set_asset_poster

Link an uploaded 640px WebP/JPEG to the shared video poster cache; clears failed-capture cooldowns.

Link an ordinary uploaded WebP/JPEG image (max 640px, 512KiB) to a stored video. Uses the immutable per-video preview cache across every tab and clears failed-capture cooldown. Upload the image once via create_asset_uploads; give videoId and posterId from the same board. Requires board write access.