CC-11: Add a sticky sidebar widget to long-form guides

  • Source document: .agents/core-content-promotion-plan.md (§4.1 “Contextual sidebars”)
  • Owner: 🤖 Agent
  • Priority: Low–Medium
  • Status: Not started. _layouts/post.html is a single centred column with no sidebar.
  • Depends on: A post-to-pathway mapping (see CC-06 / CC-02 _data/pathways.yml)

Task

On long-form guides, show a sticky sidebar (desktop) linking to the related pathway’s pillar content. On smaller screens, show it as an inline block.

Context

  • Only enable it for long posts: an opt-in front-matter flag (sidebar: true), or a word-count threshold calculated as in _includes/read_time.html.
  • Desktop: position: sticky in a col-lg-3 next to a col-lg-8 article. Don’t hurt reading width. Mobile: show it after the intro or at the end, never as an overlay.
  • Content: pathway name, three to five pillar links, and an optional drill pack mini-CTA.
  • Must not cause CLS or overlap the fixed navbar (#mainNav).

Completion criteria

  • Sidebar appears on eligible long-form guides, sticky on desktop and inline on mobile.
  • Links point to the right pathway’s pillar posts.
  • Lighthouse accessibility and performance ≥ 90 on a sample guide.
  • bundle exec jekyll build completes without errors.