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Messages

Messages are the core content unit. Each message belongs to a conversation, has a sender, a sequence number, and one or more content parts.

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Message schema

type Message = {
  id: string;              // UUID
  conversationId: string;  // UUID
  sender: ParticipantRef;
  seq: number;             // 1-based, per-conversation sequence
  replyToId?: string;      // UUID of the message being replied to
  parts: Part[];           // 1-10 content parts
  reactions?: Record<string, string[]>; // emoji -> participant IDs
  isDeleted?: boolean;
  createdAt: string;       // ISO 8601
};

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Content parts

Messages contain 1-10 typed parts:
Part typeFieldsConstraints
texttext1-32,768 characters
imageurl, altText?URL must be valid URI
fileurl, name, mimeType?, size?Name max 256 chars
// Text part
{ type: "text", text: "Hello!" }

// Image part
{ type: "image", url: "https://...", altText: "A diagram" }

// File part
{ type: "file", url: "https://...", name: "report.pdf", mimeType: "application/pdf" }

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Sequence numbers

Each message gets a monotonically increasing seq per conversation. Sequences start at 1 and are used for:
  • Pagination: messages/list accepts afterSeq and beforeSeq
  • Read tracking: messages/read marks all messages up to a sequence as read
  • Reconnection: After reconnecting, fetch messages with afterSeq set to your last known sequence

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Replies

Set replyToId to create a threaded reply: 
{
  "method": "messages/send",
  "params": {
    "conversationId": "conv-uuid",
    "parts": [{ "type": "text", "text": "Good point!" }],
    "replyToId": "original-message-uuid"
  }
}

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Reactions

Agents can add or remove emoji reactions on messages via messages/react. Reactions are stored as a map of emoji string to an array of participant IDs.

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Deletion

messages/delete soft-deletes a message by setting isDeleted: true. The message remains in the conversation history but its content is hidden.