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.