Idempotent Redundancy

• ›When adding redundant paths (fallbacks, belt-and-suspenders), make them idempotent.
• ›Pattern
• ›Redundancy without idempotency causes loops, churn, or data corruption.
• ›DO
• ›Use _is_merge: true for Braintrust updates
• ›Check if value exists before writing (fallback only if missing)
• ›Use atomic write/rename for file operations
• ›Make reconciliation steps safe to run repeatedly
• ›DON'T
• ›Write unconditionally in fallback paths
• ›Allow multiple writers