Engineering write-ups from building Game Combiner — mostly about the gap between a system that looks correct and one that actually is. Every number here came from production.
A player saw the same number on every result and asked whether anything lands close to zero. The number was right. The scale printed beside it was unreachable, and had never once been observed.
Three strangers told us the recommendations were bad. We had probes, invariants, and a 600-pair audit that said otherwise. All three were right, and none of our internal tests could have found what they found.
Combining with Rust kept surfacing games with “Rust” in the name. Minecraft’s eight nearest neighbours were all Minecraft ports. The vector was partly a string match on the title.
We shipped a “dead multiplayer” warning that flagged Overwatch 2 while 61,499 people were in game. Absent data had been read as a measurement of zero.
Two thirds of our games had tags. The other third competed with no descriptors at all — invisible as answers and starved as vectors. Re-downloading the dataset added exactly zero.