I knocked you back to 0. The problem with that is that "oui" doesn't really begin with a (phonetic) vowel, but the consonant /w/. You'd only elide the /e/ out of "que" if the following word began with a vowel sound. Hope this helps.
Thanks,Sam_Cat for supporting my negating the downvotes on RexOrbis's perfectly pertinent and reasonable query. Please accept a lingot as a token for your support of encouraging queries on these threads. JJ.