Architecture (high level)

• A Node.js + Express backend app installed as a private Shopify app on both stores (Calgary and Edmonton).
  
• Use Shopify Admin API + Shopify Webhooks to catch and react to events. Core webhook events subscribed: orders/* (created, updated, cancelled, fulfilled), inventory_levels/*, products/* (created, updated, deleted), fulfillments/*
  
• A synchronization engine that:
  
  • Normalizes incoming events into a canonical change (product change, inventory delta, location-change event).
    
  • Applies deterministic rules to update the other store(s): e.g., product creation in Calgary => create product + variants in Edmonton; inventory delta at location X => update inventory level in partner stores at the corresponding location mapping (Calgary, Edmonton, AQ Warehouse).
    
  • Handles idempotency & retries (webhook dedup, exponential backoff) and stores event receipts to avoid double-updates.
    
• Location mapping & master rules: a small configuration layer defines which Shopify Location IDs correspond to Calgary / Edmonton / AQ Warehouse across both stores. That mapping is used to route inventory updates.
  
• Reconciliation & audit endpoints: periodic background job or on-demand endpoints produce diffs between expected inventory and live store inventory to surface mismatches.
  
• Manual override tools for operations to accept/reject automated sync changes and re-run fixes for batches of SKUs.
  
• Security: HMAC validation for webhooks, OAuth or private app credentials scoped to necessary Shopify APIs only. Logs persisted for 90+ days for audit.
  

Key technical components

• Node.js + Express server with webhook route handlers.
  
• A message queue (in-process queue or persistent job queue) to serialize and reattempt synchronization tasks reliably.
  

Administrative UI (optional) or REST endpoints to view sync status, conflict logs, and mapping config.