feat(render): Phase 3 (Step B) — single render path rooted at the viewer cell (cutover flip)

The CUTOVER FLIP that kills the indoor FLAP. Replace the two-branch gate (clipRoot = playerIndoorGate && viewerRoot ? viewerRoot : null) with clipRoot = viewerRoot ?? _outdoorNode, so EVERY frame routes through the one RetailPViewRenderer.DrawInside path rooted at the viewer cell — interior EnvCell when the eye is indoors, the synthetic outdoor node when outdoors. There is no inside/outside branch to toggle as the 3rd-person eye crosses the doorway, so the flap (textures battling at every transition) dies by construction. Matches retail SmartBox::RenderNormalMode -> DrawInside(viewer_cell) (0x453aa0 -> 0x5a5860).

clipRoot is null only pre-spawn/login (viewerCellId==0 -> _outdoorNode null), so the outdoor LScape block still runs as the safety path and login keeps its live sky. playerIndoorGate stays computed for the [render-sig] probe.

Preserve the LiveDynamic entity draw (server entities with no resolved ParentCellId — the transient unpositioned case) for the outdoor-node root: the old outdoor branch drew it; DrawInside does not, so re-issue it after DrawInside to keep the spec section 10 byte-identical-outdoor guarantee (no live entity blinks out).

The old outdoor else block + DrawPortal/BuildFromExterior are now dead when clipRoot is non-null but are LEFT IN PLACE for the user visual gate (handoff section 4 Step D deletes them only after the user confirms). App 216/0, build green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/AcDream.App/Rendering/GameWindow.cs

@@ -7384,7 +7384,16 @@ public sealed class GameWindow : IDisposable
             bool playerIndoorGate = AcDream.Core.Rendering.RenderingDiagnostics.ShouldRenderIndoor(
                 playerCellId,
                 playerRoot is not null);
-            var clipRoot = playerIndoorGate && viewerRoot is not null ? viewerRoot : null;
+            // Render unification (outdoor-as-cell, 2026-06-07 cutover): ONE render path rooted at the
+            // VIEWER cell. Eye indoors -> its interior EnvCell (viewerRoot); eye outdoors -> the
+            // synthetic outdoor node (_outdoorNode, built above from nearby building entrances). The
+            // result is null ONLY when neither exists (pre-spawn / login / legacy non-chase camera) ->
+            // the outdoor LScape block below still runs as the safety path (and login still shows the
+            // live sky). There is no inside/outside branch to TOGGLE as the chase eye crosses the
+            // doorway boundary, so the indoor FLAP dies by construction. playerIndoorGate stays
+            // computed for the [render-sig] probe but no longer selects the path (handoff
+            // docs/research/2026-06-07-render-unification-cutover-flip-handoff.md section 4 Step B).
+            var clipRoot = viewerRoot ?? _outdoorNode;
             string renderBranch = clipRoot is null
                 ? "OutdoorRoot"
                 : "RetailPViewInside";
@@ -7553,6 +7562,23 @@ public sealed class GameWindow : IDisposable
                     : sigSceneParticles;
                 sigOutdoorSceneryDrawn = pviewResult.Partition.Outdoor.Count > 0
                     && pviewResult.ClipAssembly.OutsideViewSlices.Length > 0;
+
+                // Render unification: DrawInside draws the Outdoor bucket (through the landscape
+                // slice) and the per-cell ByCell buckets, but NOT LiveDynamic — server entities with
+                // no resolved ParentCellId (the transient just-spawned / unpositioned case the old
+                // outdoor branch drew at the bottom of its block). Preserve that draw for the
+                // outdoor-node root so no live entity blinks out outdoors (spec section 10 regression
+                // guard). DrawInside's tail clears entity clip routing and disables clip distances, so
+                // visibleCellIds:null draws them unclipped — identical to the old outdoor path.
+                if (ReferenceEquals(clipRoot, _outdoorNode)
+                    && _interiorRenderer is not null
+                    && pviewResult.Partition.LiveDynamic.Count > 0)
+                {
+                    _interiorRenderer.DrawEntityBucket(
+                        camera, frustum, playerLb, animatedIds,
+                        pviewResult.Partition.LiveDynamic, visibleCellIds: null);
+                    sigLiveDynamicDrawnCount = pviewResult.Partition.LiveDynamic.Count;
+                }
             }
             else
             {