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>

tests/AcDream.App.Tests/Rendering/OutdoorCellNodeTests.cs

@@ -33,6 +33,7 @@ public class OutdoorCellNodeTests
 
         Assert.Equal(outdoorId, node.CellId);
         Assert.True(node.SeenOutside);
+        Assert.True(node.IsOutdoorNode); // the flag PortalVisibilityBuilder keys the full-screen OutsideView on
         Assert.Equal(Matrix4x4.Identity, node.WorldTransform);
         Assert.Single(node.Portals);
         Assert.Equal((ushort)(0xA9B40170 & 0xFFFF), node.Portals[0].OtherCellId);
@@ -48,5 +49,6 @@ public class OutdoorCellNodeTests
         var node = OutdoorCellNode.Build(0xA9B40031, System.Array.Empty<LoadedCell>());
         Assert.Empty(node.Portals);
         Assert.True(node.SeenOutside);
+        Assert.True(node.IsOutdoorNode);
     }
 }

tests/AcDream.App.Tests/Rendering/UnifiedFloodTests.cs

@@ -60,4 +60,50 @@ public class UnifiedFloodTests
         var frame = PortalVisibilityBuilder.Build(node, eye, Lookup, view * proj);
         Assert.True(frame.OrderedVisibleCells.Count < 10); // bounded, no runaway
     }
+
+    // Step A (cutover): rooting at the outdoor node must seed OutsideView with the FULL-SCREEN NDC
+    // quad so DrawLandscapeThroughOutsideView draws the landscape as the node's shell. Without this
+    // the outdoor-root frame would have OutsideViewSlices.Length==0 -> TerrainMode.Skip -> no terrain.
+    [Fact]
+    public void Build_RootedAtOutdoorNode_SeedsFullScreenOutsideView()
+    {
+        var building = MakeBuildingCell(0xA9B40170);
+        var node = OutdoorCellNode.Build(0xA9B40031, new[] { building });
+        LoadedCell? Lookup(uint id) => (id & 0xFFFFu) == 0x0170 ? building : null;
+
+        var eye = new Vector3(0, -3, 1);
+        var view = Matrix4x4.CreateLookAt(eye, new Vector3(0, 5, 1), Vector3.UnitZ);
+        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 16f / 9f, 1f, 5000f);
+
+        var frame = PortalVisibilityBuilder.Build(node, eye, Lookup, view * proj);
+
+        Assert.False(frame.OutsideView.IsEmpty);
+        // The union bounds of OutsideView must cover the whole NDC viewport (a full-screen quad),
+        // so ClipFrameAssembler yields TerrainMode != Skip and the terrain draws everywhere.
+        Assert.Equal(-1f, frame.OutsideView.MinX, 3);
+        Assert.Equal(-1f, frame.OutsideView.MinY, 3);
+        Assert.Equal(1f, frame.OutsideView.MaxX, 3);
+        Assert.Equal(1f, frame.OutsideView.MaxY, 3);
+    }
+
+    // Pure-outdoor regression guard (spec section 10): an outdoor node with NO nearby buildings must
+    // resolve to exactly {node} with a full-screen OutsideView -> full-screen terrain, no interior
+    // cells, byte-for-byte today's open-world draw. Visual-gate the open field, not just the cottage.
+    [Fact]
+    public void Build_EmptyOutdoorNode_FullScreenOutsideView_OnlyNodeVisible()
+    {
+        var node = OutdoorCellNode.Build(0xA9B40031, Array.Empty<LoadedCell>());
+        Assert.Empty(node.Portals); // no doorways
+
+        var eye = new Vector3(0, -3, 1);
+        var view = Matrix4x4.CreateLookAt(eye, new Vector3(0, 5, 1), Vector3.UnitZ);
+        var proj = Matrix4x4.CreatePerspectiveFieldOfView(MathF.PI / 3f, 16f / 9f, 1f, 5000f);
+
+        var frame = PortalVisibilityBuilder.Build(node, eye, _ => null, view * proj);
+
+        Assert.Equal(new[] { 0xA9B40031u }, frame.OrderedVisibleCells); // only the node
+        Assert.False(frame.OutsideView.IsEmpty);
+        Assert.Equal(-1f, frame.OutsideView.MinX, 3);
+        Assert.Equal(1f, frame.OutsideView.MaxX, 3);
+    }
 }