[Skarg]

Well in our solar system there are many small bodies out way beyond Pluto, orbiting the sun. Their density is very small, but if you somehow (. . .) encased the entire system in something, many of them would eventually hit it. Worse would be any extra-solar objects and/or radiation coming in at extra-solar relative velocities... normally they almost never hit anything, but if you somehow (. . .) encased the entire system in something, they would... with a very high velocity, squared to get force...

Then there's the mass of such a thing, and how you plan on building it and keeping it in place, and/or collecting the material for it in the first place. All of those things tend to be utterly impractical even for planet-scale constructions. Also solar systems are really really really enormous - the idea of encasing one in something physical ... runs into the same problems I already have believing in planet-scale constructions, only multiplied by a number so large it's hard to comprehend, and then cubing that to account for volume... Nope to the nope power, cubed.

And one of the main problems I have with all of that, is that even if I imagine some people that can overcome all of those obstacles... then it seems to me such people would tend to have had other interests, and so be able to do just about anything, and probably would do just about anything other than that, but if they did, would also have done unimaginable numbers of other more interesting unimaginable things.

And so, if I'm thinking of a system of worlds encased in a shell from some cosmic outside threat... I'm not going to try to rationalize it in terms of real-universe engineering at all. Instead I'm going to think of alternate cosmology and metaphysics, other "planes" or holographic universes generated by consciousness etc., and/or metaphorical mythology, not real-universe science.