feat(render): Phase 3 (Step A) — outdoor-root seeds full-screen OutsideView

Render unification cutover, Step A (additive, behavior-neutral until Step B). When PortalVisibilityBuilder.Build roots at the synthetic outdoor node, seed OutsideView with the full-screen NDC quad so ClipFrameAssembler yields a full-screen OutsideView slice and DrawInside's DrawLandscapeThroughOutsideView draws terrain/sky/scenery/weather as the node's shell — the same callback that already draws the doorway slice for an interior root looking out.

Keyed on a new explicit LoadedCell.IsOutdoorNode flag (set by OutdoorCellNode.Build), NOT a cell-id heuristic: production EnvCell ids are >= 0x100 but test fixtures use low interior ids, so an id test misfired on 4 existing PortalVisibilityBuilderTests.

Nothing roots at the node until Step B, so this is behavior-neutral. Tests: App 216/0 (2 new UnifiedFloodTests incl. the spec section 10 pure-outdoor regression guard + 2 OutdoorCellNode flag assertions).

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

src/AcDream.App/Rendering/CellVisibility.cs

@@ -104,6 +104,16 @@ public sealed class LoadedCell
     /// grab_visible_cells decomp:311878). The stable anchor for the terrain-draw test.
     /// </summary>
     public bool SeenOutside;
+
+    /// <summary>
+    /// Render unification (2026-06-07): true for the synthetic OUTDOOR cell node built by
+    /// <see cref="OutdoorCellNode.Build"/> — the outdoor world modelled as a flood-graph cell whose
+    /// shell is the landscape. <see cref="PortalVisibilityBuilder.Build"/> seeds OutsideView
+    /// full-screen when the root carries this flag (so terrain/sky/scenery draw as the node's shell).
+    /// An explicit flag, not a cell-id heuristic: interior EnvCell ids are >= 0x100 in production but
+    /// test fixtures use low ids for interior cells, so keying on the id would misfire.
+    /// </summary>
+    public bool IsOutdoorNode;
 }
 
 /// <summary>

src/AcDream.App/Rendering/OutdoorCellNode.cs

@@ -20,6 +20,7 @@ public static class OutdoorCellNode
         {
             CellId = outdoorCellId,
             SeenOutside = true,
+            IsOutdoorNode = true,
             WorldTransform = Matrix4x4.Identity,
             InverseWorldTransform = Matrix4x4.Identity,
         };

src/AcDream.App/Rendering/PortalVisibilityBuilder.cs

@@ -76,6 +76,18 @@ public static class PortalVisibilityBuilder
 
         frame.CellViews[cameraCell.CellId] = CellView.FullScreen();
 
+        // Render unification (outdoor-as-cell, 2026-06-07): when the root IS the synthetic outdoor
+        // node, the landscape is visible FULL-SCREEN, so seed OutsideView with the full-screen NDC
+        // quad. ClipFrameAssembler turns that into a full-screen OutsideView slice, so DrawInside's
+        // DrawLandscapeThroughOutsideView draws terrain/sky/scenery/weather as the node's "shell" —
+        // the very same callback that already draws the doorway slice when an INTERIOR root reaches
+        // outdoors. Keyed on the explicit IsOutdoorNode flag (set by OutdoorCellNode.Build), NOT a
+        // cell-id heuristic: production EnvCell ids are >= 0x100 but test fixtures use low interior
+        // ids, so an id test would misfire. An interior root never sets this flag, so the indoor
+        // exit-portal path (OtherCellId==0xFFFF below) still owns the doorway OutsideView region.
+        if (cameraCell.IsOutdoorNode)
+            frame.OutsideView.Add(new ViewPolygon((Vector2[])FullScreenQuad.Clone()));
+
         // Distance-priority work list (retail PView::cell_todo_list). Cells pop closest-first;
         // each cell carries the camera→nearest-portal-vertex distance that put it on the list
         // (retail keys on InitCell's per-portal min-vertex distance, decomp 432988-433004). The