Email-open tracking pixel. Looks up a sent campaign email request by unique_code and, on first view, stamps opened_at (and delivered_at if unset). Returns an image/png response so it can be embedded as an <img> in the email body — not a JSON envelope on the happy path.

Path params

Auth

• Public — no bearer token (unauthenticated campaign group; item marked noauth). Requested by the recipient's mail client when the email is opened.

Rate limit

• 30 requests/min per IP (public).

Behaviour

• 200 with Content-Type: image/png (tracking pixel) on success; caching disabled via Cache-Control/Pragma/Expires headers.
• 200 JSON { status: "failed", message: "Sent email not found" } when no matching sent email request exists.
• 200 JSON { status: "failed", message: "Something went wrong! Please try again." } on unexpected error (still 200, so the mail client renders nothing broken).