This change happens because of the implementation of convertsFrom in IdentityExpr. So now we skip past the parentheses.

I don't really understand what's going on with the whole resolve mechanism - is it just the inverse of getConverted or is there more to it?

That's pretty much it, yes. AST classes can override getResolveStep to not be included in the main AST (i.e., when navigating the parent/child nodes in the AST classes). This is done by autogenerating AST classes lik:

class FooBase {
  Element getBar() {
    exists(Bar bar |
      bar_of_foo(this, bar) and
      result = bar.resolve()
    )
  }
}

where resolve is then the TC of getResolveStep.

Currently, resolve only does something in the case of IdentityExprs (which in particular include parenthesis expressions), ExplicitCasts and ImplicitConversions. For the Expr classes we provide aliases for result = getResolveStep() as convertsFrom(result) (the result became a parameter because we couldn't think of a good name), and getConversion(x) can then be implemented as "whatever expression is the result that converted something from x" (i.e., Expr getConversion() { result.convertsFrom(this) }).

Does that make sense?