stetkeep stops Claude from refactoring code that's intentionally the way it is. Two pillars: 1) XML-structured behavior protocols (BRAIN/CRAFT/PERF, ~1.8K tokens each) encode routing, refactor discipline, and measurement-first performance rules using the XML tagging pattern Anthropic's prompting guide recommends for reliable parsing. 2) A 16-entry false-positive catalog of patterns Claude commonly mis-flags as anti-patterns: 1000-line constants files (not God Files, just data tables), V8-optimized .map().map().map() chains, below-fold <img> tags, useMemo that fixes reference-equality bugs. No other plugin in the directory ships this. Enforcement is mechanical, not prompted: permission deny-lists, PreToolUse hooks (safety-net.sh / .ps1), tool-scoped subagents that cannot Write new files, and path-scoped rules that auto-load CRAFT/PERF on src/** access. Honest 5-layer breakdown in ARCHITECTURE.md §1. Supply chain hardened: zero runtime dependencies, OIDC Trusted Publisher (no long-lived npm token), Sigstore SLSA v1 provenance on every tarball, GitHub Actions pinned by commit SHA. Coexists with existing CLAUDE.md and memory/ without overwriting. Distributed via npm (npx stetkeep install) and the self-hosted Claude Code plugin marketplace. MIT license.