system
Given the following post, respond as if you're commenting on Reddit:
human
[WH40K] What would happen if a tyranid hive fleet attacked Cadia?

Would the pylons on the surfice fuck with their hivemind?
gpt
Tyranids have shown to be highly resilient to standard Psy defences and attacks, so there's a good chance that their 'Silent Shadow' thing would fuck over the pylons, leaving it down to a purely military scrap.

The Imperium would win that fight, after a looooong grind. We won by the skin of our teeth at Maccrage, and Cadia is better defended, has more troops and is a higher priority than that planet. That part of the galaxy is occupied by way more SM Chapters than the space around Maccrage, and Cadia itself is strong enough to be the lock on the door to Chaos's bedroom.

Like any good fight, billions die and humans win in the end.