Root cause: OSStatus 561145187 - AVAudioSession was not in
.playAndRecord + .voiceChat mode when VoiceProcessingIO tried to start.
Two changes:
1. Activate session BEFORE rust.connect() so it is ready when auto-join runs
2. Defensive activation in Connected handler as backup (idempotent)
This fixes both the audio error and the subsequent voice_in already taken
error that occurred after auto-join consumed voice_in on failure.