I built kerf-cli because Claude Code told me not to worry about cost

A few weeks ago I logged into Claude Code, typed /cost , and got back this: With your Claude Max subscription, no need to monitor cost. Two days later I had used 91% of my weekly limit in a single morning of work. I had no idea which session, which project, or which model was responsible. I tried ccusage (which is great) and it gave me totals — but I wanted to ask questions like "which of my projects is eating Opus tokens unnec