Caching speeds repeated input
Prompt caching helps reuse already-processed prefixes. It does not decide what matters, store durable facts forever, or update the project's source of truth. It is a performance feature, not a memory system. A warm cache feels like memory until it expires, the prefix changes, or the model is replaced — then the illusion vanishes.
Use each layer for its job
Cache for repeated static input. Memory for durable facts and user preferences. Handoff for current task state. Retrieval for source material loaded by pointer. The window for active work. Confusing them is how systems become fragile in ways that defeat root-cause analysis.
The drift to remember
If your system 'remembers' a fact only because the cache is warm, you have a latent bug. The right test: clear the cache, restart the session, and see whether the fact still surfaces. If not, that fact needs a real home — durable memory or an explicit handoff — not just cached context.