Marketplace flow

{
  "nodes": [
    { "id":"b","type":"ellipse","label":"Buyer","x":40,"y":160,"fill":"#dbeafe","stroke":"#2563eb" },
    { "id":"m","type":"rect","label":"Marketplace","x":260,"y":160,"fill":"#ede9fe","stroke":"#6d28d9" },
    { "id":"s","type":"ellipse","label":"Seller","x":480,"y":160,"fill":"#dbeafe","stroke":"#2563eb" },
    { "id":"es","type":"rect","label":"Escrow","x":260,"y":300,"fill":"#fef3c7","stroke":"#a16207" },
    { "id":"sh","type":"rect","label":"Ship","x":480,"y":300,"fill":"#fed7aa","stroke":"#c2410c" },
    { "id":"rv","type":"rect","label":"Review","x":700,"y":160,"fill":"#dcfce7","stroke":"#15803d" }
  ],
  "edges": [
    { "id":"a","source":"b","target":"m","label":"browse / pay" },
    { "id":"b","source":"m","target":"es","label":"hold funds" },
    { "id":"c","source":"m","target":"s","label":"notify" },
    { "id":"d","source":"s","target":"sh" },
    { "id":"e","source":"sh","target":"b","label":"deliver" },
    { "id":"f","source":"b","target":"rv" },
    { "id":"g","source":"es","target":"s","label":"release funds" }
  ]
}