Post History

**How should we handle possibly-outdated reactions?**  No, not by reactions to reactions.

An edit to a post made after reactions were added could change the applicability of those reactions.  Somebody might have edited to address a danger or update an out-of-date recommendation.  Conversely, somebody might change an answer that worked for someone in a way that makes it not work any more.  Or, sometimes what worked for somebody leaving a reaction in 2020 might be outdated and not what the person would do, let alone endorse, in 2022.

All of this is true of votes too; a post can have residual votes that those people wouldn't cast *today*.  But votes aren't public.  Reactions are, so I think we owe it to people leaving them to handle obsolescence *somehow*.

Here are some ideas that occurred to me.  We shouldn't do all of them; these are options.  None is a complete solution to the issues I've raised:

- Where we show the names of people who left reactions, also show timestamps, or maybe just the latest timestamp if that's noisy.

- When we show reactions, indicate that the post was edited after they were left.

- In the post history, show the reactions that were present pre-edit.

- Don't show pre-edit reactions immediately, but make them available behind an "older reactions" link.  (Can be defeated by a trivial edit.  Do we need the idea of a substantial edit?  How would we tell?)

- Make it possible to retract reactions.  (We should do that anyway.  We let people delete comments and retract votes, after all.)  This is like the case where you come across a post you had downvoted and then it was edited but you didn't notice, so now that you've seen it again you retract your vote.

- Notify people that posts they reacted to have been edited.  (Could get noisy; might need a user setting to opt out.)