Function createMuxMessage

src/common/types/message.ts:889–915

(
  id: string,
  role: "user" | "assistant",
  content: string,
  metadata?: MuxMetadata,
  additionalParts?: MuxMessage["parts"]
)

// Helper to create a simple text message
export function createMuxMessage(
  id: string,
  role: "user" | "assistant",
  content: string,
  metadata?: MuxMetadata,
  additionalParts?: MuxMessage["parts"]
): MuxMessage {
  const textPart = content
    ? [{ type: "text" as const, text: content, state: "done" as const }]
    : [];
  const parts = [...textPart, ...(additionalParts ?? [])];

  // Validation: User messages must have at least one part with content
  // This prevents empty user messages from being created (defense-in-depth)
  if (role === "user" && parts.length === 0) {
    throw new Error(
      "Cannot create user message with no parts. Empty messages should be rejected upstream."
    );
  }

  return {
    id,
    role,
    metadata,
    parts,
  };
}