any reasonably large, well
populated system with resources worth fighting over will divert at
least SOME of those resources to basic security concerns, like knowing
who is in their yard, and keeping track of when they arrive and
depart.
The closer the BG gets to any place interesting, the more likely it
will pop up on someone' occlusion monitor. Still, space is big. You
never know.
>Just to clear something up, there is SPACE and there is space, just like there is BLUE ocean, and green ocean, a.k.a 'the littoral'
So any reasonably large, well populated system with resources worth fighting over is not going to be a pristine island-of-a-world in a three-planet system. It is very likely the system will be with several more planets, not a few moons, and besides that a heap of other 'stuff' like derelict ships and stations and bits of abandoned space exploration and resource extraction equipment that authorities are still looking for owners of to charge fees for abandonement in-system, and odd mined, semi-mined and unmined slabs of 'rock', and 'rock' used by the wealthy for their own orbital retreat fortresses, and etc. etc. etc.
In other words there isn't a need for an 'umbrella'. A system surveillance will produce the system 'terrain' not quite immaculate for the sensors to scan, and with quite a significant number of objects to use as screens.
And then there is bribary and corruption.
After all, there must be corruptable individuals somewhere in the sensor comand structure, and assured that their job won't be blasted out of existence, they may well turn a 'blind sensor' to the certain Jump coordinate for long enough.
This is before considering other forms of deception.
Greg