Is apparently a thing. Area reclaim commands will now reclaim any enemy units that get in the way. Combat fab squads aren't very useful because they preferentially reclaim their fallen comrades, but expanding fabbers that find an enemy mex field have an easier way to clean it up. I presume this is a vestige from an earlier fab-based Locusts.
This had nothing to do with locusts -- and everything to do with precisely the nefarious uses you're imagining. A few fabbers together stand a pretty decent chance against a lone patrolling dox if you respond to the notification promptly. It'd be nice to get the preferences switched around so they go for live enemies first, but that would've been a much larger chunk of work. (An even larger chunk of work that we've wished we could tackle: Having it automatically reclaim if you build over enemy structures. I'm told it would require too much work on the task system.)
That's a pity. It's only relevant when building mexes in enemy territory, but it's still infuriating. You have to wait until the enemy mex is dead to even give the orders to build yours in that spot T.T
You can work around that, I think. If you give the reclaim command by clicking on the enemy mex and then queue up an area build command for building the mexes.
The problem is that player usually doesn't know there is already the enemy metal extractor. If the player doesn't keep an eye on his fabricator, the fabricators skip the metal spot and move to the next one location. Let fabricator automatically clear enemy structure and build a new one over there is much more convenient.
You can't queue building a mex where there's an enemy mex. If you try to reclaim and queue an area build your fabber will not build any mexes where enemy mexes are.
It makes sense to automate the fabbers reclaiming something that's in the way of what you've told them to build. But ideally, you should have a fabber out on its own without an offensive unit.
I just tested it. It does work. So I select a fabber, then I right-click on the enemy mex to start reclaiming it, then I click the mex in the build menu of the fabber and drag a circle over the mex I am reclaiming while holding shift to queue that command. Once the fabber is done reclaiming the enemy mex, it starts building a new one.
Just tested it, seems like you can actually do it, but it only works if the area build command has an unbuilt metal deposit inside it. If you try to do it with a single mex you can't. It also works with area reclaim ^^
Is it possible to get some more technical insight into the problem? I think there is much to learn from such kinds of limitations
It basically comes down to the way the server and the client decide where you can build, and the fact that both have to be rewritten and retested (testing is usually the harder part, to be honest) to make it so that they both agree that you can build on your enemy's structures but not on your own, when you first issue the command; but then the server has to be able to turn that into a reclaim command when the fabber is actually ready to start building. That's fine; we do that kind of thing all the time. (An attack command, for instance, gets turned into a move command internally until the unit is in range.) Then we come to really hairy issues, like making sure everything behaves right when alliances change or if someone else rushes in and starts building something new there before you do, and getting fabbers to cooperate right when multiple build orders suggest that they ought to be building the same thing. (This is on the list of nice things to have, too, but when there's so much Cool Stuff left to try to get done, it just doesn't make sense to put a massive engineering push into rewriting a system that's working pretty well.)