I'm a Saudi passport holder with permanent residence in the United States, and I'd like to book a flight from Washington to Edinburgh with a three-hour layover in Dublin. I know there's a Common Travel Agreement between the Republic of Ireland and the UK, and so I was wondering if I need an Irish transit visa to connect to a flight from Dublin to Edinburgh, or if a UK visa is sufficient. And are there any users who traveled US-RoI-UK under the same circumstances with needing a UK visa who can share their experience? Users who aren't visa-free for the UK or Ireland, that is.
From what I've read in these forums and others, it seems like Irish immigration in effect does controls on behalf of the UK government unofficially.
I have also heard concerns from people saying Aer Lingus employees could deny me boarding depending how confused an employee would be when looking up visa requirements on TIMATIC.