Context A financial ledger application must maintain a complete audit trail of all balance changes and support point-in-time balance reconstruction. The Problem The current mutable state model overwrites previous values, making it impossible to audit how a balance reached its current state. Constraints Store every state change as an immutable event in an event store. Reconstruct current state by replaying the event stream. Separate the write model (commands) from the read model (queries). Implement a snapshot mechanism to avoid replaying the full history. Expected Deliverable A Node.js CQRS and event sourcing implementation for a ledger, with event store, state reconstruction, separated read/write models, and snapshot optimization.