😄 I just realized this was compiled in "safe" mode – "fast" mode runs even faster.
The safety checks are very useful during development. The sandboxing done by the WebAssembly runtime means that even "fast" code is safe from a security perspective. Still not as safe from a correctness perspective, though, since certain bugs, eg. accessing past the end of an array, would be detected in safe mode but not fast mode.
Good question! I haven't seen a WASM-compiled Zig compiler, but I just checked and my local zig binary is 138.8mb. Not sure how much of that would be necessary for a stripped-down compiler to interactively compile code for development, though I suspect it would be much smaller.