Worked on power flow. Every aspect was problematic.
First, I had to deregister power all along the walls, including in the nearby squares. (Coverage will determine if it is possible to build there.) It took a little while get that to propagate without infinite recursion when there were connected loops in the walls, despite following the formula for powering up which did not do that.
Second, I had to figure out how to not deregister all of the power. Say, if a red-bearing wall ran parallel to a yellow-bearing wall and the creeps destroyed a link in the yellow-bearing wall. In this case, the intermediate squares lose their yellow power but not their blue power.
Third, I had to make sure that when a central tile connecting two sources was destroyed the power colors of the remaining walls matched the source on their side.
I have seen one issue in testing where the blue wasn't deregistered from walls connected only to a red source after the creeps destroyed the connection to blue, but for now that's okay.
It works most of the time, and so I think that I can move to the towers.
So I have to figure out how to do the towers.