It's still not ambiguous. Your second example would be a syntax error (probably, if I was designing it at least) because you're missing the invocation parenthesis after the wrapped value:

    a |> (await f())()

which removes any sort of ambiguity. Your first example calls f() with a as its first argument while the second (after my fix) calls and awaits f() and then invokes that result with a as its first argument.

For the last example, it would look like:

    a |> (await f())() | g()

assuming f() is still async and returns a function. g() must be a function, so the parenthesis have to be added.