So, the next step is to understand "phase" or "polarity" of your DCC system to answer your next question.
Even though the "Waveform" on the rails is square, rather than a sine wave, what is on the rails is like the AC you feed your home and appliance outlets.
So, while there is no "polarity" as in plus or minus (as the polarity is changing many times a second),
there IS a "phase". This means if you have 2 boosters, for example (and they are running the same voltage), then you CAN connect them together if they wired such that the are both in phase, i.e. their Alternate Currents are "synchronized".
So finally to your question... when a loco or powered car is straddling an "insulated" break between power districts, if they are in phase, everything is fine.
If they are not, you indeed will have a short.
For track in a loop, for example, no problem, wired right once, is always right.
But there are layouts that have a section where the track plan can effectively connect the right rail to the left rail. even insulating the sections would cause a short when the loco wheel spans the insulating gap, or a powered car does this.
In this case, you have a "reverse loop", and there is a nice component called an "autoreverser" that will detect the short (polarity/phase mismatch) and REVERSE the connections on the autoreverser side and everything is fine. The electronics work so fast that the short circuit is very short in duration and you (and the locomotive) don't even notice it.
As long as the entire train is in the reversing section, then reversing the phase/polarity in that section causes no issue (the locomotive goes the same direction regardless of the phase/polarity.
Basically no fuss,, no muss.
So, you isolate power districts from each other. They can have separate boosters, or perhaps come from the same booster and have separate circuit breakers. The power districts that could have a phase/polarity issue need an autoreverser.
It's actually quite simple and very flexible. Like I said I have 4 boosters, and I do have an autoreverser, I have a WYE leading into my switchyard, which inherently causes a "reverse loop" (mind that not all reverse loops look like a loop).
This is as clear and concise as I can make it, hope it helps.
Greg