Great job! 32-to-64-bit conversions are always fun :) One question though. If this is intended for desktop, why bother with WASM at all? Do you gain anything other than less performance?
Is it less performance if you compare the hardware it was probably running on vs today?
Because the same module runs in three places: inside the Electron IDE, in the shipped app, and in the test suite under jsdom, with no native build per platform. The other reason is the boundary itself: wasm exports can't re-enter, which forced the design where every side effect is yielded to the host and the VM is never on the stack while a dialog is up. That's what makes MESSAGEBOX not freeze the window. Perf isn't where these apps hurt, they're I/O and UI bound, and VFP itself was a p-code interpreter. The crate is plain Rust, the CLI runner is native, so a native build is a cargo flag away if it ever matters
Funny enough the customer is one of my dads friends that has been running the same shop for 20 years, wanted bigger tables and keep milking that for the foreseable future. I wanted something simple, no jit stuff, no gc complexity. Just a stack based interpreter. Yes it was LLM assisted like most stuff nowadays.