The Legacy Modernization Planner

Help me plan the modernisation of this legacy system.

The legacy system: [DESCRIBE WHAT IT DOES AND ITS PROBLEMS]
The risk of leaving it: [DESCRIBE]
Constraints: [IT CAN'T GO DOWN, BUDGET, ETC.]

Provide:
1. The real cost and risk of the status quo (often underestimated)
2. The modernisation options (replace, re-platform, wrap, rebuild) and
   trade-offs
3. How to do it incrementally to avoid a risky big-bang cutover
4. How to manage the transition without breaking the business
5. The recommended approach and sequence

Favour incremental, lower-risk paths over big-bang replacements, which
frequently fail. Flag where deep technical assessment is needed.