The plan for first trip on the spouse vignette/visa is to fly into from USA to Belfast via Manchester, so the initial entry will be into the UK - no problems there.
We were more concerned about either of 2 different scenarios, for travel
after the initial visa/vignette trip:
(1) Travel from Northern Ireland to Republic of Ireland (border free) and then depart from Dublin airport to overseas and return to Dublin.
(2) Depart from UK airport to overseas, and return flight to Dublin.
Does the Common Travel Agreement include for non-EEA citizens who hold a UK visa? Can getting a 30 day visa stamp from Dublin to enter ROI (only for travel onward to Belfast/UK) come back to bite us, as the 30 days will expire? Or does the Irish customs/border control at the airport acknowledge the CTA and simply not stamp your passport?
I hope I've made it clear

Thanks so much for any help!!