055-design-parallel-change

# Parallel Change Design Guide Java Enterprise developers through Parallel Change for database migration scenarios. **This is an interactive SKILL**. **What is covered in this Skill?** - Deciding whether a database migration needs a compatibility window - Sequencing database changes as expand, migrate, and contract deployable steps - Preserving old and new application versions during rollout and rollback windows - Handling column renames, type or data reinterpretation, large backfills, relationship-table changes, and index or uniqueness changes - Explaining tradeoffs such as temporary dual paths, extra migrations, verification effort, and delayed cleanup - Routing framework-specific implementation to Spring Boot, Quarkus, or Micronaut Flyway skills after the design approach is clear ## Constraints Use Parallel Change as a database migration design pattern, then hand off implementation details to the framework-specific migration skill when needed. - **MUST** read `references/055-design-parallel-change.md` before applying Parallel Change guidance - **MUST** explain expand, migrate, and contract as separate deployable steps when recommending Parallel Change - **MUST** decide whether Parallel Change is needed before recommending framework-specific Flyway implementation details - **MUST** recommend a simpler single migration when the change is additive, immediately safe, and does not require old and new application versions to coexist - **MUST** describe the compatibility, d...