When a critical finding such as a vulnerability allowing remote code execution on a critical server is discovered, the immediate priority is to inform the client's primary contact or designated emergency contact due to the potential impact on the client's operations and the risk to sensitive data. Delays in communication could exacerbate the risk or lead to an actual breach. Other choices may be part of the penetration tester's responsibilities, but the urgent communication regarding critical findings takes precedence and aligns closely with best practices in the field of penetration testing.