⚠️ You only need this when you change the C code. npm run dev and npm run build run an ensure-wasm step that rebuilds the WASM core automatically whenever it's missing or a C source is newer than the last build, so normal app work needs nothing extra. The build output is gitignored, not committed. C changes under core/ take effect on the next dev/build. To force a rebuild now, run npm run ensure-wasm.

• Emscripten SDK, providing emcc: at third_party/emsdk in the main checkout (worktrees share it), or anywhere with $EMSDK pointing at it. The version the repo builds with is pinned in package.json under config.emsdk.
• emcc on PATH. Source the emsdk env in the same shell as the build.

core/wasm-build/build.bat is a thin wrapper around build.mjs (the single source of truth for the source list and emcc flags); it writes straight to apps/web/public/wasm/ (with debug info). ensure-wasm calls it for you, but you can run it directly. Activate the Emscripten env first:

cmd /c "<emsdk>\emsdk_env.bat && cd /d <repo>\core\wasm-build && build.bat"

On success it prints Build successful! and the two output files (zelda3.js, zelda3.wasm); on failure BUILD FAILED with the compiler error. After building, restart npm run dev (or reload the renderer) to pick up the new module.

build.mjs holds the source list and emcc flags once. It is the single source of truth and writes to apps/web/public/wasm/. Everything else just delegates to it, so the build can never drift between platforms:

There is no per-function EXPORTED_FUNCTIONS list. Every Wasm* export is tagged EMSCRIPTEN_KEEPALIVE in its .c file, which both retains and exports the symbol. Nothing has to be kept in sync and no symbol has to be added when you write a new export (see Adding a WASM Function). Forget the KEEPALIVE tag and the function compiles fine but throws at the ccall site at runtime.

• emscripten_main.c is the entry point; the app ships through Electron, not an SDL window.
• core/zelda3/snes/ builds three units: ppu.c (the renderer), dma.c and dsp.c (audio). Those are the chips the decompiled game still writes registers to. There is no CPU emulation, because the game's own processor code is what was decompiled into C, which is the point of the port.
• It's a full recompile of dozens of translation units, so expect it to take a while.
• The repo's build-wasm skill automates this exact flow.