A robust story (product backlog item; issue) can include a long conversation. If there is a critical comment that doesn't belong in the definition of a story (e.g., Use/consult this sandboxed code/experiment), it would be incredibly useful to highlight it as important.

I suppose by suggesting pinning the comment, I'm specifying a solution. The real need is to highlight a comment as important. I think pinning comments would be a reasonable solution though. Thanks.