Re-direct an avatar's resting loop

Re-direct the avatar's RESTING LOOP — the video she plays when nothing else is happening — from a new one-sentence description. Not a clip: a clip with role "idle" is a variant spliced OVER the loop, and declaring one never changes what she rests in. 202; the render takes minutes, during which she stays ready and keeps serving her previous loop (returned as servingUrl), and the swap publishes atomically once the new loop is usable. The clip library is untouched. Billed as one generation at the rendering model's rate. Needs a portrait to re-animate: 422 loop_not_generatable (terminal) on a grandfathered avatar built from a supplied video with no portrait — the gate is the portrait, not sourceKind, which reads "video" on every avatar once its generated loop has attached. Supports Idempotency-Key replay — send one on retries, because a repeated re-direct is a second billed render.

Requires an API key with the avatars:write scope.