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.Core.Tests/Meshing/CellStructSideCandidatesTests.cs

@@ -79,11 +79,19 @@ public class CellStructSideCandidatesTests
     [InlineData(3)]
     [InlineData(-1)]
     [InlineData(99)]
-    public void UnknownSidesValue_YieldsNoCandidates(int rawSidesType)
+    public void UnknownSidesValue_FallsBackToRetailSingleSideShape(int rawSidesType)
     {
+        // ConstructMesh @0x0059DFA0 initializes both loop bounds to 1 and
+        // widens them only on an exact 1 / 2 match, so any other raw value
+        // constructs the single positive fan (S1 review finding, 2026-09-02).
         var candidates = CellStructSideCandidates.GetCandidates(rawSidesType);
 
-        Assert.True(candidates.IsEmpty);
+        var single = Assert.Single(candidates.ToArray());
+        Assert.Equal(CellStructPolygonSurfaceSide.Positive, single.SurfaceSlot);
+        Assert.Equal(0, single.CopyOrdinal);
+        Assert.Equal(1, single.NormalSign);
+        Assert.False(single.ReverseWinding);
+        Assert.False(CellStructSideCandidates.IsRetailDefinedSidesType(rawSidesType));
     }
 
     // ---- exact fan index order (§3.4 "Fan index order" column) ----