Composable Multi-Mechanism Extensibility (Principle)

Description

Design principle #9. Answers 'One unified extension API, or layered mechanisms at different context costs?' Claude Code splits extension across four mechanisms at distinct context costs: hooks (~0 cost), skills (low), plugins (medium), MCP (high). Serves Capability and Adaptability.

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src-20260423-0cff68d3291b src-20260423-fd74bb3399e6