This sounds like one of those problems where the solution is not a UX tweak but an architecture change. Perhaps prompt cache should be made long term resumable by storing it to disk before discarding from memory?

I agree.. Maybe parts of the cache contents are business secrets.. But then store a server side encrypted version on the users disk so that it can be resumed without wasting 900k tokens?

Disk where? LLM requests are routed dynamically. You might not even land in the same data center.