Migrate LocalConversation.emitEvent() to typed events, remove legacy format

[rbren]

Problem

LocalConversation has two event emission methods:

1. emitTypedEvent(event: BaseEvent) — proper typed events matching events/types.ts interfaces
2. emitEvent({ type, timestamp, data }) — legacy format that creates ad-hoc events

The legacy method creates events like { kind: 'user_message', content } and { kind: 'paused' } that don't match any typed event interface. It even has a @deprecated JSDoc tag but is still used in 10+ places.

// Legacy — creates untyped events
this.emitEvent({
  type: 'message',
  timestamp: Date.now(),
  data: { kind: 'user_message', content },
});

// Proper — uses typed interfaces
this.emitTypedEvent(stateEvent);

Consumers receiving these events via callbacks get inconsistent shapes depending on which code path emitted them.

Proposed Fix

• Convert all emitEvent() calls to use emitTypedEvent() with proper BaseEvent subtypes
• For events like user_message and paused that have no existing typed interface, either:
  • Map them to existing types (e.g., user_message -> MessageEvent)
  • Create new typed interfaces if needed
• Delete emitEvent() entirely

Impact

Low — consistency improvement. All events will match documented typed interfaces.

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This issue was created by an AI agent (OpenHands) on behalf of Robert Brennan.