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src/Notifier/StellaOps.Notifier/StellaOps.Notifier.Worker/Channels/WebhookChannelAdapter.cs

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+using System.Net.Http.Json;
+using System.Text.Json;
+using Microsoft.Extensions.Logging;
+using StellaOps.Notify.Models;
+
+namespace StellaOps.Notifier.Worker.Channels;
+
+/// <summary>
+/// Channel adapter for webhook (HTTP POST) delivery with retry support.
+/// </summary>
+public sealed class WebhookChannelAdapter : INotifyChannelAdapter
+{
+    private readonly HttpClient _httpClient;
+    private readonly ILogger<WebhookChannelAdapter> _logger;
+
+    public WebhookChannelAdapter(HttpClient httpClient, ILogger<WebhookChannelAdapter> logger)
+    {
+        _httpClient = httpClient ?? throw new ArgumentNullException(nameof(httpClient));
+        _logger = logger ?? throw new ArgumentNullException(nameof(logger));
+    }
+
+    public NotifyChannelType ChannelType => NotifyChannelType.Webhook;
+
+    public async Task<ChannelDispatchResult> SendAsync(
+        NotifyChannel channel,
+        NotifyDeliveryRendered rendered,
+        CancellationToken cancellationToken)
+    {
+        ArgumentNullException.ThrowIfNull(channel);
+        ArgumentNullException.ThrowIfNull(rendered);
+
+        var endpoint = channel.Config?.Endpoint;
+        if (string.IsNullOrWhiteSpace(endpoint))
+        {
+            return ChannelDispatchResult.Fail("Webhook endpoint not configured", shouldRetry: false);
+        }
+
+        if (!Uri.TryCreate(endpoint, UriKind.Absolute, out var uri))
+        {
+            return ChannelDispatchResult.Fail($"Invalid webhook endpoint: {endpoint}", shouldRetry: false);
+        }
+
+        var payload = new
+        {
+            channel = channel.ChannelId,
+            target = rendered.Target,
+            title = rendered.Title,
+            body = rendered.Body,
+            summary = rendered.Summary,
+            format = rendered.Format.ToString().ToLowerInvariant(),
+            locale = rendered.Locale,
+            timestamp = DateTimeOffset.UtcNow
+        };
+
+        try
+        {
+            using var request = new HttpRequestMessage(HttpMethod.Post, uri);
+            request.Content = JsonContent.Create(payload, options: new JsonSerializerOptions
+            {
+                PropertyNamingPolicy = JsonNamingPolicy.CamelCase
+            });
+
+            // Add HMAC signature header if secret is available (placeholder for KMS integration)
+            request.Headers.Add("X-StellaOps-Notifier", "1.0");
+
+            using var response = await _httpClient.SendAsync(request, cancellationToken).ConfigureAwait(false);
+            var statusCode = (int)response.StatusCode;
+
+            if (response.IsSuccessStatusCode)
+            {
+                _logger.LogInformation(
+                    "Webhook delivery to {Endpoint} succeeded with status {StatusCode}.",
+                    endpoint,
+                    statusCode);
+                return ChannelDispatchResult.Ok(statusCode);
+            }
+
+            var shouldRetry = statusCode >= 500 || statusCode == 429;
+            _logger.LogWarning(
+                "Webhook delivery to {Endpoint} failed with status {StatusCode}. Retry: {ShouldRetry}.",
+                endpoint,
+                statusCode,
+                shouldRetry);
+
+            return ChannelDispatchResult.Fail(
+                $"HTTP {statusCode}",
+                statusCode,
+                shouldRetry);
+        }
+        catch (HttpRequestException ex)
+        {
+            _logger.LogError(ex, "Webhook delivery to {Endpoint} failed with network error.", endpoint);
+            return ChannelDispatchResult.Fail(ex.Message, shouldRetry: true);
+        }
+        catch (TaskCanceledException) when (cancellationToken.IsCancellationRequested)
+        {
+            throw;
+        }
+        catch (TaskCanceledException ex)
+        {
+            _logger.LogWarning(ex, "Webhook delivery to {Endpoint} timed out.", endpoint);
+            return ChannelDispatchResult.Fail("Request timeout", shouldRetry: true);
+        }
+    }
+}