When we implement this, we should aim to offer editing on all message lists, including "All messages" (zulip/zulip-mobile#5619). If we successfully keep at least the code cleanly separated from that for composing a new message, as described above, then that should be straightforward.

(Potentially we'll decide that we want the UX for editing to remain similar to that for composing a message after all. In that case the code will probably have significant pieces in common. But the key will just be to have the differences between edit and compose cleanly factored out, rather than the edit logic being jammed in awkwardly as it is in zulip-mobile.)

This now has a design — thanks @terpimost! I've edited the issue description to show the design.

Chat thread on a couple of specific points in the design:
https://chat.zulip.org/#narrow/stream/48-mobile/topic/edit-message.20design/near/1930070

I think this is already ripe to work on, though. Both of those are things that will be easy to change later.

Those points have been resolved now; Vlad edited the Figma design and I edited the description above, and together those have the current design that's ready for implementation.

We've had a few requests for this in beta feedback: https://chat.zulip.org/#narrow/channel/48-mobile/topic/Flutter.20beta.3A.20cannot.20edit.20messages/near/2011951

Hello I want to work on this issue. Please assign this to me.
I have implemented the basic functionality, need to work more on UI part.
Here is the screen recording of the same:

@lakshya1goel Sounds good, thanks. As I mentioned just now at #1314 (comment), let's pause work on post-launch features like this one until after the launch is ready; but we can plan for you to pick up the work from there, if you'd like, when that time comes.

(And as a result we'll leave it "unassigned" in GitHub for now, just because I like to reserve the GitHub "assignment" feature on issues to track what work is actively happening rather than what work is planned for the future.)