Cache Invalidation and Other Metaphysics

A cache is a bet that the past will keep being an adequate description of the present. Invalidation is the moment you concede the bet. The engineering question — when do we concede? — is indistinguishable from the epistemic one: how long is a justified belief allowed to outlive the evidence that justified it?

We answer it in code with timestamps and versions and eviction policies, and we pretend these are mechanical concerns. They are not. They are a working theory of how truth decays, written in a language that happens to compile.