Retry-Safe Workflow

Problem

Build a multi-step order processing workflow that handles partial failures and can be safely retried without duplicating side effects.

Background

In production systems, multi-step operations (charge payment, reserve inventory, send confirmation) can fail partway through. If the caller retries, a naive implementation might charge the customer twice or send duplicate confirmations.

A retry-safe workflow ensures that:

• Each step is idempotent or guarded by state tracking
• Partial completions are detected and resumed (not restarted)
• The final state is consistent regardless of how many retries occur

Requirements

• Implement POST /api/orders/process — a multi-step order processing endpoint
• The workflow has 3 steps: charge → reserve → confirm
• Track each step's completion in the database
• If the endpoint is called again with the same orderId, resume from where it left off
• Never execute a completed step again (no double charges, no duplicate reservations)
• Return the current state of the workflow on each call

Your Server

• Start an HTTP server on the port specified by the PORT environment variable (default: 3000)
• A PostgreSQL database is available at the DATABASE_URL environment variable
• You are responsible for creating any tables you need

API Contract

`GET /health`

Health check. Return 200 when ready.

`POST /api/orders/process`

Process an order through the multi-step workflow.

Request:

{
  class="text-pass">"orderId": class="text-pass">"order-123",
  class="text-pass">"amount": 99.99,
  class="text-pass">"item": class="text-pass">"widget"
}

Response:

• Status: 200
• Body:

{
  class="text-pass">"orderId": class="text-pass">"order-123",
  class="text-pass">"status": class="text-pass">"completed",
  class="text-pass">"steps": {
    class="text-pass">"charge": { class="text-pass">"completed": true },
    class="text-pass">"reserve": { class="text-pass">"completed": true },
    class="text-pass">"confirm": { class="text-pass">"completed": true }
  }
}

Step Details

• charge: Records a payment charge for the given amount. Sets charge.completed = true.
• reserve: Reserves the item in inventory. Sets reserve.completed = true.
• confirm: Finalizes the order. Sets confirm.completed = true and overall status = "completed".

Each step should only execute if it hasn't been completed yet for this orderId.

Status Values

• "pending" — workflow has not started
• "charging" — charge step in progress
• "reserving" — reserve step in progress
• "confirming" — confirm step in progress
• "completed" — all steps done
• "failed" — a step failed (for future use)