How does attack module durability drop in Egg Heist?

The drain is flat: every black hole or control skill you fire takes one tick, whatever it hits. There is no discount for a skill that whiffs, so the module rewards picking your moments rather than casting on cooldown.

That matters because the attack module is the piece that lets you deal damage in Egg Heist at all, on top of raising the damage you do. Spending it freely in the early rooms can leave you short when you need it most, such as clearing a path once someone has dug out the central egg and is carrying it to the boat on the beach. Running dry partway through a raid is a real risk, so treat each skill use as spending a resource you cannot top up on a whim.

In practice: save your offensive abilities for fights that block the route or protect the egg carrier, and avoid trading skills against targets you could simply walk past. If the module is already low, plan the rest of the run around reaching extraction instead of chasing extra loot.

Not settled: How much durability an attack module starts with, and exactly what your damage does once it reaches zero, are not settled.