Have the tool maintain a doc, and use either the built-in memory or (I prefer it this way) your own. I've been pretty critical of some other aspects of how Claude Code works but on this one I think they're doing roughly the right thing given how the underlying completion machinery works.

Edit: If you message me I can share some of my toolchain, it's probably similar to what a lot of other people here use but I've done some polishing recently.