I would suggest lengthening the amount of time a person can edit their post-- even allowing it to “forever” so a user can create an update in their top level post saying it is solved or share a link to whatever solved their original questions.
The settings are under admin/settings if this seems like a good change.
It may be (buried in the forum config settings) that to edit you need to meet [qualifying criteria†]. No spare time to go spelunking right now but i’ll bear this in mind.
† Time since registration, time since post, number of posts, etc.
I’ve seen that “you don’t have permission…” message when I have tried to delete the first note in a thread I started, after other readers have replied to the thread. So, in that case it’s a safety that the thread-originator doesn’t lead the thread headless, I suppose.
It may also be a considered setting by the Discourse devs against the drive-by spam of joining, posting a harmless thing then returning on a second pass to add lots of spam. Of course, this bites the honest members of the forum too. On more thing for my forum to-do list!
Yesterday, the pencil was gone on all of my posts. It is back today. Maybe it was a weird quirk or user error. I use Discourse a lot on several sites and I’ve never encountered that. Oh well, all good now.