fix(content): S1 review round - retail default sides shape, mask hoist, upload order

Campaign OVERHAUL S1 review fixes (two Opus lens reviews, findings verified
by the lead against the decomp):

- a raw sides_type outside 0/1/2 constructs retail's default single-side
  shape (ConstructMesh @0x0059DFA0 loop bounds default to 1) instead of
  dropping the polygon; still counted as a data anomaly (corpus has none);
- the positive-surface stippling mask OR runs once per polygon before the
  degenerate-fan guard, as retail's count loop does (pseudo-C 426859-426866);
- untextured slots keep their mask accounting but bake no texture and no
  vertices (contract §9 item 3); the dev pak shrinks by 114 KB;
- failed surface-override / Surface / texture-dependency lookups are
  attempted and logged once per slot, not once per candidate;
- cell-shell batches upload in ascending source surface index, retail's
  built-EnvCell subset draw order (ConstructMesh attribute-range scan,
  DrawMesh @0x0059D4A0); ordinary GfxObj meshes keep storage order;
- CellMesh.HasDrawableGeometry documented as the admission rule without
  texture-dependency resolution (a conservative superset of emission);
- the stippling/surface equivalence sweep's cell half is pinned at zero
  again; InAscendingSurfaceOrder is marked bake/upload/test-only;
- plan §5: reviewer findings are verified by the lead, one skeptic at most
  for a blocking finding, never more than five agents per step.

Three new Content tests pin the mask hoist, the vertex-free untextured
slot, and the single-side fallback. Content 213/213, Core Meshing and
Conformance green, App hermetic 6,757/6,757, Release build 0/0.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

tests/AcDream.Content.Tests/MeshExtractorSolidFaceExtractionTests.cs

@@ -497,6 +497,91 @@ public sealed class MeshExtractorSolidFaceExtractionTests
         Assert.All(mesh.Vertices, vertex => Assert.Equal(Vector2.Zero, vertex.UV));
     }
 
+    [Fact]
+    public void PrepareCellStructMeshData_DegeneratePolygon_StillOrsPositiveSurfaceMask()
+    {
+        // ConstructMesh @0x0059DFA0 count loop (pseudo-C 426859-426866): the
+        // positive-surface stippling OR runs once per polygon BEFORE the
+        // num_pts branch, so a two-vertex polygon that builds no fan still
+        // stamps bit 1 on its positive slot. Slot 0 gets its geometry from
+        // the textured quad (stippling 0, so no bit from it) and its mask bit
+        // only from the degenerate polygon.
+        var dats = new FakeMeshExtractorDats();
+        RegisterCellTexturedSurface(dats);
+        var cellStruct = BuildQuadCellStruct(RetailCullMode.Landblock);
+        cellStruct.Polygons[1] = new Polygon
+        {
+            SidesType = RetailCullMode.Landblock,
+            Stippling = StipplingType.NoPos,
+            PosSurface = 0,
+            NegSurface = -1,
+            VertexIds = [0, 1],
+        };
+        var extractor = new MeshExtractor(dats, NullLogger.Instance, sideStagedSink: null);
+
+        ObjectMeshData mesh = Assert.IsType<ObjectMeshData>(
+            extractor.PrepareCellStructMeshData(
+                id: 1, cellStruct, surfaceOverrides: [2], Matrix4x4.Identity, CancellationToken.None));
+
+        TextureBatchData batch = Assert.Single(Assert.Single(mesh.TextureBatches).Value);
+        Assert.Equal(6, batch.Indices.Count);
+        Assert.Equal(1, batch.RetailSurfaceMask);
+    }
+
+    [Fact]
+    public void PrepareCellStructMeshData_UntexturedSlot_EmitsNoVertices()
+    {
+        // An untextured slot fails built-EnvCell admission (contract §4).
+        // Retail constructs its geometry and never draws it; the prepared
+        // package does not carry vertices that can never draw (contract §9
+        // item 3). Slot 0 is textured, slot 1 is Base1Solid: only the four
+        // vertices of the textured quad may reach the output.
+        var dats = new FakeMeshExtractorDats();
+        RegisterCellTexturedSurface(dats);
+        dats.Register(SolidSurfaceId, new Surface
+        {
+            Type = SurfaceType.Base1Solid,
+            ColorValue = new ColorARGB { Alpha = 255, Red = 64, Green = 96, Blue = 128 },
+        });
+        var cellStruct = BuildQuadCellStruct(RetailCullMode.Landblock);
+        cellStruct.Polygons[1] = new Polygon
+        {
+            SidesType = RetailCullMode.Landblock,
+            PosSurface = 1,
+            NegSurface = -1,
+            VertexIds = [0, 1, 2, 3],
+        };
+        var extractor = new MeshExtractor(dats, NullLogger.Instance, sideStagedSink: null);
+
+        ObjectMeshData mesh = Assert.IsType<ObjectMeshData>(
+            extractor.PrepareCellStructMeshData(
+                id: 1, cellStruct, surfaceOverrides: [2, 1], Matrix4x4.Identity, CancellationToken.None));
+
+        TextureBatchData batch = Assert.Single(Assert.Single(mesh.TextureBatches).Value);
+        Assert.Equal(0, batch.SourceSurfaceIndex);
+        Assert.Equal(4, mesh.Vertices.Length);
+    }
+
+    [Fact]
+    public void PrepareCellStructMeshData_SidesValueOutsideRetailSet_ConstructsSingleSideFan()
+    {
+        // ConstructMesh @0x0059DFA0 initializes both loop bounds to 1 and
+        // widens them only on an exact 1 / 2, so an anomalous raw value
+        // draws as ST_SINGLE rather than vanishing (S1 review finding).
+        var dats = new FakeMeshExtractorDats();
+        RegisterCellTexturedSurface(dats);
+        var cellStruct = BuildQuadCellStruct((RetailCullMode)7);
+        var extractor = new MeshExtractor(dats, NullLogger.Instance, sideStagedSink: null);
+
+        ObjectMeshData mesh = Assert.IsType<ObjectMeshData>(
+            extractor.PrepareCellStructMeshData(
+                id: 1, cellStruct, surfaceOverrides: [2], Matrix4x4.Identity, CancellationToken.None));
+
+        TextureBatchData batch = Assert.Single(Assert.Single(mesh.TextureBatches).Value);
+        Assert.Equal(6, batch.Indices.Count);
+        Assert.Equal(4, mesh.Vertices.Length);
+    }
+
     [Fact]
     public void PrepareCellStructMeshData_TwoSlotsSameSurfaceDid_RemainTwoDistinctSubsets()
     {