feat(messages): Add typed EventEmitter generics for NDKMessenger and NDKConversation

[cardugarte]

Summary

NDKMessenger and NDKConversation both extend EventEmitter from eventemitter3 without type parameters, making all .on(), .off(), and .emit() calls untyped. This means consumers can't get compile-time safety for event names or callback signatures.

Additionally, there's a minor bug in handleIncomingMessage where conversation-created is emitted on every incoming message instead of only on the first message of a new conversation.

Problem

1. Untyped EventEmitter

// Current (src/messenger.ts)
class NDKMessenger extends EventEmitter { ... }

// Consumer gets no type safety:
messenger.on('mesage', (msg) => { ... })  // typo, no error
messenger.on('message', (msg: string) => { ... })  // wrong type, no error

eventemitter3 supports a type map generic that would solve this:

interface NDKMessengerEvents {
  'message': (message: NDKMessage) => void;
  'conversation-created': (conversation: NDKConversation) => void;
  'error': (error: ErrorEvent) => void;
}

class NDKMessenger extends EventEmitter<NDKMessengerEvents> { ... }

Same for NDKConversation:

interface NDKConversationEvents {
  'message': (message: NDKMessage) => void;
  'error': (error: ErrorEvent) => void;
  'state-change': (event: StateChangeEvent) => void;
}

class NDKConversation extends EventEmitter<NDKConversationEvents> { ... }

2. Bug in conversation-created emission

In src/messenger.ts, handleIncomingMessage:

// Current (line ~840)
if (conversation.getMessages.length === 1) {
  this.emit("conversation-created", conversation);
}

conversation.getMessages.length reads the function arity (number of parameters of getMessages, which is always 1 because of the limit? param), not the message count. This means conversation-created fires on every incoming message.

Suggested fix:

const messages = await conversation.getMessages();
if (messages.length === 1) {
  this.emit("conversation-created", conversation);
}

Workaround

We're currently using module augmentation in our project to add type safety locally:

// messenger-events.d.ts
declare module '@nostr-dev-kit/messages' {
  interface NDKMessengerEvents { ... }
  interface NDKConversationEvents { ... }
  // augment classes to use typed generics
}

Offer

If you agree with these changes, I'd be happy to submit a PR addressing both issues. The scope would be:

1. Add event type interfaces (NDKMessengerEvents, NDKConversationEvents)
2. Apply them as generics to EventEmitter<T>
3. Fix the conversation-created emission logic
4. Export the event interfaces for consumers

Let me know!