This question evaluates a candidate's competence in system design, distributed systems, reliability engineering, and operational concerns such as idempotency, retries, reconciliation, and SLA‑aware API design when integrating with synchronous third‑party HTTP exchange APIs.

You are designing a trading platform that routes client orders to external cryptocurrency exchanges which expose synchronous HTTP APIs (place/cancel/get). Fills and cancellations occur at the exchanges and must be reflected back to clients reliably and quickly.
Design the system and address the following:
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