Feature: Webhook System for External Automation

[avikeid2007]

Summary

Add webhook support to the existing REST API server - send notifications to external URLs when events occur in KaiROS, and allow external systems to trigger actions.

Motivation

Connects KaiROS to external automation workflows (Zapier, IFTTT, n8n, Power Automate, custom scripts).

Detailed Requirements

Webhook Endpoints in ApiServer.cs

Add to the existing REST API:

• POST /api/webhooks - register a webhook (URL, events to subscribe, optional secret)
• DELETE /api/webhooks/{id} - remove a webhook
• GET /api/webhooks - list registered webhooks
• POST /api/webhooks/{id}/test - send a test payload

Supported Events

• chat.completed - fires when AI generates a complete response
• model.loaded - fires when a model is loaded
• model.unloaded - fires when a model is unloaded
• research.completed - fires when deep research finishes (if that feature exists)
• task.created - fires when a task is extracted from chat (if that feature exists)

Webhook Payload Format

{
    "event": "chat.completed",
    "timestamp": "2026-06-26T09:00:00Z",
    "data": {
        "session_id": "abc-123",
        "model": "qwen-3.5-9b",
        "user_message": "What is recursion?",
        "assistant_message": "Recursion is...",
        "token_count": 150
    },
    "signature": "sha256=..."
}

Implementation: WebhookService.cs

public interface IWebhookService
{
    Task RegisterAsync(WebhookRegistration registration);
    Task UnregisterAsync(string id);
    Task<List<WebhookRegistration>> GetAllAsync();
    Task FireEventAsync(string eventName, object data);
}

• Store webhook registrations in SQLite
• On event trigger, POST JSON payload to registered URLs
• Include HMAC-SHA256 signature header for verification
• Retry logic: 3 attempts with exponential backoff (1s, 5s, 25s)
• Log delivery status (success/failure) for debugging

Database (DatabaseService.cs)

Add Webhooks table: Id, Url, Events (comma-separated), Secret, CreatedAt, IsActive.

Files to Create/Modify

• [NEW] Services/WebhookService.cs + IWebhookService.cs
• [NEW] Models/WebhookModels.cs
• [MODIFY] Services/ApiServer.cs - add webhook CRUD endpoints
• [MODIFY] Services/DatabaseService.cs - add Webhooks table
• [MODIFY] ViewModels/ChatViewModel.cs - fire chat.completed event

Acceptance Criteria

• Register/unregister webhooks via REST API
• Webhooks fire on supported events with correct payload
• HMAC-SHA256 signature included in headers
• Retry logic for failed deliveries (3 attempts)
• Test endpoint sends a sample payload