Senior Laravel Developer — Fix Inventory Race Conditions and Ensure Data Consistency

Our application allows multiple users to reserve products from the same inventory. Currently, if two requests arrive at almost exactly the same time, both may read the same available stock and successfully reserve more items than we actually have. We need to make inventory reservations completely safe under concurrent requests. Requirements Implement a concurrency-safe inventory reservation mechanism using Laravel and MySQL. Prevent stock from becoming negative under any circumstances. Handle multiple simultaneous requests for the same product correctly. Use database transactions and appropriate locking or atomic updates. Implement idempotency so retrying the same request cannot reserve stock twice. Ensure strict tenant isolation: one tenant must never access or modify another tenant's inventory. Return appropriate API error responses when stock is insufficient. Write automated tests covering concurrency, duplicate requests, and tenant isolation.