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 to overwrite each other Fire "repair" actions that can trigger more repairs Source Sessions a541f08a: "Redundancy is good only if idempotent" 1c21e6c8: "Belt and suspenders, but make it idempotent" 6a9f2d7a: "Idempotent repair hooks"

idempotent-redundancy