H.6.2 Migration Strategy

Broad visibility makes a large change possible; it does not make one atomic commit safest.

• Use an atomic change only when discovery, review, validation, landing, and revert fit one coherent state.
• Use expand-migrate-contract when APIs, schemas, configuration, data, deployments, or external consumers create real skew.
• Shard work when one diff exceeds review, CI, merge, or recovery capacity while preserving a global transition state.
• Separate source-change size from runtime rollout blast radius.
• Define fallback, partial recovery, conflict handling, and the authority to stop or reshape the migration.