Unit tests for AgentSessionManager

[maxonary]

Issue

Critical realtime logic has no test coverage.

Current State

• No unit tests for voice functionality
• Hard to validate changes
• No regression prevention

Test Cases Needed

1. WebSocket Connection

   • Successful connection to gateway
   • Failed connection handling
   • Disconnection and recovery

2. Audio Handling

   • Audio buffer encoding to base64
   • Audio data sending over WebSocket
   • Invalid audio format handling

3. Message Handling

   • Parsing OpenAI realtime responses
   • Saving messages to ConversationStore
   • Error responses from OpenAI

4. State Management

   • isConnected state transitions
   • isListening state transitions
   • Error state updates

5. Main Actor Isolation

   • Verify all UI updates happen on main thread
   • No race conditions in state updates