Nothing points the contributor at the next thing to do

Contributors have told us they reach a screen and don't know what to do next. The app knows — there's almost always one pending action for the current state — but it never points at it. The relevant control might be scrolled out of view, or sit among several panels with nothing to say "start here."

We want a way to draw attention to the next pending action: bring its block into view and mark it clearly enough that the next step is obvious, in a way that forgives a contributor who looks away or pauses to read.

Open questions

Is there always exactly one "next action," or does it depend on the site's state (fresh / mid-flow / done)? Working out which block to point at may be the larger half of this.
How does the cue clear — when the action is done, rather than on a fixed timer, so a distracted contributor doesn't lose their one hint.
Respect reduced-motion preferences for any movement or animation.

Related: the counterpart to this is telling the contributor what happened after they act — see #253.