# Idempotency

Idempotency guarantees that repeating the **same** write request (POST, PUT, PATCH) within a short window returns the original response instead of creating a duplicate object. Bead will add this feature soon; the details below describe the planned contract so you can design for it now.

### Status

Idempotency is **not yet enforced** in Sandbox or Production. Expect network retries to create duplicate records until enforcement is announced in the changelog.

### Header format

| Header          | Example value                          | Notes                            |
| --------------- | -------------------------------------- | -------------------------------- |
| Idempotency-Key | `550e8400-e29b-41d4-a716-446655440000` | Case-insensitive UUID v4 string. |

### Evaluation rules (planned)

| Condition                                                     | Server behaviour                                               |
| ------------------------------------------------------------- | -------------------------------------------------------------- |
| Same `Idempotency-Key` and identical request body within 24 h | Return the cached 2xx response (status and body).              |
| Same `Idempotency-Key` but different body                     | Return **409 Conflict** with an error explaining the mismatch. |
| Key older than 24 h                                           | Treat as a brand-new request.                                  |

Keys are stored per endpoint path; using the same key for different paths does not collide.

### Example

```bash
curl -X POST "$BEAD_API/Locations" \
     -H "Authorization: Bearer $TOKEN" \
     -H "Idempotency-Key: 550e8400-e29b-41d4-a716-446655440000" \
     -H "Content-Type: application/json" \
     -d '{ "merchantId": "mer_123", "address": {...} }'
```

If the client times out and sends the identical call again with the same key, the API responds with the original **201** body.

### Best practices

* Generate a fresh UUID v4 for each logical operation (one per new location, one per new terminal, etc.).
* Store the key client-side until the operation succeeds or fails definitively.
* Do not reuse keys across resource types or different merchants.
* If you receive **409 Conflict**, inspect the error; it means the same key was used with a modified body.
* Maintain client-side retries with exponential back-off even after idempotency is live; the feature only prevents duplication, it does not guarantee success.

### Go-live checklist for integrators

1. Implement the header now in sandbox calls; it will be ignored until launch.
2. Log any **409 Conflict** responses so you can catch accidental key reuse.
3. Watch the global changelog for the announcement that enforcement is active.


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