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Expand-Contract Migration - CI/CD Glossary Definition

Expand-contract migration splits a breaking change into an additive expand step and a later contract step, staying compatible in between.

An expand-contract migration splits a breaking schema change into an additive expand step and a later cleanup contract step, keeping the schema compatible with both code versions in between.

This pattern is the backbone of zero-downtime deploys: expand ships first, code migrates to the new shape, then contract removes the old shape once nothing uses it.

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