[AI] Fix crash caused by unhandled goAway server message in LiveSession

[Kick-snare]

Description

Fixes #7648

This PR adds support for the goAway server message type in LiveSession to prevent crashes when the server initiates a disconnect. Previously, when the server sent a goAway message, the app would crash with a SerializationException because the message type was not recognized by LiveServerMessageSerializer.

Changes

1. Add LiveServerGoAway message type

• Added LiveServerGoAway class to represent server-initiated disconnection
• Includes timeLeft: String? field containing duration in protobuf format (e.g., "57s", "1.5s")
• Added parseTimeLeft() helper method to convert timeLeft string to kotlin.time.Duration
• Registered goAway message in LiveServerMessageSerializer

2. Robust Handling & API Update

• Crash Prevention: Added CoroutineExceptionHandler to networkScope and audioScope to act as a safety net against unhandled exceptions.
• Graceful Shutdown: Implemented logic in processModelResponses() to recognize GoAway signals and automatically close the session, preventing zombie connections or further crashes.
• Public API: Added goAwayHandler to LiveAudioConversationConfig.
  • Rationale: While internal handling prevents the crash, apps often need to inform the user that the session ended due to server maintenance or timeouts. This handler exposes the timeLeft information to the application layer.

3. Comprehensive unit tests

• Created LiveServerMessageTests.kt with 18 test cases covering:
  • Duration parsing (integer seconds, fractional seconds, edge cases)
  • LiveServerGoAway deserialization (with/without timeLeft)
  • Polymorphic serializer recognition
• Added serialization schema test in SerializationTests.kt
• All 164 tests pass

Usage Example

Apps can now handle server disconnections gracefully using the goAwayHandler:

val config = LiveAudioConversationConfig.Builder()
  .setGoAwayHandler { goAway ->
    val timeLeft = goAway.parseTimeLeft()
    Log.i(TAG, "Server disconnecting in ${timeLeft?.inWholeSeconds} seconds")
    // Clean up resources, show UI notification, etc.
  }
  .build()

liveGenerativeModel.startAudioConversation(config)

Testing

• ✅ All 164 unit tests pass
• ✅ Tested with real app and confirmed graceful handling of goAway messages (Published to local Maven)
• ✅ Spotless formatting applied

Related Issues

• Android SDK: SerializationException on "goAway" message in LiveSession #7648
• Flutter SDK: 🚀 [firebase_ai] Support GoAway message in LiveGenerativeModel flutterfire#17836

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