Record a teaser event sent by the widget beacon. Params: c (creative_id), z (zone), s (site_key), t (optional event type). Whitelisted video types follow the established convention: v_start / v_q25 / v_q50 / v_q75 / v_complete / v_close ('video_start' is accepted as a legacy alias and stored as v_start).

Anything else is stored as w_click, NOT click. The widget fires this beacon on the same click that navigates to /go, and /go records the canonical click with its full dimensions (country, device, os, browser). Storing both as 'click' counted every widget click twice and inflated CR. w_click stays as the widget- side witness: w_clicks minus clicks is the tracking loss.

Returns a 1x1 GIF for the img fallback. events.event_type is free TEXT - new types need no migration.