12.15 Security Design Principles Summary

mindmap
  root((Security Design))
    Defense in Depth
      No single layer bypass is fatal
      Each layer operates independently fail-closed
      Multi-layer architecture covers the full chain
    Secure by Default
      default mode requires confirmation
      bypassPermissions requires explicit opt-in
      Sandbox off by default (opt-in)
      deny and safetyCheck take priority over bypass
    Extensible
      Hooks enable programmatic approval
      Rule system supports wildcards
      Enterprises can customize security policies
      policySettings has highest priority
    Auditable
      Every decision records its source
      Telemetry events fully recorded
      PermissionDenied Hook for auditing
    Mistake-Proof
      200ms grace period to prevent accidental triggers
      dangerouslyDisableSandbox naming
      Denial tracking prevents infinite loops
      AI explainer assists decision-making
    Progressive Evolution
      tree-sitter shadow testing strategy
      Observe first then switch
      Telemetry-driven security decisions

Looking at the entire permission and security system, its core design philosophy can be summarized as: every layer assumes the other layers may fail. The AST parser assumes regex checks may be bypassed, so it operates independently; path constraints assume command analysis may miss things, so they check independently; user confirmation assumes all automation may fail, so it serves as the final safety net. This "pessimistic but pragmatic" design mindset is the fundamental methodology for building security-critical systems.

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Hands-on Practice: In claude-code-from-scratch's src/agent.ts, search for permission-related code to see a minimal "confirm before execution" implementation. Compare it with the defense-in-depth architecture in this chapter and consider: what are the minimum security layers a minimal Agent needs? See the tutorial Chapter 5: Permissions and Security.

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