Optimize parsed meshes and renderer follow-ups (#58)

* feat(core): optimize parsed meshes by default

* refactor(website): use core mesh optimization

* chore(bench): add gltf simplifier corpus benchmark

* perf(core): speed up parse mesh optimization

* fix(renderer): move corner-shape triangle paint to base CSS

* fix(polycss): share mesh hit testing

* bench(renderer): add rect-cover optimizer variants

---------

Co-authored-by: agustin-littlehat <minotopo@gmail.com>

Author: alowpoly

AGENTS.md

@@ -35,7 +35,7 @@ Voxel-shaped meshes are the exception to "all polygons stay mounted": meshes wit
 | `<b>` | **Quads** | Axis-aligned rectangle, or untextured convex quad when the homography passes stability guards on non-Safari engines | `background: currentColor` on a fixed 64px rectangle; affine and projective quads normalize their `matrix3d` to that primitive, with tiny solid bleed on projective quads to overlap antialias seams. Safari-family browsers skip the projective quad path and fall through because transformed projective rectangles composite incorrectly there. | None |
 | `<i>` | **Border-shape clipped solid** | Untextured non-rect not caught by the exact corner-shape solid path, on browsers with CSS `border-shape` (Chromium + `pointer:fine` + `hover:hover`) | `border-color: currentColor` on a fixed 16px border-shape primitive, clipped by `border-shape: polygon(...)`; polygon bbox scale and tiny solid bleed are folded into `matrix3d` | None |
 | `<s>` | **Atlas slice** | Textured polygons, or untextured non-rect on browsers without `border-shape` | `background-image` slice of packed bitmap on an auto-budgeted fixed primitive (128px for desktop-class `textureQuality="auto"`, 64px for mobile-class `auto` and explicit numeric quality); atlas position/size and `matrix3d` scale are normalized to the slice, shared textured edges get low-alpha atlas pixels repaired during atlas generation, and solid fallbacks get same-color edge bleed to avoid dark alpha fringes | Bounding-rect area |
-| `<u>` | **Stable solid triangle / corner-shape solid** | Triangles on non-WebKit engines; or untextured non-triangle polygons whose normalized outline is exactly a rectangle with one or more beveled corners on browsers with CSS `corner-shape` | Triangles use a 32px box with two beveled top corners and `background: currentColor` when CSS `corner-shape` support is present, progressively falling back to the CSS border-color triangle trick. Firefox uses a 96px border-triangle primitive to avoid large-perspective compositor banding. Exact corner-shape solids use a bare fixed 32px box with inline per-corner radii + `corner-*-shape: bevel` and `background: currentColor`. Tiny solid bleed is folded into `matrix3d`. WebKit/Safari falls through to `<s>` for border triangles because transformed CSS border triangles composite incorrectly there. | None |
+| `<u>` | **Stable solid triangle / corner-shape solid** | Triangles on non-WebKit engines; or untextured non-triangle polygons whose normalized outline is exactly a rectangle with one or more beveled corners on browsers with CSS `corner-shape` | Triangles use a 32px box with two beveled top corners and `background: currentColor` when CSS `corner-shape` support is present, progressively falling back to the CSS border-color triangle trick. Firefox uses a 96px border-triangle primitive to avoid large-perspective compositor banding. Exact corner-shape solids use a fixed 16px classed box with inline per-corner radii + `corner-*-shape: bevel` and `background: currentColor`. Tiny solid bleed is folded into `matrix3d`. WebKit/Safari falls through to `<s>` for border triangles because transformed CSS border triangles composite incorrectly there. | None |
 
 Strategies are ordered cheapest → most expensive. The mesher's job is to maximise `<b>` / `<u>` / `<i>` and minimise `<s>` (see "Meshing implications" below).
 
@@ -55,7 +55,7 @@ All solid/atlas tags work in both modes. The `.vox` direct-matrix fast path is b
 ### Meshing implications (what generators must respect)
 
 - **Polygon count is the dominant cost.** Each polygon is one DOM node, one `matrix3d`, one paint. Halving the polygon count is almost always worth a more complex mesher.
-- **Lossy optimization favors low DOM render cost.** The default `"lossy"` path scores exact and approximate merge candidates by estimated render cost and keeps the cheapest direct candidate. It can also try a more aggressive triangle-pair merge candidate inside the same boundary displacement budget, but accepts it only when the render-cost win is material and whole-mesh seam diagnostics do not get worse. It avoids per-candidate seam-repair passes in the import path; targeted seam repair remains a lower-level helper for explicit repair workflows.
+- **Lossy optimization favors low DOM render cost.** The default `"lossy"` `loadMesh` / core import path first bakes solid texture swatches, merges visually redundant baked swatch colors, and tries endpoint-preserving static triangle simplification for eligible non-animated meshes. It then scores exact and approximate merge candidates by estimated render cost and keeps the cheapest direct candidate. Static simplification has a relaxed seam-key pass plus a stricter source-vertex fallback, and is accepted only when the final optimized DOM leaf count is lower than the baseline optimizer result. The polygon optimizer can also try a more aggressive triangle-pair merge candidate inside the same boundary displacement budget, but accepts it only when the render-cost win is material and whole-mesh seam diagnostics do not get worse. It avoids per-candidate seam-repair passes in the import path; targeted seam repair remains a lower-level helper for explicit repair workflows.
 - **Fill ratio matters.** A textured polygon's atlas slice equals its local-2D bounding rect. Empty space inside that slice is wasted bitmap pixels. Prefer shapes with high `area / boundingRect.area`:
   - axis-aligned rectangle = 1.0 (and hits the fastest path)
   - right-isosceles triangle = 0.5