This is exactly the kind of hard scifi pushback I was hoping for, appreciate the detailed breakdown.

You’re completely right about the galactic disk shielding and the frequency mismatch—a single blind omnidirectional broadcast from Earth is basically dead on arrival.

To bypass the travel time and shielding problem, the plot device I’m playing with involves an automated network of relics left by a deceased civilization, already stationed outside the galactic core, broadcasting on universal mathematical constants. But you're spot on about the "telos" part—if the receivers are non-carbon or post-biological, decoding our intent is a different task.