Function findRootNodes

packages/cli/src/commands/dag.ts:238–256

* Find root nodes (nodes with no incoming edges). * Returns nodes sorted by their order in the DAG. * If no roots exist (cycle-only graph), returns all nodes to ensure rendering.

(dag: BlockDependencyDag)

 * If no roots exist (cycle-only graph), returns all nodes to ensure rendering.
 */
function findRootNodes(dag: BlockDependencyDag): string[] {
  const hasIncoming = new Set<string>()
  for (const edge of dag.edges) {
    hasIncoming.add(edge.to)
  }

  let roots = dag.nodes.filter(node => !hasIncoming.has(node.id)).map(node => node.id)

  // If no roots found (cycle-only graph), use all nodes as roots
  if (roots.length === 0) {
    roots = dag.nodes.map(node => node.id)
  }

  // Sort by order
  const nodeMap = buildNodeMap(dag)
  roots.sort((a, b) => (nodeMap.get(a)?.order ?? 0) - (nodeMap.get(b)?.order ?? 0))

  return roots
}

/**
 * Build sorted children for a node, deduplicating edges to the same child.