Replacing a (silently) failing disk in a ZFS pool

Maybe I can’t read, but I have the feeling that official documentations explain every single corner case for a given tool, except the one you will actually need. My today’s struggle: replacing a disk within a FreeBSD ZFS pool. What? there’s a shitton of docs on this topic! Are you stupid? I don’t know, maybe. Yet none covered the process in a simple, straight and complete manner. Here’s the story: