In response to your question at the end of option 2 (How do they know that I've made a copy?) is there any future in either adding a short description above the share buttons that "this is what I might do" OR a twitterbot / mastodonbot / "whatever other network you may get mentions on bot" that mentions them and replies to their share with a "Thanks for sharing your comment - I've added it as a comment to my site".

It doesn't really help if they change their mind much later on, but at least it gives them an opportunity at that moment to ask you to remove it.

That said, if every blog chose to do this, Twitter would become a useless garbage heap of repli....oh. Nevermind.