RomRaider

Seems like my WRX EJ205 engine is toasted, because it doesen't start anymore. It worked fine until throttle position sensor went crazy (showed 0% while in reality it was 20-40%, but it worked normally with TPS 10% or so). Only drove 10km like this, because I assumed that nothing will happen, because my logic was that ECU thinks I'm off throttle, cuts fuel and runs idle timing, which shouldn't do anything too bad. For some reason AFR's went up to 16-18 for the last 100m, but I thought no harm will be made if I drive real slow in closed loop for so short distance.
Car just won't start anymore. I switched out the plugs, tested compression and found out that there's no compression in 2&4 cylinder, didn't bother to test other two cylinders. Did the compression test for the first time in my life, but don't think it's that complicated.
When I try to start the car it revs more freely and faster then usually, which according to youtube means that the engine is toasted.

Was it really because of the last 100m that AFR went so lean? Or is it possible that I missed something?

Verify your timing belt first of all.

Checked the timing belt and its all good.

free climbing engine could be vacuum leak after the throttle, or idle air control valve

how did you do the compression test?

Looks like he done it already

I did pressure test the intake (WOT if I remember correctly) and it did hold 1bar decently, so there shouldn't be any major leaks.

Did compression test by screwing it to the spark plug hole. At first I hoped there's an issue with the tester, but showed it some pressurized air from compressor and it worked like it should. Will do the test one more time just in case I really messed it up somehow. And check other two cylinders as well.

I'll try to find a way to take a look into the cylinders before opening her up. It's only around 15k km from last build

"I did a compression test" doesn't mean it was done correctly. some people do them with the throttle closed, with or without removing other spark plugs, hence asking how it was done.

I was hoping the tester was bad, but it sounds like you really got no pressure on that side. Test the other side to confirm. Sorry mate.

in the seconds before you shut it off for the last time, how was it running? ie, if you dropped compression in half your cylinders to zero, you'd feel massive shake/stumble.

Did compression test on the other side with engine belt cover slighlty off and came out that the belt is broken. Couldn't tell by looking at it and it feels strong, but after rotating the engine, belt didn't rotate. I don't know if it's even possible like that, that the belt sits firmly on the camshaft pulleys, but it's broken somewhere at the crankshaft pulley area.
Lot of belt dust in the belt cover as well.