What 123 million simulated CS2 case openings taught me about modeling RNG

I run case-sim.com, a free CS2 case opening simulator. As of this week the global counter ticked past 123 million openings. That's a weirdly humbling number — it's also enough rolls that any subtle bug in my probability code would have been screaming at me for years. I want to share what I actually learned building this thing, because most "how to model case openings" tutorials I've seen are wrong in at least one quiet, important way. If you're building anything with weighted RNG — loot tables,