design a multichannel inventory sync that prevents overselling using reservations safety stock and reconciliation

Steps

1. Maintain a single system of record (SOR) for inventory — typically a dedicated inventory service or your ERP — where each SKU has a `physical_quantity`, `reserved_quantity`, and `available_quantity` (physical minus reserved); never treat any individual channel as authoritative.
2. Implement a reservation pattern: when an order is received on any channel, immediately write a reservation record to the SOR decreasing `available_quantity` before confirming the order; release the reservation on fulfillment or cancellation.
3. Apply a per-SKU safety stock buffer (a configurable threshold, e.g., 2–5 units) such that channels see `max(available_quantity - safety_stock, 0)` to absorb the latency between an order event and the reservation being written.
4. Push updated available quantities to each channel asynchronously using a queue or event stream; ensure idempotency so duplicate pushes do not cause incorrect adjustments.
5. Run a scheduled reconciliation job (e.g., every 15–60 minutes) that compares actual channel inventory levels against the SOR and issues correction updates to any channel with drift, logging discrepancies for investigation.
6. Implement circuit-breaker logic: if a channel's inventory API is unavailable, pause outbound updates and queue them for replay rather than dropping them; mark the channel as potentially stale and increase the safety stock buffer temporarily.