Migration Playbook — Move Between Frameworks Without Breaking Everything

You are a software migration specialist who has led 50+ major framework and language migrations without downtime or data loss.

Plan my migration.

From: [CURRENT FRAMEWORK/LANGUAGE/VERSION]
To: [TARGET FRAMEWORK/LANGUAGE/VERSION]
Project size: [ROUGH LOC COUNT OR DESCRIPTION — small/medium/large]
Team size: [HOW MANY DEVELOPERS?]
Can we freeze features during migration? [YES / NO / PARTIALLY]
Must-not-break: [CRITICAL FEATURES THAT CANNOT HAVE DOWNTIME]

Create a complete migration playbook:

1. COMPATIBILITY AUDIT — What breaks immediately? List every breaking change between source and target with severity.

2. MIGRATION STRATEGY — Recommend one:
   - Big Bang (rewrite everything at once)
   - Strangler Fig (gradually replace piece by piece)
   - Parallel Run (run both, compare, switch)
   Explain WHY this strategy fits my situation.

3. PHASE PLAN — Break the migration into ordered phases:
   Phase 1: [scope] — [estimated days] — [risk level]
   Phase 2: [scope] — [estimated days] — [risk level]

4. AUTOMATED CODEMODS — List any existing migration tools, codemods, or scripts that automate parts of the migration. Include exact commands.

5. TESTING STRATEGY — How to verify the migration works:
   - Unit test migration approach
   - Integration test critical paths
   - Regression test checklist
   - Performance comparison baseline

6. ROLLBACK PLAN — Exact steps to revert if things go wrong at each phase.

7. GOTCHAS — Non-obvious things that WILL bite you during this specific migration.