Add onAgentToolRequest callback for webhook tool call notifications

[AdnanKhan45]

The ElevenLabs WebSocket protocol sends agent_tool_request events when the agent initiates a webhook/server tool call. The Android SDK already handles this event (fixed in elevenlabs-android PR #34, released in v0.7.1).

The Flutter SDK does not parse agent_tool_request events. The onDebug callback does not emit them either, suggesting they are dropped during WebSocket message parsing.

Impact: When the agent calls a webhook tool (e.g., fetching data from a backend), the Flutter client cannot distinguish between "agent is waiting for user to speak" and "agent is executing a tool call." Both appear as ConversationMode.listening with silence. This makes it impossible to show a loading/thinking indicator during tool execution.

Expected: Add onAgentToolRequest callback to ConversationCallbacks, matching the Android SDK's behavior:

ConversationCallbacks(
  onAgentToolRequest: ({required String toolName, required String toolCallId}) {
    // Tool call started — show thinking indicator
  },
  onAgentToolResponse: (AgentToolResponse response) {
    // Tool call completed — hide thinking indicator (already exists)
  },
)

Environment:

Package: elevenlabs_agents (Flutter)
Tested on iOS
The agent_tool_request event is confirmed to be part of the WebSocket protocol (handled by Android SDK since v0.7.1)

[PaulAsjes]

Thanks, we'll get on this.

[PaulAsjes]

Fixed in version 0.4.0!