Replace the oscillation-prone IntersectionObserver/sentinel pattern with
a simpler always-sticky collapsible card. The card defaults to collapsed
(mini bar) and users toggle it manually. Outer scroll auto-collapses the
timeline to stay out of the way, with scroll-chaining prevention via
overscroll-behavior-y: contain.
Key changes:
- Remove sentinel, IntersectionObserver, and bidirectional isStuck state
- Always sticky at top-4 with unified info color scheme
- Manual toggle via clickable header with grid-rows animation
- Auto-collapse on outer scroll (one-way, prevents oscillation)
- Consolidate three task-end handlers into single handleTaskEnd
- Add hover interaction (muted-foreground → foreground)
- Add aria-expanded for accessibility
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
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