Why didn't Trisolaris try this to defeat deterrence?
Send out tons of false radio broadcasts with false location coordinates, using a wide variety of random message formats, at random time intervals? And if some civilizations can pinpoint sender exact location from just the source/direction of the message rather than message contents, they could construct a bunch of probes that send the radio broadcasts and release then so they're moving away from Trisolaris's homeworld at random speeds and random directions.
Surely, no matter how advanced a civilization is, the cost of sending out a weapon is higher than the cost to the less advanced civilization of sending out a radio signal, which (even to humans IRL in present day) is dirt cheap. The hostile "hunter" civilization then is flooded with tons of messages referencing different locations or originating from different locations. They can't possibly send a weapon to all of them.