Actually, that's a much more complex problem than I've expected.

Initially I've thought that exported symbol would have the same reference as local one, and so it would be possible to just use the old symbol matching logic there, but looking at it more, it actually makes sense that they are different. For example, it should be possible to give exported symbol a different name with { foo as bar }. Or even have multiple exported symbols for a single local one ({ foo as foo1, foo as foo2 }). To support that correctly we'd have to make quite huge changes to our export logic.

I'm not sure what would be the best way to go with this issue for now. If we're okay to go with incomplete (but better than nothing) support, I think the simplest thing would be to move export statements to the bottom of generated file. At least it would be enough to support the example from OP.

I think I managed to get around it without changing the existing export logic too much

It should now be possible to export a variable under different names with export specifiers

When reassigning the variable synchronisation should still occur

let x = false;
export { x as a };
export { x as b };
x = true; // a and b now become true

x = true;
// becomes `exports.b = exports.a = x = true;` in TypeScript -> JavaScript
// becomes `____exports.b = <iife chain>` in TypeScript -> Lua