If someone tries to publish in a published or deleted branch, give them an error page with a friendly message, telling them what happened (something like 'We couldn't save that change because your colleague xxx@example.com published this activity 12 seconds ago!') and possibly giving them a copy-pasteable field with the copy they were working on.
(As it is now, they get a generic 500 error page with a flash message telling them who published and how long ago)
If someone tries to publish in a published or deleted branch, give them an error page with a friendly message, telling them what happened (something like 'We couldn't save that change because your colleague xxx@example.com published this activity 12 seconds ago!') and possibly giving them a copy-pasteable field with the copy they were working on.
(As it is now, they get a generic 500 error page with a flash message telling them who published and how long ago)