Claude Code calls a custom statusline command every turn with a JSON payload on stdin. The payload includes the current context-window fill percentage, model, cost, and cwd. Nothing in the contract says you can only read it — you can fork it to anything you want, and the command stays a statusline. (Quick framing for anyone new to Claude Code: it’s Anthropic’s terminal CLI for Claude, and the statusline is the configurable line of text it prints under your prompt every turn — like a shell prompt for the agent. You point at any script in settings.local.json, Claude pipes a JSON object to it on stdin, and whatever the script writes to stdout becomes the visible line.)
My daemon logged 111 consecutive HTTP 429s against `https://api.anthropic.com/api/oauth/usage` over an 18-hour stretch, with zero successful responses ever in its lifetime. The poller was reading `Retry-After: 272` and ignoring it. While I was arguing with the backoff, Claude Code was pushing the same `rate_limits.five_hour` and `rate_limits.seven_day` numbers to my statusline command every turn, on stdin, for free. (Quick framing: Claude Code is Anthropic’s terminal CLI for Claude; Claude Max is the higher-tier subscription plan with weekly and 5-hour usage windows. HTTP 429 is “Too Many Requests” — the server’s polite way of saying “back off.” Retry-After is the response header that tells the client how long to wait. OAuth is the auth protocol Claude Code uses to talk to Anthropic on behalf of a logged-in user. And the statusline — the same one I covered in the statusline side-channel post — is the script Claude Code spawns every turn with a JSON blob on stdin.)