dnqbob

> Thanks to HPF determining wether a cell is reachable shouldn't be that performance intensive. It should actually be fairly cheap. HPF does help on terrain stuck, but `MoveWithinRange` is...

> There are plenty of situations like that where the player will assume that the game is bugged for cancelling, there needs to be a better thought out solution. Actually...

> It already works like that for move orders onto impassible terrain. No. In OpenRA the unit will just stop, instead of get as closer as possible. Actually, "get as...

I am not going to push this PR any further because this PR is an attempt to find out where we need to fix if we want to fix https://github.com/OpenRA/OpenRA/issues/21187....

I strongly suggest to make a new PR instead of stick to this PR which makes the code hard to understand and messy.

Like @RoosterDragon said, I think we should do something to keep the code clearly at new PR. 1. Make a list on expected behaviors when they cannot reach the destination....

In previous consideration of `Activity` base on a fact that OpenRA only need to know if current (child) activity is finished, but now we need to know how it is...

This issue (Production UI upgrade) has some very nasty side effect on fixing. You need a test on owner change before/after disable or enable. There can be some bugs that...

> In case of OpenE2140, the building should not be usable while its being constructed. I hope this PR can overcome the problem I met and mentioned above, but if...

Add: This PR is also very worthy for the mods that can switch mutiqueue production or singlequeue production in gameplay, if you can make it.