v4.0.0 — Karajan Environment: your agent orchestrates, Karajan governs

Major. Karajan becomes an ENVIRONMENT that attaches to the agent you already work with (Claude Code or Codex). kj env install writes the method into your agent's rule file from one source — RAG before coding, card first, TDD, cross-AI review before committing. kj review --staged routes every diff to an AI different from your orchestrator and records the verdict tied to the sha256 of the exact diff. kj review --install-gate turns it into a git pre-commit gate: without an approved cross-AI verdict, the commit does not enter — a false green becomes structurally impossible. RAG-first with drift updates, state_backend (HU Board | Planning Game), and the classic subprocess pipeline continues as the headless mode stamping its reviewer's verdicts. karajan-code itself runs under its own environment. Full notes in the CHANGELOG.