Adversarial PRD review using 5 specialized subagent personas. Probes for ambiguities, hidden complexity, and untestable requirements before execution begins. Use when: user says 'review this PRD', 'critique this spec', 'is this PRD ready', 'adversarial review', or when /prd-writer invokes it at Step 7. Also trigger when user shares an existing PRD and asks if it's implementation-ready.