A few gigs of disk is not that expensive. Imo they should allocate every paying user (at least) one disk cache slot that doesn't expire after any time. Use it for their most recent long chat (a very short question-answer that could easily be replayed shouldn't evict a long convo).

Whats lost on this thread is these caches are in very tight supply - they are literally on the GPUs running inference. the GPUs must load all the tokens in the conversation (expensive) and then continuing the conversation can leverage the GPU cache to avoid re-loading the full context up to that point. but obviously GPUs are in super tight supply, so if a thread has been dead for a while, they need to re-use the GPU for other customers.