What subtleties am I missing that makes "ahead-of-time JS engine" a better description than "JS-to-Wasm compiler"? (If it's mostly a framing strategy, that's cool too.)
There are already projects that does JS-to-WASM by bundling a JS interpreter. So, it's likely to make the difference to those clearer.
Yep! Also as it is technically more of an engine/runtime (sometimes) than "just" a compiler, folks in the JS space are more familiar with engine as a term :)