        if (replacementGeneration.CompareTo(Generation) <= 0)
+        {
+            throw new ArgumentOutOfRangeException(
+                nameof(replacementGeneration),
+                replacementGeneration,
+                "A replacement journal generation must advance.");
+        }
+
+        _deltas.Clear();
+        Generation = replacementGeneration;
+    }
+
+    internal ReadOnlySpan<RenderProjectionDelta> Pending =>
+        System.Runtime.InteropServices.CollectionsMarshal.AsSpan(_deltas);
+
+    private ulong NextSequence()
+    {
+        if (_nextSequence == ulong.MaxValue)
+        {
+            throw new InvalidOperationException(
+                "Render projection journal sequence exhausted.");
+        }
+
+        return _nextSequence++;
+    }
+}