Scrap Armor
Scrap Armor is an artifact that, one time, gives you a full heal upon being hit 10 times, with +2 Max hull to boot. This artifact can only be obtained in the Garbage Girl Repairs event, by selecting the "Extra Spicy!!!" option.
Clarification
Upon pickup, has a counter that starts at 0 and increments when your ship gets hit (regardless of the result of that hit). When the counter reaches 10, you get +2 Max hull and heal to full, and then this artifact becomes inert, having no effect from this point on.
Strategy
Thanks to its +2 max hull gain, taking this is better in the long run than the "Uh, regular please." option. So choosing between this and the immediate 50% heal becomes a question of whether or not you'll survive to be able to take 10 more hits - if you can, this is the better option; otherwise the 50% heal is what you need to stay alive right now. Provided your build has some ability to generate Shield, there are several fights you can stall to get this to trigger immediately if you need to.
Note that the heal triggers immediately, mid-combat, when activated. So if you can activate it during a key fight, you effectively have more hull than your current maximum for this fight. Crystalline Entity happens to be a great fight to trigger this artifact - it makes a lot of low-damage shots, and its offense is initially weak (but scales over the course of the fight). So taking this into that fight (perhaps having taken a few hits beforehand) can absolutely be a winning play, and this may let you sneak a card upgrade rather than a heal before that fight if things work out.