add LoopbackInsinTelemetry with rate-limited warn logging

Inspectron.Epson/PrintServer/Telemetry/LoopbackInsinTelemetry.cs

@@ -0,0 +1,56 @@
+using System.Net.Http.Json;
+using Microsoft.Extensions.Logging;
+
+namespace Inspectron.Epson.PrintServer.Telemetry;
+
+public sealed class LoopbackInsinTelemetry : IInsinTelemetry
+{
+    private const string Endpoint = "http://127.0.0.1:47823/events";
+    private static readonly TimeSpan RequestTimeout = TimeSpan.FromSeconds(2);
+    private static readonly long WarnIntervalTicks = TimeSpan.FromMinutes(5).Ticks / TimeSpan.TicksPerMillisecond;
+
+    private readonly HttpClient _http;
+    private readonly ILogger _logger;
+    private long _lastWarnMs = -WarnIntervalTicks;
+
+    public LoopbackInsinTelemetry(HttpClient http, ILogger logger)
+    {
+        _http = http;
+        _logger = logger;
+    }
+
+    public void Emit(string kind, string message)
+    {
+        var payload = new
+        {
+            kind,
+            message,
+            at = DateTime.UtcNow.ToString("yyyy-MM-ddTHH:mm:ss.fffZ")
+        };
+        _ = Task.Run(() => SendAsync(payload));
+    }
+
+    private async Task SendAsync(object payload)
+    {
+        try
+        {
+            using var cts = new CancellationTokenSource(RequestTimeout);
+            using var resp = await _http.PostAsJsonAsync(Endpoint, payload, cts.Token);
+            if (!resp.IsSuccessStatusCode)
+                MaybeWarn($"insin loopback returned {(int)resp.StatusCode}");
+        }
+        catch (Exception ex)
+        {
+            MaybeWarn($"insin loopback unreachable at 127.0.0.1:47823 ({ex.GetType().Name}), dropping events");
+        }
+    }
+
+    private void MaybeWarn(string message)
+    {
+        var now = Environment.TickCount64;
+        var last = Interlocked.Read(ref _lastWarnMs);
+        if (now - last < WarnIntervalTicks) return;
+        if (Interlocked.CompareExchange(ref _lastWarnMs, now, last) != last) return;
+        _logger.LogWarning("{Message}", message);
+    }
+}