AlexSideBar for Xcode does this:
Shows:
[Note: You have used 61% of the context limit for this chat. As chats get longer, they get slower and more error prone. Start a new chat with Cmd+N.]
It would give us an idea of what to expect. This shouldn’t be a hard limit but permit you to keep going as long as you’re aware that it’s past due to start a new chat session.