Hono Router with Cloudflare D1 Transaction Handler

Build a secure edge API endpoint using Hono router and Cloudflare D1 SQL database implementing a nested multi-query database transaction. Details: - Handle checkout flow logic: verify stock level, insert order record, deduct user balance, and update stock count in a single secure atom transaction - Implement error rollbacks if any step fails during execution - Use Zod schemas to strictly validate the payload - Return clear API response codes conforming to REST standards.