Echo compares allowed origins literally, so "https://*" and "http://*" never matched a real origin and no CORS headers were sent. The allowed origins now come from CORS_ALLOWED_ORIGINS (comma-separated, checked at startup). When it is empty, only same-origin requests work, which is enough for the bundled frontend. Credentials are no longer allowed since the API uses Bearer tokens. Browsers may now send Range and X-Queue-Id and read X-Queue-Id and Content-Range.