Star Killing: The theory exists behind several nova bombs, anyway, and ontotechnology shows the way to interesting possibilities like twist-pinch bombs. (These are essentially the same type of nova-inducing weapon that we see at the start of Charlie Stross’s Iron Sunrise.) And one probably could induce a nova with sufficient perversion of the stellar-management technology that goes to make up a stellar husbandry framework, were one to have the luxury of building a giant industrial megaproject in the system one wanted to explode. But by and large the list of Tier 1 star-killing Instruments of Regrettable Necessity that one shall never use, by the Ley Accords and on pain of the displeasure of the entire Accord is just about empty.
Well, there is one, the star-targeted strangelet bomb. Theoretically, it should work – from the Burning of Litash, they know that the strangelet bomb itself works, and that it does burn out before destroying all matter in the vicinity, and that strangelets themselves decay and don’t irreversibly contaminate the neighborhood. But that said, no-one is exactly sure of the result of trying one out on a star, and just in case it turns out to be the nightmare case where the nova scatters active strangelets all across nearby space, no-one particularly wants to be the one to run the test.
And in any case, doing this would be an excellent way to get every major military in the Accord hunting you down, loaded for genocide. If you thought garden worlds were expensive, stars are even more so, and the collateral damage that can be caused more than a few light-years away significant.