claude-code-extension-engineering

Architecture decision reference for Claude Code extensions: which mechanism should own a behavior, why the nearest alternative is wrong, and what the choice actually guarantees. Selection guide, 28 composition cards, 31 hook-event contracts, dated version gates, machine-checked evidence ledger. Benchmarked, both results published: 44 percent unaided versus 100 percent with the reference, and a NULL on architecture decisions (21 to 20 versus docs alone, p=1.000).