Right, a 15 billion meter wide beam aimed at e.g. a solar gravitational lens relay station some 542 AU out, or even aimed at much closer receiving stations arou

Right, a 15 billion meter wide beam aimed at e.g. a solar gravitational lens relay station some 542 AU out, or even aimed at much closer receiving stations around Jupiter, would not intersect Earth most of the time. At 308 nm it wouldn't be visible to ground based telescope since the atmosphere would mostly absorb it. If using gravitational lensing to set up system-to-system communication is the norm, the beam might not be bright enough to be observable by current space based UV telescopes. All of this could just be driven by ordinary post-biological-alien good engineering practices. It would seem extremely stealthy to humans, but that doesn't need to be intentional, any more than ham radio communications are intentionally stealthy against observation by whales.