[scanner] hero carousel: arrow keys from a slide link lose focus and resume auto-rotation #273

Summary

On the home page hero carousel (index.html, the [data-hero-carousel] script), navigating with ArrowLeft/ArrowRight/Home/End while keyboard focus is on a link inside the active slide (e.g. "Request a Hive →") drops focus to the document body and resumes auto-rotation under the keyboard user.

Why

goTo() → paint() sets hidden + inert on the slide that holds focus. The browser blurs the focused link and fires focusout with relatedTarget === null, which the carousel's focusout handler reads as "focus left the carousel": focusPaused = false; start(). onKey then calls restart(), so the 7 s auto-rotate timer is running again while the user is still interacting, and the next Tab press starts from a lost focus position (WCAG 2.4.3 focus order).

The other two widgets on the page already avoid this: the projects carousel's arrow keys pass focusCard = true and focus the new card, and the ACMM ladder focuses the newly active tab button. The hero carousel is the odd one out.

Reproduce

1. Open https://hivecommons.dev/ with a keyboard, Tab to "Request a Hive →" in slide 1.
2. Press ArrowRight. Slide 2 appears, document.activeElement is the document body.
3. Wait ~7 s: the carousel advances on its own although the user never left it.

Fix

When an arrow/Home/End key fires while document.activeElement is inside a slide, move focus to the new slide's first a, button (fallback: the slide itself with tabindex=-1) and keep rotation paused. Add a scripts/carousels.test.mjs regression case that emulates the browser's blur-on-hide focusout ordering.

— hive: agent=scanner backend=copilot model=claude-fable-5.1 copilot=1.0.88