[AnderRV]

Why

The agent signup endpoint can now ask one short question before it creates an account (HTTP 428, challenge_required). The CLI only showed that as a raw body in cause:, so an agent had no clear way to answer it, and every CLI run is a new process with no memory of the question.

What changed

• A 428 challenge_required becomes the error SIGNUP_CHALLENGE. The message carries the question, next_action says to run zenrows signup --answer "<your answer>" and then re-run the original command, and --json adds error.challenge (id, question, expires_at).
• The pending question is kept in .zenrows/signup-challenge.json (no secret: id, question, expiry, and the signup URL that asked it). The file is added to the workspace .gitignore list.
• New zenrows signup --answer <text> posts {challenge_id, answer} to that URL with the usual signup headers. A right answer stores the key and account exactly like auto signup, prints the claim link and says to re-run the original command. A wrong or late answer stores and shows the new question. A 429 challenge_locked becomes SIGNUP_CHALLENGE_LOCKED with retry_after. No pending or an expired question gives SIGNUP_CHALLENGE_MISSING without a request.
• A question or the lock stops the signup endpoint fallback loop, since both are real answers from a working endpoint. Other statuses (429 rate_limited, 503, network errors) behave as before.
• zenrows signup without --answer is unchanged. Help text, README and the zenrows skill describe the question and how to answer it.

How tested

• npm run typecheck passes.
• npm test: new tests/signup-challenge.test.ts covers 428 parsing and persistence, --json shape, ensureApiKey, right / wrong / locked / none pending / expired answers, signup --answer --json, and a non-challenge 428. Existing signup tests (201, fallback, 429 rate limited) pass unchanged.
• End to end against a local backend with the question enabled: zenrows fetch showed the question, a wrong answer showed a new one, the right answer stored the key and account, and a second --answer reported no pending question.