Auth keys
Allow-list of `DeepL-Auth-Key` values (the full key string — a Free-plan `:fx` suffix is part of it). Anything else gets the documented 403.
Fault injection
Injected latency (ms) before every call; force-failure 429 / 456 / 500 / 503 answer with their documented `{message}` bodies until cleared.
Recent translations
Every translated item: source text, target, whether `context` was sent (result carries the `|ctx` marker), and the returned text. Usage counter feeds /v2/usage.
Requests from the backend
Danger zone
wipes payments, logs and every runtime override — back to configured defaults