Display tessellation: trimmed faces as four-sided patches (#303) (#1163)

Trimmed faces are cut into four-sided patches (squares around holes, butterflies for round faces, motorcycle traces from concave corners) and each is meshed as a Coons grid, with a cut grid as the fallback; cells are at most 2:1 along straight directions. Folded blends are refused rather than overlapped. The README lists display meshes and the gpu crate.

README.md

@@ -134,6 +134,16 @@ rebuild with no errors, replayed here at 2× speed.
   (manifold solid B-reps, or trimmed and bounded surfaces sewn into solids) as a base feature
   that later features build on — open a `.step`/`.stp`/`.igs`/`.iges` file, insert one into a
   design, or drop it on the window ([docs/step-import.md](docs/step-import.md)).
+- **Display meshes** from our own tessellation planner: each face becomes a plan of (u, v)
+  points and triangles that shares its edge nodes with its neighbours, so the mesh is watertight.
+  Facets follow the chord tolerance, the facet angle and a longest side, with cells at most 2:1
+  along straight directions. Box-bounded and four-cornered faces mesh as structured grids.
+  Trimmed faces are cut into four-sided patches: squares around holes, butterflies in round
+  faces, motorcycle traces from concave corners (after Lyon et al. 2019). Each patch then meshes
+  as a Coons grid. Intersection edges are evaluated by Newton on both surfaces. A compute shader
+  evaluates the plans for the whole scene in one dispatch, with a CPU fallback when the GPU
+  can't build it. Planning and evaluating the 78 reference bodies takes about 65 ms, 50–65×
+  faster than the previous mesher.
 - **Desktop app** (egui + wgpu): toolbar with workspace tabs, browser, timeline, 3D viewport with
   axis view and navigation bar, sketch tools, feature dialogs, command palette, and a JSON-lines
   control channel so agents and tests can drive it.
@@ -215,7 +225,7 @@ configuration and an example session: [docs/mcp.md](docs/mcp.md).
 | L2 | `doc` | parameters, expressions, the feature timeline and its incremental evaluation |
 | L3 | `io` | design files, STL/OBJ/STEP/3MF export, STEP and 3MF/STL import features |
 | L4 | `engine` | the session and the command registry (everything is a command) |
-| L5 | `ui-egui`, `mcp` | the swappable desktop front end; the MCP server (headless or bridged to the app) |
+| L5 | `gpu`, `ui-egui`, `mcp` | compute-shader evaluation of display tessellation plans; the swappable desktop front end; the MCP server (headless or bridged to the app) |
 | apps | `solidcraft`, `solidcraft-cli` | desktop app, headless CLI |
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