Honor prefers-reduced-motion

Some users experience motion sickness or vestibular symptoms from movement they did not initiate. The media query surfaces an OS-level preference they have already expressed, so honouring it costs one @media block. The load-bearing detail: "reduced" is not "none". Strip the spatial travel and the spring, but KEEP the opacity crossfades and the instant state changes, so the interface still says what happened — a state change that was only ever communicated by motion becomes invisible the moment the motion is dropped (animations-lottie-never-opacity-only is the corollary). ibelick's baseline-ui converges on the same rule from the agent-guidelines side ("SHOULD respect `prefers-reduced-motion`"), which is why this corpus states it once here rather than twice.

CAVEAT, and it is worth stating plainly: Raphael Salaja's sounds-on-the-web skill advises treating prefers-reduced-motion as a proxy for sound sensitivity — defaulting audio OFF when it is set. That is pragmatic, because no `prefers-reduced-sound` media query has ever shipped, and it is a defensible default. But it is lossy: a vestibular preference is not a sound preference, and the overlap is a guess, not a signal.

Use it as a default-OFF heuristic, never as a substitute for an explicit, persisted sound toggle (see interactions-sound-is-user-owned).