Add availableCommands to New Session

[yordis]

Following the slash commands spec, I implemented this:

async newSession(params: NewSessionRequest): Promise<NewSessionResponse> {
  // Create session internally
  const session = await this.sessionManager.createSession({ 
    cwd: params.cwd, 
    mcpServers: params.mcpServers 
  });
  
  // Send notification (as spec says: "after creating a session")
  await this.connection.sessionUpdate({
    sessionId: session.id,
    update: {
      sessionUpdate: 'available_commands_update',
      availableCommands: getAvailableCommands()
    }
  });
  
  // Return response
  return {
    sessionId: session.id,
    modes: { ... }
  };
}

What Went Wrong

The notification arrived BEFORE the response:

1. Client → Server: session/new request
2. Server → Client: available_commands_update notification ❌
3. Server → Client: session/new response

Zed editor:

Time 2: Receives notification
        → Tries to store commands for session
        → Session doesn't exist yet in client state!
        → Error: "Failed to get session"
        → Commands discarded

Time 3: Receives response
        → Creates session
        → But commands already discarded!

Result: Slash commands never appeared in the UI.

---

My Fix

Using setImmediate() to defer the notification until after the response is sent:

async newSession(params: NewSessionRequest): Promise<NewSessionResponse> {
  const session = await this.sessionManager.createSession({ 
    cwd: params.cwd, 
    mcpServers: params.mcpServers 
  });
  
  const response = {
    sessionId: session.id,
    modes: { ... }
  };
  
  // Defer notification until AFTER response is sent
  setImmediate(async () => {
    await this.connection.sessionUpdate({
      sessionId: session.id,
      update: {
        sessionUpdate: 'available_commands_update',
        availableCommands: getAvailableCommands()
      }
    });
  });
  
  return response; // Response sent immediately
}

Now the order is correct. But this is very confusing, and it feels like a hack.

---

I feel that we should send the availableCommands as part of session/new

// session/new
{
  "sessionId": "26250dbc-9e5f-40e5-90d8-5304b0d75428",
  "modes": {
    "currentModeId": "chat",
    "availableModes": [
      {
        "id": "review",
        "name": "Review",
        "description": "Analyze code and provide detailed suggestions for improvement"
      }
    ],
    "availableCommands": [
      {
        "name": "fix",
        "description": "Find and fix issues in code",
        "input": {
          "hint": "description of the issue"
        }
      }
    ]
  }
}

[benbrandt]

hi, the reason for this is that for many clients, available commands can also include loading a bunch of files within the project, which can take some amount of time.
It could be nice to return some built-in ones first and then provide a different list later, but I think we'd always want this session update because the agent may want to update it's list of available commands.

Adding this to session new would also be a breaking change in a sense because clients that don't know about the field wouldn't read it, and then they also wouldn't receive a list of commands later if the notification wasn't sent.

We can revisit for a v2 change.

[yordis]

I definitely see the need for async updating the list of commands.

In the meantime, is it a good idea to add some documentation around dealing with the timing issue?