When an AT migration is cancelled, post GUIDs will be invalid leading to issues with feeds #86334
Description
Found investigating this #84045
Investigation is summarized in this comment p9F6qB-dHO-p2#comment-57292.
Problem
In sumamry users site had been migrated to the Atomic platform, and then the migration was cancelled/reverted.
Posts have GUIDs of the form https://$site.wordpress.com/?p=$post_id. These "GUIDs" are then included in the RSS feed available at https://$site.wordpress.com/feed. When the site's feed is processed by reader, the "GUIDs" are used to extract the $post_id.
The problem is that if these "GUIDs" were created on the Atomic platform site, the post_id contained in them no longer matches the post_id from the simple site.
This leads to the posts being filtered out of subscribers' feeds.
If the user were to make a new post, that would appear as normal.
Solution
I think we should add some code to the AT revert process which goes through and re-computes post GUIDs to use the newly created post_id's for the simple site.