companion

Companion creative shown alongside this asset — the second box of a double break, and the backdrop of an lshape_ad. Mirrors the web AssetWithCompanion.companion.

Until this existed the Kotlin model had no companion at all (its own doc comment deferred it to "the player phase"), so a double break reached the renderer with nothing to put in the second box and drew a single fullscreen ad instead — while still reporting format=double on every event, so the e2e suite passed on a visibly wrong render.

Typed as a nested Asset rather than a distinct class so a companion can itself carry uri/mediaType/duration exactly like a primary asset, matching web.