I like #7 - that seems very simple and does not change the rules of Widelands at all. It is still possible to conquer a portspace and burn down the port, but that is just as expensive as keeping the port.
#3 is my second favorite, but feels like an exception to the other rules in Widelands. I think it would not be super surprising in this case since ports are special anyways, but I prefer #7.
#5 is hard to implement and similar to #7 it its outcome. #4 is a special rule, and also a bit hard to implement. #6 seems to be the same suggestion, at least I do not understand the difference.
My vote is for #7: change expedition port's constructionsite to not be cancellable.
I like #7 - that seems very simple and does not change the rules of Widelands at all. It is still possible to conquer a portspace and burn down the port, but that is just as expensive as keeping the port.
#3 is my second favorite, but feels like an exception to the other rules in Widelands. I think it would not be super surprising in this case since ports are special anyways, but I prefer #7.
#5 is hard to implement and similar to #7 it its outcome. #4 is a special rule, and also a bit hard to implement. #6 seems to be the same suggestion, at least I do not understand the difference.
My vote is for #7: change expedition port's constructionsite to not be cancellable.