MessageOutputVersion

// v0 format - simple content representation
const v0Message: Message<{ outputVersion: "v0", content: ... }> = {
  type: "human",
  content: "Hello world" // string | Array<ContentBlock | ContentBlock.Text>
};

// v1 format - structured content blocks
const v1Message: Message<{ outputVersion: "v1", content: ... }> = {
  type: "human",
  content: [
    { type: "text", text: "Hello world" },
    { type: "image", image_url: "..." }
  ] // Array<ContentBlock | ...> (determined by the structure)
};