repeated cache bust for every image after 50th #5238

Describe the bug

The Copilot CLI has a 50 image limit per session.
On the 51st image, the 1st image is removed from the cache.
Removing 1 image image triggers a full refill of the cache.

It gets very, very expensive, as you would expect.

Affected version

GitHub Copilot CLI 1.0.103

Steps to reproduce the behavior

Create a big context, analyze 50 images, then analyze 1 more and observe the cache refill.

Expected behavior

Cache-friendly image expiry.

Additional context

My specific use case was driving a VNC session.
Several cost friendly workarounds are pretty obvious, but I wasn't even aware this was happening so I didn't apply such strategies.