Password reset token spec

You're asking an AI agent to write a Go function that generates password-reset tokens, emails them, and later verifies a presented token against the stored one. Write the spec that makes token generation and verification cryptographically sound. What RNG, encoding, storage, and comparison rules do you mandate, and what acceptance criteria prove it? Then describe what a naive prompt ('generate a reset token and check it on use') gets wrong — there are several traps.