Every team eventually says the same sentence about its own system: nobody knows why it does that any more.
The code is still there. It compiles, it ships, it serves traffic at three in the morning. What has gone is the knowledge that produced it. The rule someone agreed with a customer four years ago. The constraint that forced an architecture decision. The reason a strange workaround exists in the payment path. That knowledge lived in people, and it left when they did.
What remains is a fossil: evidence that a decision happened, without the decision itself.
We accepted this because, until recently, code was the only durable artifact that could actually run. Documentation was a courtesy. Specifications were scaffolding you threw away once the building stood. Anything that was not code decayed, because nothing depended on it being true.
I have spent the last while testing whether that is still the case. This post is what I found, including the parts that did not work.
