Taking over a legacy system always starts with assessment, not coding: code quality, data structure, third-party dependencies, and documentation completeness — scored on four axes before any conclusion.
We summarize redevelopment into three models: in-place upgrade (healthy structure, add features directly), partial rebuild (keep the core, rewrite the pain points), and smooth migration (old and new in parallel, traffic switched in batches).
The three models differ greatly in cost and risk; the assessment report lays out the trade-offs and leaves the choice to the client.