Harden

Security as a constraint on every line that touches user data, auth, or external systems. This skill is proactive: applied during implementation, not after. For reactive scans, use safe-repo (sensitive data) or deps-audit (CVEs).

When to Use

• Building anything that accepts user input
• Implementing authentication or authorization
• Storing or transmitting sensitive data
• Integrating with external APIs or webhooks
• Adding file uploads, payments, or PII handling

Three-Tier Boundary System

Always do (no exceptions)