Shield alternative concept

That's also an option, yeah, but what I was envisioning was something with a lot more armor than an engineer, so that compared to, say, four engineers, it has about as much health but retains full build capacity right up until it dies.

I do really, really like the idea of circular 'standing orders', though, and agree that depending on implementation that could make my suggestion obsolete. In fact, you might be able to expand that and combine it with control grouping to explicitly mark out your bases so that from a view of multiple planets you can give entire bases higher-level orders; tell them to slowly expand, or to defend themselves, or to prioritize construction of certain unit types over others, etc.