ui/message content format discrepancy: SEP-1865 specifies object

The @modelcontextprotocol/ext-apps SDK sends ui/message with content as an array, but SEP-1865 specifies it as a single object.

From SEP

  // ui/message request
  {
    jsonrpc: "2.0",
    id: 2,
    method: "ui/message",
    params: {
      role: "user",
      content: {
        type: "text",
        text: string
      }
    }
  }

SDK Behavior

  {
    jsonrpc: "2.0",
    id: 2,
    method: "ui/message",
    params: {
      role: "user",
      content: [{ type: "text", text: "..." }]  // Array, not object
    }
  }

Hosts implementing strictly per SEP-1865 will fail to extract text from SDK-generated ui/message requests.

Start by comparing the SDK's ui/message request generation with the SEP-1865 example linked in the issue. Trace where the content value is assembled and verify the resulting request shape. Done means SDK-generated requests use the single text object specified by SEP-1865 and strict hosts can extract the text.