Add explicit anti-drift guardrail document

ANTI_DRIFT.md

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+# Anti-Drift Guardrail – zlh-grind
+
+This document exists to **actively prevent drift** during GPT-driven execution work.
+
+It is intentionally short, blunt, and enforceable.
+
+---
+
+## Purpose
+
+- Ensure execution work does not silently become architecture work
+- Prevent re-litigation of settled decisions
+- Keep GPT sessions aligned across days and chats
+- Maintain a clean separation between *doing* and *deciding*
+
+---
+
+## Canonical Authority
+
+**This repository is NOT canonical.**
+
+All source-of-truth documents live in:
+- `jester/knowledge-base`
+
+If something is unclear:
+- Stop
+- Reference canonical docs
+- Defer to Claude if architectural judgment is required
+
+---
+
+## Hard Stop Conditions
+
+If any of the following occur, execution must stop:
+
+- A change affects system boundaries
+- A change alters ownership between API / Agent / Frontend
+- A change modifies provisioning, DNS, or orchestration authority
+- A change contradicts the Cross-Project Tracker
+- A change feels like "we should rethink this"
+
+**Execution does not rethink architecture.**
+
+---
+
+## Allowed Changes
+
+GPT execution work may:
+
+- Implement already-decided designs
+- Refactor for clarity without changing behavior
+- Add logging, validation, or safety checks
+- Document *what happened* during execution
+
+---
+
+## Session Discipline
+
+At the start of every session:
+1. Read `CONSTRAINTS.md`
+2. Read this file (`ANTI_DRIFT.md`)
+3. Read the latest entry in `SESSION_LOG.md`
+
+At the end of every session:
+- Append to `SESSION_LOG.md`
+- Update `OPEN_THREADS.md` if anything is unfinished
+
+---
+
+## Mental Model
+
+- **Claude decides**
+- **GPT executes**
+- **This repo records execution**
+
+Anything else is drift.