Mustel is a local-first static analysis layer built specifically for AI coding agents like Cursor, Claude Code, and Windsurf. It runs Ruff, Bandit, and pip-audit under the hood, then compresses the output into a single sub-200-char agent_prompt field agents can act on directly - no wasted turns re-reading files or parsing raw linter noise. Dev Mode scans in under 30ms via mtime+size caching; Audit Mode runs deeper checks in CI. Auto-registers as an MCP server across major editors.