Feature Request: Notification on model fallback

Feature Request

Summary
When the primary model fails and OpenClaw switches to a fallback model, send a notification to the user.

Use Case
Users want to know when they're getting responses from a fallback model instead of their primary model. This is important for:

• Awareness of service degradation
• Understanding response quality differences
• Debugging issues

Suggested Implementation
Options could include:

1. A configurable notification message when fallback is triggered
2. A hook that fires on model switch
3. A prefix/suffix added to responses from fallback models
4. Integration with existing notification channels (WhatsApp, Telegram, etc.)

Configuration Suggestion

{
  "agents": {
    "defaults": {
      "model": {
        "primary": "anthropic/claude-opus-4-5",
        "fallbacks": ["siliconflow/Qwen/Qwen3-Coder-480B-A35B-Instruct"],
        "notifyOnFallback": true,
        "fallbackNotificationMessage": "⚠️ Switched to fallback model: {model}"
      }
    }
  }
}

Environment

• OpenClaw version: 2026.2.9
• Primary use: WhatsApp channel

Thank you!