Deconstruction

Your base is already built. Your job isn't to build it, it's to keep it from falling apart.

6 towers guard one path into your core. Every round, 3 of them are about to break down and you can only save 1. The other 2 decay a stage, worse defenses, more gaps for enemies to slip through. Waves never get harder. They don't need to, your own base is doing that for you.

Kill drones to earn scrap. Spend it to repair broken towers or push a healthy one past its limit. Left click a tower to overcharge it for a few seconds. Right click to open repairs. Space shields your core once a round when things get desperate.

Survive all 10 rounds with the core still standing and you win, but by round 0 you're fighting with whatever's left. Good luck holding it together.