Shared Neutral Fix?

Not a great pic, but I tried to tape the wires from each cable together to show what's going on (3 cables total).

I have a three-way-switched light fixture (cable marked with red marker on tape) with two cables from a different circuit passing through the box. The cable to the fixture has a capped white that reads as hot and a black going to the fixture. The neutral from the fixture then taps into the other circuit (seems like a shared-neutral/MWBC situation).

Anything I need to do other than add a tie to the breakers at the panel, so that the two circuits shut off at the same time?