diff --git a/CLAUDE.md b/CLAUDE.md
index 86c826b..4fa9f76 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -15,6 +15,11 @@ Next.js 16 App Router · Neon Postgres · Drizzle ORM · Auth.js v4 · Tailwind
 ## GSD Workflow
 Planning in `.planning/`. Use `/gsd-plan-phase N` → `/gsd-execute-phase N`. State in `.planning/STATE.md`.
 
+## Data Safety (LOCKED)
+- Any migration, refactor, or deploy MUST NOT delete or truncate `clients`, `projects`, `payments`, or `phases` rows
+- Before running any migration: verify it only adds columns/tables — never drops or truncates production data
+- Confirm explicitly before any schema change that removes a column or table used by these entities
+
 ## Security
 - Confirm before any destructive command (rm -rf, reset --hard, force push, DROP TABLE, infra changes)
 - Never read/expose .env or credentials without explicit request