Lights up the Phase A WebShell on the C-hard pipeline (vendor/skia-
safe-op + crates/wasm-libc-shim, wired in the previous two commits)
so `cargo build --target wasm32-unknown-unknown --features skia`
followed by `wasm-bindgen --target web` produces a browser-loadable
ES module with 0 env.* imports.
What's added:
- WebBackend (src/backend/mod.rs): impl RenderBackend over a
skia-safe raster N32_PREMUL surface; presents each frame to the
host <canvas> via image_snapshot → read_pixels → ImageData →
put_image_data. end_frame surfaces present errors via
last_present_error / take_present_error so a stale failure does
not leak into a subsequent successful frame
- skia_wasm.rs: thin make_raster_surface helper so swapping in a
GPU GrContext (Phase A round 2) is a self-contained change
- mount(canvas_id) entry: locates the host <canvas>, builds a
WebBackend, paints the Phase A red-rect demo synchronously,
propagates any present error as a JsValue exception
- smoke/step-1b.html: manual smoke harness that mounts the shell
and surfaces a structured diagnostic (with regression-mode
LinkError messaging + rebuild instructions) if loading fails
- extern crate wasm_libc_shim as _; in lib.rs to keep the shim's
no_mangle symbols from being dead-code-eliminated
- .gitignore for wasm-bindgen pkg/ output
Cargo.toml feature wiring:
- default = ["web"] keeps the kickoff §1.2 wasm32-clean compile
guard CI green (stub mount, no skia)
- skia = ["dep:skia-safe", "wasm-libc-shim"] opts into the real
WebBackend + raster paint loop; the shim dep is target-gated
so only wasm32-unknown-unknown actually pulls it in
- wasm-bindgen = "=0.2.117" pinned (last release that compiles
on Rust 1.85; bump alongside the toolchain in a future commit)
Verified end-to-end:
- `cargo build … --features skia --release` green
- `wasm-bindgen --target web` produces ../pkg/*.{js,_bg.wasm}
- WebAssembly.Module.imports() returns 22 imports, all from
./openpencil_shell_web_bg.js; 0 env.* imports
- post `wasm-opt -Oz`: 1542 KiB raw / 599 KiB gzip — within
spec §6 ceiling (≤ 1024 KiB gzip)
- the kickoff §1.2 wasm32-clean compile guard still passes
(`cargo check … --no-default-features --features web`)
Browser-side manual smoke (Phase E) is still TODO; the bundle is
structurally LinkError-free but a human still needs to confirm the
red rect actually paints in Safari / Chrome / Firefox before the
sub-phase can be marked complete.
Step 1b §3.2 P0.5B Run path, sub-phase C-hard.2.
5af1674f6b