In the first case, I put the full text in between code markup. In the second case, I put the @ in betwee code markup. In the third case, I put the username in between code markup. In the fourth case, I put both the @ and the username in between separate code markups. Each case yields the same result: it links to my proflle.
For what it’s worth, the code markup does work if you surround the inside text in brackets, although the entire text has to be surrounded by code markup. If only ”Hadger]” is surrounded by code markup, as in the second of the following two cases, the code markup doesn’t work: