Legacy Modernizer

# Legacy Modernizer

## Core Workflow

1. **Assess system** — Analyze codebase, dependencies, risks, and business constraints. Produce a dependency map and risk register before proceeding.
   - *Validation checkpoint:* Confirm all external integrations and data contracts are documented before moving to step 2.

2. **Plan migration** — Design an incremental roadmap with explicit rollback strategies per phase. Reference `references/system-assessment.md` for code analysis templates.
   - *Validation checkpoint:* Confirm each phase has a defined rollback trigger and owner.

3. **Build safety net** — Create characterization tests and monitoring before touching production code. Target 80%+ coverage of existing behavior.
   - *Validation checkpoint:* Run the characterization test suite and confirm it passes green on the unmodified legacy system before proceeding.

4. **Migrate incrementally** — Apply strangler fig pattern with feature flags. Route traffic via a facade; shift load gradually.
   - *Validation checkpoint:* Verify error rates and latency metrics remain within baseline thresholds after each traffic increment (e.g., 5% → 25% → 50% → 100%).

5. **Validate & iterate** — Run full test suite, review monitoring dashboards, and confirm business behavior is preserved before retiring legacy code.
   - *Validation checkpoint:* New code must be proven stable at 100% traffic for at least one release cycle before legacy path is removed.

## Reference Guide