Operations
Schema evolution
Schema evolution is the discipline of changing a data structure (database table, API contract, JSON shape) without breaking existing consumers. Add fields, never remove. Default values for new fields. Versioned contracts when breaking changes are unavoidable.
More detail
In LLM-based systems, schema evolution especially matters for the JSON-mode outputs. If you add a field to the agent's output schema, every old log entry needs to be re-readable. Strategy: every schema change includes a migration that upgrades existing records to the new shape with sensible defaults.