Dockerfile Layer Caching: Why Every Build Reinstalls Everything
Your Dockerfile copies the lockfile before the source, and CI still reinstalls every dependency on every commit. That gap between a correctly ordered Dockerfile and a build that behaves as if it isn't comes down to five distinct failure families: ordering traps, a build context that poisons checksums, a cache that never reaches CI, cache mounts that vanish with the runner, and multi-stage export modes. Here is how invalidation actually works and how to prove which one is costing you.
