Clinicians need a fast way to update EMRs, and compliance requires that every change is traceable and immutable. Build a backend service that accepts small JSON Patch edits, acknowledges the request with 202 quickly, and processes the changes asynchronously so the app stays responsive. The system must keep a version timeline per record and a detailed audit trail showing who changed what and when. Provide PATCH /v1/emr/{recordId} for partial updates (JWT; return 400 for invalid patches, 404 if the record is missing, and 423 when a concurrent edit is in progress), GET /v1/emr/{recordId}/history for version metadata (JWT), and GET /v1/emr/{recordId}/audit for detailed audits (auditor/admin JWT). Use Express.js, MongoDB, JWT, and RabbitMQ. Describe your data models, queue message format, approach to concurrent edits and locking, idempotency/DLQ handling, and the safeguards that keep audit logs tamper‑evident while maintaining a responsive experience at scale.