What's unreplied?
I've tweaked who sees a discussion as "unreplied" to improve workflows and ensure a discussion is always red for someone:
If a discussion was initiated by somebody other than the PR author, and there's only one active participant, then the PR author will always see it as unreplied until they or somebody else join the discussion. This is so even if the PR author has acknowledged the discussion.
If a discussion is unresolved with at least two active participants, and everybody has acknowledged the last comment, then all participants who are blocking resolution will see the discussion as unreplied.
Let me know if you run into any corner cases I failed to consider!