perf(streaming): reserve destination reveal capacity

Join destination scheduling to the canonical reveal generation, protect its share across every typed frame-budget dimension, and prevent stale work from clearing a replacement reservation. Remove forced incomplete materialization and project retail's centered portal wait cue while the authored tunnel remains active.

Tests: Release build clean; 91 focused reservation/reveal tests; full solution 8,158 passed, 5 skipped.

Co-authored-by: Codex <noreply@openai.com>

src/AcDream.App/UI/PortalWaitNoticeController.cs

@@ -0,0 +1,64 @@
+using System.Numerics;
+
+namespace AcDream.App.UI;
+
+/// <summary>
+/// Retained presentation of retail's ECM_UI display-string notice emitted by
+/// <c>gmSmartBoxUI::UseTime @ 0x004D6E30</c> while portal-space cell blocking
+/// continues. It is a centered overlay, not a chat message.
+/// </summary>
+internal sealed class PortalWaitNoticeController : IDisposable
+{
+    private readonly UiRoot _root;
+    private readonly UiText _text;
+    private UiText.Line[] _lines = [];
+    private bool _disposed;
+
+    public PortalWaitNoticeController(UiRoot root)
+    {
+        _root = root ?? throw new ArgumentNullException(nameof(root));
+        _text = new UiText
+        {
+            Name = "PortalSpaceWaitNotice",
+            Left = 0f,
+            Top = 0f,
+            Width = root.Width,
+            Height = root.Height,
+            Anchors = AnchorEdges.Left
+                | AnchorEdges.Top
+                | AnchorEdges.Right
+                | AnchorEdges.Bottom,
+            Centered = true,
+            OneLine = true,
+            ClickThrough = true,
+            ZOrder = int.MaxValue,
+            DefaultColor = Vector4.One,
+            Visible = false,
+        };
+        _text.LinesProvider = () => _lines;
+        _root.AddChild(_text);
+    }
+
+    public void Set(string? message)
+    {
+        ObjectDisposedException.ThrowIf(_disposed, this);
+        if (string.IsNullOrEmpty(message))
+        {
+            _text.Visible = false;
+            _lines = [];
+            return;
+        }
+
+        _lines = [new UiText.Line(message, Vector4.One)];
+        _text.Visible = true;
+    }
+
+    public void Dispose()
+    {
+        if (_disposed)
+            return;
+
+        _root.RemoveChild(_text);
+        _disposed = true;
+    }
+}