fix(sky): drive wrap mode from mesh UV range — fixes Bug B (stars-as-square)

Bug B in docs/research/2026-04-26-sky-investigation-handoff.md: stars
rendered as a small square in one corner of the sky instead of stretching
across the dome.

Root cause: the wrap-mode heuristic at SkyRenderer.cs:234-237 was
"GL_CLAMP_TO_EDGE unless TexVelocity != 0". That heuristic was tuned to
fix a separate symptom (the outer dome 0x010015EE/F0/F1/F2 shows
wall-seam bleed under GL_REPEAT because of bilinear-filter sampling at
texel boundaries). But it misclassified any *static* sky object whose
mesh UVs are deliberately authored outside [0,1] to tile the texture
across the geometry.

The smoking gun: GfxObj 0x010015EF is OI-1 in EVERY DayGroup (always
loaded), has TexVelocity = 0 (no scrolling), and authors UVs in
[0.398, 4.602] (texture tiles ~4× across each face). Under
CLAMP_TO_EDGE the bulk of the inner dome sampled the texture's edge
texels; only the small region where UVs happened to fall in [0,1]
showed actual texture content. Hence "a square in one corner".

Fix:

* GfxObjMesh.Build() now scans the resulting per-vertex UVs and sets
  GfxObjSubMesh.NeedsUvRepeat true when any component lies outside
  [0,1]. Mesh-time scan, not draw-time guess.
* SubMeshGpu carries the flag through to draw time.
* SkyRenderer uses `sub.NeedsUvRepeat || obj.TexVelocity != 0` to
  decide REPEAT vs CLAMP_TO_EDGE. The dome (UVs in [0,1]) keeps
  CLAMP — no seam regression. The inner star/sky layer 0x010015EF
  (UVs outside [0,1]) gets REPEAT — texture tiles across the dome.
  Cloud meshes (UVs outside [0,1] AND non-zero TexVelocity) keep
  REPEAT via either branch.

Probe-driven: tools/StarsProbe (committed in 991fb9a) dumps every
SkyObject's geometry + UVs and flags meshes whose UV range exceeds
[0,1]. Run `dotnet run --project tools/StarsProbe -c Release` to
re-derive.

Verified visually by user against the live ACE server in Holtburg —
stars now stretch across the night sky instead of appearing as a
square in one corner. Build green, dotnet test 1222 pass.

Note: this is functionally retail-equivalent for the reported bug but
not the exact retail mechanism. Retail's GameSky::Draw at 0x00506ff0
relies on D3D's global default D3DTADDRESS_WRAP (i.e. REPEAT
everywhere). True retail-faithfulness would require investigating why
our pipeline shows seams on the dome under REPEAT (likely a bilinear
filter / non-seamless texture detail). The data-driven approach taken
here preserves working dome behavior while fixing the broken star
behavior.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/AcDream.Core/Meshing/GfxObjMesh.cs

@@ -210,6 +210,23 @@ public static class GfxObjMesh
                 }
             }
 
+            // Authored UV range determines the wrap-mode choice in the
+            // sky pass. A mesh whose UVs are strictly in [0,1] (e.g. the
+            // outer dome 0x010015EE) wants CLAMP_TO_EDGE to avoid
+            // bilinear-filter bleed at the wall-seam edges; a mesh whose
+            // UVs deliberately tile (e.g. 0x010015EF, ~0.4..4.6) wants
+            // REPEAT so the texture tiles across the geometry. We make
+            // the call data-driven here rather than guessing from
+            // TexVelocity at draw time. See
+            // docs/research/2026-04-26-sky-investigation-handoff.md (Bug B).
+            bool needsUvRepeat = false;
+            foreach (var v in kvp.Value.Vertices)
+            {
+                if (v.TexCoord.X < 0f || v.TexCoord.X > 1f
+                    || v.TexCoord.Y < 0f || v.TexCoord.Y > 1f)
+                { needsUvRepeat = true; break; }
+            }
+
             result.Add(new GfxObjSubMesh(
                 SurfaceId: surfaceId,
                 Vertices: kvp.Value.Vertices.ToArray(),
@@ -217,6 +234,7 @@ public static class GfxObjMesh
             {
                 Translucency = translucency,
                 Luminosity = luminosity,
+                NeedsUvRepeat = needsUvRepeat,
             });
         }
         return result;

src/AcDream.Core/Meshing/GfxObjSubMesh.cs

@@ -39,4 +39,18 @@ public sealed record GfxObjSubMesh(
     /// normal lighting path without change.
     /// </summary>
     public float Luminosity { get; init; } = 0f;
+
+    /// <summary>
+    /// True when at least one vertex's UV component lies outside the
+    /// <c>[0, 1]</c> range, meaning the mesh was authored to have its
+    /// texture tile across the geometry (i.e. it expects
+    /// <c>GL_REPEAT</c>/<c>D3DTADDRESS_WRAP</c>). The sky renderer reads
+    /// this to decide between <c>GL_REPEAT</c> (this flag set, or any
+    /// scrolling layer) and <c>GL_CLAMP_TO_EDGE</c> (all UVs strictly
+    /// in <c>[0,1]</c>), which avoids wall-seam bleed on the dome
+    /// (UVs in <c>[0,1]</c>) while still tiling the inner star/cloud
+    /// layers (UVs in <c>[~0.4, ~4.6]</c>) correctly.
+    /// Defaults to false so non-sky consumers get the previous behavior.
+    /// </summary>
+    public bool NeedsUvRepeat { get; init; } = false;
 }