refactor(rendering): prepare retained particle routing

Derive attached particle owners from the exact retained PView route stream with a zero-allocation warm path. Correct G4 gate provenance, record the current production-only RDP sample, and keep G5 old-route deletion explicitly blocked until the reapplied retained cutover passes its connected visual gate.

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

@@ -0,0 +1,120 @@
+namespace AcDream.App.Rendering.Scene;
+
+/// <summary>
+/// Projects the retained PView route stream into particle-owner identities.
+/// This keeps attached-effect routing on the same visibility decision as mesh
+/// submission without walking spatial/gameplay entities a second time.
+/// </summary>
+internal static class RenderFrameRouteOwnerSelector
+{
+    public static void Replace(
+        HashSet<uint> destination,
+        in RenderFrameView view,
+        RenderFrameCandidateRoute route,
+        int routeIndex,
+        uint cellId)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+        destination.Clear();
+        Union(
+            destination,
+            in view,
+            route,
+            routeIndex,
+            cellId);
+    }
+
+    public static void Union(
+        HashSet<uint> destination,
+        in RenderFrameView view,
+        RenderFrameCandidateRoute route,
+        int routeIndex,
+        uint cellId)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+        VisitExact(
+            destination,
+            in view,
+            route,
+            routeIndex,
+            cellId,
+            remove: false);
+    }
+
+    public static void ExceptRoute(
+        HashSet<uint> destination,
+        in RenderFrameView view,
+        RenderFrameCandidateRoute route)
+    {
+        ArgumentNullException.ThrowIfNull(destination);
+
+        ReadOnlySpan<RenderFrameCandidateRange> ranges =
+            view.RouteRanges;
+        ReadOnlySpan<RenderProjectionRecord> candidates =
+            view.RouteCandidates;
+        for (int index = 0; index < ranges.Length; index++)
+        {
+            RenderFrameCandidateRange range = ranges[index];
+            if (range.Route != route)
+                continue;
+
+            ApplyRange(
+                destination,
+                candidates,
+                in range,
+                remove: true);
+        }
+    }
+
+    private static void VisitExact(
+        HashSet<uint> destination,
+        in RenderFrameView view,
+        RenderFrameCandidateRoute route,
+        int routeIndex,
+        uint cellId,
+        bool remove)
+    {
+        ReadOnlySpan<RenderFrameCandidateRange> ranges =
+            view.RouteRanges;
+        ReadOnlySpan<RenderProjectionRecord> candidates =
+            view.RouteCandidates;
+        for (int index = 0; index < ranges.Length; index++)
+        {
+            RenderFrameCandidateRange range = ranges[index];
+            if (range.Route != route
+                || range.RouteIndex != routeIndex
+                || range.CellId != cellId)
+            {
+                continue;
+            }
+
+            ApplyRange(
+                destination,
+                candidates,
+                in range,
+                remove);
+            return;
+        }
+    }
+
+    private static void ApplyRange(
+        HashSet<uint> destination,
+        ReadOnlySpan<RenderProjectionRecord> candidates,
+        in RenderFrameCandidateRange range,
+        bool remove)
+    {
+        ReadOnlySpan<RenderProjectionRecord> owners =
+            candidates.Slice(range.Offset, range.Count);
+        for (int index = 0; index < owners.Length; index++)
+        {
+            uint localEntityId = owners[index].Source.LocalEntityId;
+            if (localEntityId == 0)
+                continue;
+
+            if (remove)
+                destination.Remove(localEntityId);
+            else
+                destination.Add(localEntityId);
+        }
+    }
+}