Add execution constraints to prevent drift

CONSTRAINTS.md

@@ -0,0 +1,18 @@
+# Constraints – zlh-grind
+
+This repository is strictly for **GPT execution work**.
+
+## Hard Rules
+- Do NOT make architecture decisions here
+- Do NOT redefine system boundaries
+- Do NOT duplicate canonical documentation
+
+## Source of Truth
+All architecture, decisions, and authoritative docs live in:
+- `jester/knowledge-base`
+
+## Role Split
+- Claude: architecture, decisions, control-plane changes
+- GPT: execution, implementation, logging, reasoning
+
+If a change might affect architecture, stop and defer.