On Kalach-9, Salt Vault Seven is a freezing oxygen-extraction vault cut through crystalline salt, where trapped regional dependents are running out of air. Ghost Element enters the vault to sabotage the secondary stack without destroying the oxygen infrastructure the prisoners — and nearby settlements — need to survive.

The trench-back colony does not hunt by sight. It listens through the salt, feeds through tube-mouths, forms crater-nurseries, and turns every footstep, winch groan, and body impact into a signal. To cross the pump room, the squad must release a captured juvenile trench-back so its distress vibrations pull the adults away and open a narrow route.

This is "Ghost Element" by Sascha Schmidt