Function buildSubagentTree

ui-tui/src/lib/subagentTree.ts:17–48

(items: readonly SubagentProgress[])

 * and the tree renders flat — matching pre-observability behaviour.
 */
export function buildSubagentTree(items: readonly SubagentProgress[]): SubagentNode[] {
  if (!items.length) {
    return []
  }

  const byParent = new Map<string, SubagentProgress[]>()
  const known = new Set<string>()

  for (const item of items) {
    known.add(item.id)
  }

  for (const item of items) {
    const parentKey = item.parentId && known.has(item.parentId) ? item.parentId : ROOT_KEY
    const bucket = byParent.get(parentKey) ?? []
    bucket.push(item)
    byParent.set(parentKey, bucket)
  }

  for (const bucket of byParent.values()) {
    bucket.sort((a, b) => a.depth - b.depth || a.index - b.index)
  }

  const build = (item: SubagentProgress): SubagentNode => {
    const kids = byParent.get(item.id) ?? []
    const children = kids.map(build)

    return { aggregate: aggregate(item, children), children, item }
  }

  return (byParent.get(ROOT_KEY) ?? []).map(build)
}

/**
 * Roll up counts for a node's whole subtree.  Kept pure so the live view