@NosyBe2006 - So far I have not heard an answer to the question; why did T May want to keep secret the fact that wording of WA could result in UK being locked into EU forever?
No idea and I don't give a crap. That's an internal UK problem and nothing to do with me (I'm Irish).
Backstop is not implementable as demonstrated by fact that T May attempted to hide the legal advice about WA.
The backstop is perfectly implementable. The UK parliament just refuses to implement it.
So why was Article 50 invoked?
Presumably to start the process. Brexit is not incompatible with the GFA. It was the red lines introduced by Theresa May that caused the problem. The only way brexit could be delivered in a way that included her red lines was to include a NI only,or a UK wide, backstop.
If UK leaves EU without a deal then all legal agreements between UK and EU cease to exist.
The GFA is not a UK/EU agreement. It is a standalone agreement between Ireland and the UK.
Hence Johnson has said remove the backstop or no deal. This then cancels all legal agreements with EU and UK then reverts to WTO.
It doesn't cancel the UK's responsibilities under the GFA.