Add mesh view to WASM webapp plan

PLAN.md

@@ -11,18 +11,6 @@ The GTK desktop app is being abandoned in favor of a web-first approach.
 - **`<canvas>`** receives pixel data via `putImageData` directly from the Rust renderer
 - Rendering is **on-demand**: triggered by Run and drag events only
 
-## Rust WASM API
-
-```rust
-#[wasm_bindgen] pub fn eval(code: &str) -> EvalResult
-#[wasm_bindgen] pub fn render(width: u32, height: u32) -> Uint8ClampedArray
-#[wasm_bindgen] pub fn rotate(dx: f64, dy: f64)
-#[wasm_bindgen] pub fn pan(dx: f64, dy: f64)
-#[wasm_bindgen] pub fn export_stl() -> Uint8Array
-```
-
-`Uint8ClampedArray` slots directly into `new ImageData(arr, w, h)` → `ctx.putImageData()` with no copy.
-
 ## Crate changes
 
 | Item | Action |
@@ -34,24 +22,71 @@ The GTK desktop app is being abandoned in favor of a web-first approach.
 | `kiss3ddeps/` | Delete (only existed for kiss3d) |
 | `luascad/` | Deleted — folded into `src/luascad.rs` |
 
+## Views
+
+### Ray-march preview (primary)
+- Driven by the existing `Renderer` in `src/render.rs` — writes to `&mut [u8]` pixel buffer
+- WASM exposes `render(width, height) -> Uint8ClampedArray`
+- JS feeds the buffer into a `<canvas>` via `ctx.putImageData(new ImageData(arr, w, h))`
+- Mouse drag on canvas → `rotate(dx, dy)` / `pan(dx, dy)` → re-render
+- Fast feedback during editing; re-triggered on every Run
+
+### Mesh view (secondary, like the current kiss3d window)
+- Driven by `tessellation::ManifoldDualContouring` on the Rust side
+- WASM exposes `tessellate() -> Uint8Array` (binary STL bytes)
+- JS uses **Three.js** `STLLoader` to parse the bytes and display the mesh in a WebGL canvas
+- Three.js `OrbitControls` for rotate/pan/zoom of the mesh
+- Same `Uint8Array` is reused for the "Export STL" download — no duplication
+- Tessellation can be slow; triggered explicitly by a **[Mesh]** button, not on every Run
+
+### UI layout
+
+```
+┌──────────────────────────────────────────────────────────────┐
+│  [Run]  [Mesh]  [Export STL]                    (toolbar)    │
+├─────────────────────────┬────────────────────────────────────┤
+│                         │  [Preview] [Mesh]  ← tab toggle    │
+│  CodeMirror 6           │  ┌──────────────────────────────┐  │
+│  (Lua editor)           │  │  <canvas>                    │  │
+│                         │  │  ray-march OR Three.js mesh  │  │
+│                         │  └──────────────────────────────┘  │
+├─────────────────────────┴────────────────────────────────────┤
+│  output / error log                             (bottom)     │
+└──────────────────────────────────────────────────────────────┘
+```
+
+The right panel switches between the ray-march `<canvas>` and the Three.js `<canvas>` via the tab toggle. Three.js is loaded from npm alongside CodeMirror 6, bundled by esbuild.
+
 ## Frontend layout
 
 ```
 index.html
 main.js          ← wires CM6, canvas drag, buttons → WASM calls
 main.css
 pkg/             ← wasm-pack output (truescad.wasm + JS bindings)
-node_modules/    ← CM6 (dev only, bundled by esbuild)
+node_modules/    ← CM6 + Three.js (dev only, bundled by esbuild)
 ```
 
+## Rust WASM API (updated)
+
+```rust
+#[wasm_bindgen] pub fn eval(code: &str) -> EvalResult
+#[wasm_bindgen] pub fn render(width: u32, height: u32) -> Uint8ClampedArray
+#[wasm_bindgen] pub fn rotate(dx: f64, dy: f64)
+#[wasm_bindgen] pub fn pan(dx: f64, dy: f64)
+#[wasm_bindgen] pub fn tessellate() -> Uint8Array   // binary STL — used for mesh view AND export
+```
+
+`tessellate()` replaces the separate `export_stl()` — same output, dual purpose.
+
 ## Phase order
 
 1. **Strip root crate** — delete GTK files, rewrite `Cargo.toml`
-2. **`wasm-bindgen` API** — implement `src/lib.rs` wrapping `render.rs` + `luascad::eval`
+2. **`wasm-bindgen` API** — implement `src/lib.rs` with `eval`/`render`/`rotate`/`pan`/`tessellate`
 3. **Verify WASM builds** — `wasm-pack build --target web`
-4. **Frontend scaffold** — `index.html` + `main.js` + CodeMirror 6
-5. **Wire JS ↔ WASM** — Run button, drag-to-rotate, STL export download
-6. **GitHub Actions** — `wasm-pack build --release` + deploy `dist/` to `gh-pages`
+4. **Frontend scaffold** — `index.html` + `main.js` + CodeMirror 6 + Three.js via esbuild
+5. **Wire JS ↔ WASM** — Run button, ray-march canvas, Mesh button + Three.js STL view, Export download
+6. **GitHub Actions** — npm install + esbuild bundle + `wasm-pack build --release` + deploy `dist/` to `gh-pages`
 
 ## Status