Add WebSocket Message Type

When to Use

• Adding a new command the control plane sends to agents
• Adding a new report/event agents send back to the control plane
• Extending the protocol for a new feature (sync, config, notifications, etc.)

Protocol Overview

WSMessage is a flat interface (not a discriminated union) — all messages share the same envelope:

{
  messageId: string;      // e.g. "memory-sync-1748700000000"
  type: WSMessageType;    // string literal from the union
  agentId?: string;       // sender's DID (set by the agent or control plane)
  payload: any;           // typed by convention via payload interface
  timestamp: string;      // ISO 8601
  signature?: string;     // ECDSA hex — only for critical messages
}

Procedure

1. Add the Type String to the Union

File: packages/shared/src/types.ts

Add your new type literal to the WSMessageType union:

export type WSMessageType =
  | ... existing types ...
  | "my_new_type";   // ← add here

2. Add the Payload Interface

In the same file (packages/shared/src/types.ts), add a typed payload interface:

export interface WSMyNewTypePayload {
  // required fields
  sourceId: string;
  // optional fields
  metadata?: Record<string, unknown>;
}

Naming convention: WS + PascalCase(type) + Payload (e.g. WSMemorySyncPayload).

3. Handle in the Control Plane (lib/ws-server.ts)

Direction: agent → control plane (agent sends, server receives):

Add a case to the switch (message.type) in handleMessage():

case "my_new_type":
  this.handleMyNewType(message);
  break;

Then implement the handler as a private method:

private handleMyNewType(message: WSMessage): void {
  const payload = message.payload as WSMyNewTypePayload;
  const agentId = message.agentId;
  // ... business logic ...
}

Direction: control plane → agent (server sends):

Add a public method to send the message:

sendMyNewTypeTo(agentDid: string, data: WSMyNewTypePayload): boolean {
  const agent = this.agents.get(agentDid);
  if (!agent || !agent.sender.isOpen()) return false;
  this.sendMessage(agent.sender, {
    messageId: `my-new-type-${Date.now()}`,
    type: "my_new_type",
    agentId: agentDid,
    payload: data,
    timestamp: new Date().toISOString(),
  });
  return true;
}

4. Handle in the Agent (src/agent.ts)

Add a case to the switch (message.type) in handleMessage():

case "my_new_type":
  this.handleMyNewType(message);
  break;

Implement the handler as a private method. Use .catch() for async:

private handleMyNewType(message: WSMessage): void {
  const payload = message.payload as WSMyNewTypePayload;
  // ... react to the message ...
}

// If async:
case "my_new_type":
  this.handleMyNewType(message).catch((e) => this.log("error", "handleMyNewType error", e));
  break;

For messages that agent sends to control plane, call this.send(message).

5. For Signed Messages (critical/policy-like)

Only if the message carries trust-sensitive data (policies, capability grants):

Signing (control plane side, before sending):

import { signMessage } from "@vaultysclaw/shared";

const payload = { ... };
const signature = await signMessage(JSON.stringify(payload), serverPrivateKey);
this.sendMessage(sender, { ..., payload, signature });

Verification (agent side, before processing):

import { verifySignature } from "@vaultysclaw/shared";

private async handleMySignedType(message: WSMessage): Promise<void> {
  const isValid = await verifySignature(
    JSON.stringify(message.payload),
    message.signature!,
    this.controlPlanePublicKey,
  );
  if (!isValid) {
    this.log("error", "Invalid signature — rejecting my_signed_type message");
    return;
  }
  // ... proceed ...
}

Add a status guard for post-auth messages (like intent, policy_update):

case "my_new_type":
  if (this._status !== "connected") {
    this.log("warn", "Received my_new_type before auth — ignoring");
    return;
  }
  this.handleMyNewType(message);
  break;

6. Checklist Before Done

• Type literal added to WSMessageType union in packages/shared/src/types.ts
• Payload interface added in packages/shared/src/types.ts (named WS<TypeName>Payload)
• packages/shared rebuilt (pnpm build -F @vaultysclaw/shared) before using in other packages
• case added to handleMessage() switch in lib/ws-server.ts
• Handler method implemented in ws-server.ts
• case added to handleMessage() switch in src/agent.ts
• Handler method implemented in agent.ts
• Signed messages: verification call before processing (agent side)
• Post-auth messages: _status !== "connected" guard in agent switch
• Async handlers wrapped with .catch() in agent switch