Nope. It cannot be assumed at all. Maintainer could just as easily tell Claude to review the hand written code you sent instead of spending any effort on it. Maintainer could sit on the patch for months on end only to swoop in later and rewrite it instead of engaging with you, thereby erasing your contribution and attribution. Maintainer could just ignore you entirely despite the pervasive "patches welcome" attitude.

If there's one thing I learned not to do in open source, it's to assume nonsense like that.