A presentation-only navigation + expansion surface for deeply nested discussions — expand/collapse branches, jump to next unread branch, go-to-parent, selected-path breadcrumb, collapse-resolved, deleted-reply placeholder, and lazy reply loading (loading/error/retry/load-more). Rendered as an accessible tree; depth-capped so pathological threads never render unbounded. Distinct from Comment Thread.
pnpm dlx shadcn@latest add "https://motiq.dev/r/thread-expansion.json"