feat: add dagre layout utility for React Flow node positioning

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/lib/dagreLayout.ts

@@ -0,0 +1,44 @@
+import dagre from '@dagrejs/dagre'
+import type { Node, Edge } from '@xyflow/react'
+
+const NODE_WIDTH = 280
+const DEFAULT_NODE_HEIGHT = 100
+
+interface LayoutOptions {
+  direction?: 'TB' | 'LR'
+  rankSep?: number
+  nodeSep?: number
+}
+
+export function getLayoutedElements(
+  nodes: Node[],
+  edges: Edge[],
+  options: LayoutOptions = {}
+): Node[] {
+  const { direction = 'TB', rankSep = 100, nodeSep = 40 } = options
+
+  const g = new dagre.graphlib.Graph()
+  g.setDefaultEdgeLabel(() => ({}))
+  g.setGraph({ rankdir: direction, ranksep: rankSep, nodesep: nodeSep })
+
+  nodes.forEach((node) => {
+    const height = node.measured?.height ?? node.data?.estimatedHeight ?? DEFAULT_NODE_HEIGHT
+    g.setNode(node.id, { width: NODE_WIDTH, height })
+  })
+
+  edges.forEach((edge) => {
+    g.setEdge(edge.source, edge.target)
+  })
+
+  dagre.layout(g)
+
+  return nodes.map((node) => {
+    const dagreNode = g.node(node.id)
+    // dagre gives center positions — convert to top-left for React Flow
+    const x = dagreNode.x - NODE_WIDTH / 2
+    const y = dagreNode.y - (dagreNode.height ?? DEFAULT_NODE_HEIGHT) / 2
+    return { ...node, position: { x, y } }
+  })
+}
+
+export { NODE_WIDTH, DEFAULT_NODE_HEIGHT }