fix(drafts): preserve reply drafts across forum moves

docs/members/member-guide.md

@@ -17,7 +17,8 @@ Open a forum or use **New posts**, **Unanswered**, **My posts** or **Search**. S
 3. Add permitted attachments or a poll.
 4. Submit. Posts held for approval appear after moderator review.
 
-See [Formatting](formatting.md) for Markdown. Resume saved drafts at `/usercp/drafts`. Editing and deletion may have permission or time limits.
+See [Formatting](formatting.md) for Markdown. Resume saved drafts at `/usercp/drafts`. Reply drafts follow a thread when it moves
+to another forum, provided you can still read and reply there. Editing and deletion may have permission or time limits.
 
 ## Account and activity
 

docs/operations/upgrading.md

@@ -40,3 +40,9 @@ Do not point a new PostgreSQL major at an old data volume. Restore a dump into a
 ## Verify
 
 Check version, pending migrations, sign-in, posting, private forums, attachments, mail, scheduled work and logs before reopening. If checks fail, use the restore plan rather than older code against the changed schema.
+
+Migration `0073_reply_draft_forums` repairs reply drafts' stored forum references
+from their live threads without changing saved content or timestamps. Updated
+thread moves and autosaves maintain these references under the thread lock.
+Apply this forward-only migration before deleting an old forum after an upgrade;
+drafts already removed by an earlier forum deletion cannot be recovered by it.

packages/db/migrations/0073_reply_draft_forums.sql

@@ -0,0 +1,4 @@
+UPDATE post_drafts d
+   SET forum_id = t.forum_id
+  FROM threads t
+ WHERE d.thread_id = t.id AND d.forum_id <> t.forum_id;