Retries and idempotency - Arena API

Safe to repeat

Every GET.
DELETE /api_keys/{id}. A second call answers 404 key_not_found: the key is already gone.

POST /api_keys is not idempotent: every call creates a new key.

When to retry

Response	Action
Network error or timeout	Retry with exponential backoff.
`429`	Wait `Retry-After` seconds (also `error.retryAfterSeconds`), then retry.
`500`, `503`	Retry with backoff. `503` carries `Retry-After`. The key may be fine.
Any other `4xx`	Final. Fix the request.

Polling

There is no streaming under a key. Records reads are cached for 30 seconds (Cache-Control: private, max-age=30), and leaderboards refresh daily at about 05:10 UTC (refreshedAt), so polling faster gains nothing and spends quota.