I thought the contingency wanted to save the galaxy from a possible internal threat caused by the civilizations within it...so blowing up stars seems counter point to that outside as the very last option where it would be ensured to fail otherwise. That then runs the issue of not being engaging.
No: their goal is to save the universe.
When they spot a society capable of building a type 30 singularity, they are supposed to cleanse it, because T30 singularities destroy the entire universe.
Destroying stars or entire gaalxies is a small scale problem next to what they are trying to solve. And they are built by aome crazy advanced ancient society.
They glitch and replace their activation trigger: in my headcannon this makes them less effective. Each of their planets is putting out pretty huge fleets every year: I imagine if they functioned properly, they'd notice the incoming singularity threat and build up a pile more before starting the attack.
My "black hole starbase" idea was just a way to make the fight more interesting and impactful.
The contingency fight is a 2 phase one. Phase 1 is conment being able to defeat a single wandering fleet.
Phade 2 is reduction: being able to defeat their hib defence fleet.
And once you hit phase 2, the rest is mop up.
There is a risk of fighting 2 fleets or a hub fleet and a wanderer and losing your fleet.
It would be good if the plot lasted longer somehow. And making black holes and harvesting them might do that.