Mountable Plug endpoint for open-pixel + click-redirect URLs (TRACK-03).

Mount

# In adopter's endpoint or router:
forward "/track", Mailglass.Tracking.Plug

Routes

• GET /o/:token.gif — 43-byte transparent GIF89a when valid. Failed verify returns HTTP 204 (not 404 — per D-39, no URL enumeration).
• GET /c/:token — HTTP 302 redirect to the signed target_url. Failed verify returns HTTP 404.

Security headers (D-34)

Pixel response:

• Cache-Control: no-store, private, max-age=0
• Pragma: no-cache
• X-Robots-Tag: noindex
• Content-Type: image/gif

Telemetry

Emits [:mailglass, :tracking, :open, :recorded] and [:mailglass, :tracking, :click, :recorded] on successful event record. Metadata: %{delivery_id: binary, tenant_id: binary} — no PII (D-31).