Success!!

Just in case you're not aware, you can use hashtags and "at" other mastodon users as you normally would on mastodon without disrupting the post on the lemmy end.

With one exception ... the lemmy community has to be the first "at"-ed handle in the post, as lemmy intentionally pays attention only to the first to prevent spam posts to all/many communities. After the lemmy community, though, you can "at" other mastodon users, or other groups too such as friendica and/or a.gup.pe groups.

On the hashtags, interestingly, when provide one in your post form mastodon, it comes through on lemmy as a link to a search of that hashtag on your mastodon instance. I'm guessing that's a mastodon thing or maybe an activity pub convention.