perf(vfx): port retail particle visibility degradation

Resolve DAT-authored particle ranges from the hardware GfxObj, apply retail distance and completed-cell visibility gates, and preserve the exact finite/infinite off-view update semantics. This removes dense-world simulation work without shortening terrain, entity, fog, or streaming distance.

Publish doorway-clipped outdoor cells through a focused frame controller, retain effect cell identity for outdoor statics, reject hidden emitters before particle-slot scans, and offer an explicit opt-in Extended particle range.

Release build succeeds and all 5,857 tests pass with five intentional skips. Retail-conformance, architecture, and adversarial review cycles are clean; connected Aerlinthe visual/performance gate pending.

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

src/AcDream.App/Rendering/Vfx/ParticleVisibilityController.cs

@@ -0,0 +1,93 @@
+using System.Numerics;
+using AcDream.Core.Vfx;
+
+namespace AcDream.App.Rendering.Vfx;
+
+/// <summary>
+/// Bridges the retained retail PView result into the next physics update's
+/// <c>CObjCell::IsInView</c> particle gate. The controller owns only immutable
+/// frame meaning: one completed viewer position plus the AC cells admitted by
+/// that completed view. It neither creates emitters nor performs rendering.
+/// </summary>
+public sealed class ParticleVisibilityController
+{
+    public const float ExtendedRangeMultiplier = 2f;
+
+    private readonly HashSet<uint> _buildingCellIds = new();
+    private readonly HashSet<uint> _completedCellIds = new();
+    private Vector3 _buildingViewerPosition;
+    private Vector3 _completedViewerPosition;
+    private bool _frameOpen;
+    private bool _frameUsesWorldView;
+    private bool _hasCompletedWorldView;
+
+    public void BeginFrame(Vector3 viewerPosition)
+    {
+        _buildingCellIds.Clear();
+        _buildingViewerPosition = viewerPosition;
+        _frameUsesWorldView = false;
+        _frameOpen = true;
+    }
+
+    /// <summary>
+    /// Declares that this frame has an authoritative world-visibility product.
+    /// That product can come from the unified retail PView or from the outdoor
+    /// landscape fallback. Login and portal-space frames deliberately omit it;
+    /// dedicated pass and examination emitters carry explicit bypass policies.
+    /// </summary>
+    public void UseWorldView()
+    {
+        if (_frameOpen)
+            _frameUsesWorldView = true;
+    }
+
+    public void MarkVisibleCells(HashSet<uint> cellIds)
+    {
+        ArgumentNullException.ThrowIfNull(cellIds);
+        if (!_frameOpen || !_frameUsesWorldView)
+            return;
+
+        _buildingCellIds.UnionWith(cellIds);
+    }
+
+    public void CompleteFrame()
+    {
+        if (!_frameOpen)
+            return;
+
+        _frameOpen = false;
+        if (!_frameUsesWorldView)
+        {
+            _completedCellIds.Clear();
+            _completedViewerPosition = _buildingViewerPosition;
+            _hasCompletedWorldView = false;
+            return;
+        }
+
+        _completedCellIds.Clear();
+        _completedCellIds.UnionWith(_buildingCellIds);
+        _completedViewerPosition = _buildingViewerPosition;
+        _hasCompletedWorldView = true;
+    }
+
+    public void Apply(ParticleSystem particles, float rangeMultiplier)
+    {
+        ArgumentNullException.ThrowIfNull(particles);
+        particles.ApplyRetailView(
+            _completedViewerPosition,
+            _completedCellIds,
+            _hasCompletedWorldView,
+            rangeMultiplier);
+    }
+
+    public void Reset()
+    {
+        _buildingCellIds.Clear();
+        _completedCellIds.Clear();
+        _frameOpen = false;
+        _frameUsesWorldView = false;
+        _hasCompletedWorldView = false;
+        _buildingViewerPosition = default;
+        _completedViewerPosition = default;
+    }
+}