D10. Agent interface: MCP + short skills + AGENTS.md

30 MCP tools with JSON Schema inputs (no Zod), read-only annotations and a read-only mode; every write is validated, journaled and undoable, and returns the diagnostics it caused. Four short skills written by hand (SkillsBench: curated short skills help, generated ones hurt) and an always-loaded AGENTS.md index of the critical rules (Vercel: skills alone were not invoked in 56 % of cases).