Some more AI stuff I think warrants examination: worker escorts. England presents an example of an extreme on one end: in all my observations I don't think I've ever seen workers without an escorting unit working on the Isles, and this takes place even as nearby cities sorely need the happiness from military presence. This phenomenon doesn't seem to vary according to diplomatic situation, or really any *apparent* game state consideration. Depending on what logic is at work here, I wonder if its contributing to England's perennial problem with using their surplus of ASSAULT_SEA transports? I can proclaim confidently that fixing this could have really interesting game play outcomes, as I've under taken experiments where I've manually loaded said transports and witnessed them instantly leave harbor to go somewhere at least a little bit useful (garrison colonies, attack an indy/native city, reinforce current overseas wars).
If it helps, escorting units seem to mostly have ATTACK AI role. If I change to something like CITY_DEFENSE the unit will garrison a city and the workers will carry on. Cities don't *seem* to alter build queues in response.