Add desktop lifecycle shutdown endpoints

Adds local-only desktop API endpoints and browser lifecycle script support so the app can schedule or cancel shutdown when the browser session ends.

Controllers/DesktopController.cs

@@ -0,0 +1,72 @@
+using System.Net;
+using AVSCartonShipmentVerifier.Configuration;
+using AVSCartonShipmentVerifier.Hosting;
+using Microsoft.AspNetCore.Mvc;
+using Microsoft.Extensions.Options;
+
+namespace AVSCartonShipmentVerifier.Controllers;
+
+[ApiController]
+[Route("api/desktop")]
+public sealed class DesktopController : ControllerBase
+{
+    private readonly DesktopShutdownService _shutdown;
+    private readonly IOptions<DesktopHostOptions> _options;
+
+    public DesktopController(DesktopShutdownService shutdown, IOptions<DesktopHostOptions> options)
+    {
+        _shutdown = shutdown;
+        _options = options;
+    }
+
+    [HttpPost("register-session")]
+    public IActionResult RegisterSession()
+    {
+        if (!IsShutdownEnabled() || !IsLocalRequest())
+        {
+            return NotFound();
+        }
+
+        _shutdown.MarkDashboardSessionActive();
+        _shutdown.CancelScheduledShutdown();
+        return Ok();
+    }
+
+    [HttpPost("schedule-shutdown")]
+    public IActionResult ScheduleShutdown()
+    {
+        if (!IsShutdownEnabled() || !IsLocalRequest())
+        {
+            return NotFound();
+        }
+
+        if (!_shutdown.IsLifecycleShutdownAllowed)
+        {
+            return Ok();
+        }
+
+        var delay = TimeSpan.FromSeconds(Math.Max(1, _options.Value.BrowserShutdownDelaySeconds));
+        _shutdown.ScheduleShutdown(delay);
+        return Ok();
+    }
+
+    [HttpPost("cancel-shutdown")]
+    public IActionResult CancelShutdown()
+    {
+        if (!IsShutdownEnabled() || !IsLocalRequest())
+        {
+            return NotFound();
+        }
+
+        _shutdown.CancelScheduledShutdown();
+        return Ok();
+    }
+
+    private bool IsShutdownEnabled() => _options.Value.ExitWhenBrowserCloses;
+
+    private bool IsLocalRequest()
+    {
+        var remote = HttpContext.Connection.RemoteIpAddress;
+        return remote is null || IPAddress.IsLoopback(remote);
+    }
+}

Hosting/DesktopShutdownService.cs

@@ -0,0 +1,117 @@
+using System.Diagnostics;
+
+namespace AVSCartonShipmentVerifier.Hosting;
+
+/// <summary>
+/// Coordinates graceful host shutdown when the desktop browser window or tab is closed.
+/// </summary>
+public sealed class DesktopShutdownService
+{
+    private readonly IHostApplicationLifetime _lifetime;
+    private readonly ILogger<DesktopShutdownService> _logger;
+    private readonly object _gate = new();
+    private CancellationTokenSource? _delayedShutdownCts;
+    private int _shutdownInitiated;
+    private int _dashboardSessionActive;
+
+    public DesktopShutdownService(
+        IHostApplicationLifetime lifetime,
+        ILogger<DesktopShutdownService> logger)
+    {
+        _lifetime = lifetime;
+        _logger = logger;
+    }
+
+    public void MarkDashboardSessionActive()
+    {
+        Interlocked.Exchange(ref _dashboardSessionActive, 1);
+    }
+
+    public bool IsLifecycleShutdownAllowed => Volatile.Read(ref _dashboardSessionActive) == 1;
+
+    public void RequestShutdown(string reason)
+    {
+        if (Interlocked.Exchange(ref _shutdownInitiated, 1) != 0)
+        {
+            return;
+        }
+
+        _logger.LogInformation("Stopping application: {Reason}", reason);
+        _lifetime.StopApplication();
+    }
+
+    public void ScheduleShutdown(TimeSpan delay)
+    {
+        if (!IsLifecycleShutdownAllowed)
+        {
+            _logger.LogDebug("Ignored lifecycle shutdown request before dashboard session was active.");
+            return;
+        }
+
+        lock (_gate)
+        {
+            _delayedShutdownCts?.Cancel();
+            _delayedShutdownCts?.Dispose();
+            _delayedShutdownCts = new CancellationTokenSource();
+            var token = _delayedShutdownCts.Token;
+
+            _ = Task.Run(async () =>
+            {
+                try
+                {
+                    await Task.Delay(delay, token).ConfigureAwait(false);
+                    RequestShutdown("Browser session ended");
+                }
+                catch (OperationCanceledException)
+                {
+                    // Reload or cancel-shutdown superseded this timer.
+                }
+            }, token);
+        }
+    }
+
+    public void CancelScheduledShutdown()
+    {
+        lock (_gate)
+        {
+            if (_delayedShutdownCts is null)
+            {
+                return;
+            }
+
+            _delayedShutdownCts.Cancel();
+            _delayedShutdownCts.Dispose();
+            _delayedShutdownCts = null;
+        }
+    }
+
+    public void WatchBrowserProcess(Process process, TimeSpan minimumLifetime)
+    {
+        var processId = process.Id;
+        var startedUtc = DateTime.UtcNow;
+
+        _ = Task.Run(async () =>
+        {
+            try
+            {
+                await process.WaitForExitAsync().ConfigureAwait(false);
+                var lifetime = DateTime.UtcNow - startedUtc;
+
+                if (lifetime < minimumLifetime)
+                {
+                    _logger.LogInformation(
+                        "Browser launcher process (PID {ProcessId}) exited after {LifetimeSeconds:F1}s; likely handoff to an existing browser. Process tracking disabled; application will keep running.",
+                        processId,
+                        lifetime.TotalSeconds);
+                    return;
+                }
+
+                RequestShutdown("Browser window closed");
+            }
+            catch (Exception ex)
+            {
+                _logger.LogDebug(ex, "Browser process watch ended unexpectedly for PID {ProcessId}.", processId);
+            }
+        });
+    }
+}

Views/Shared/_Layout.cshtml

@@ -1,3 +1,6 @@
+@using AVSCartonShipmentVerifier.Configuration
+@using Microsoft.Extensions.Options
+@inject IOptions<DesktopHostOptions> DesktopHostOptions
 <!DOCTYPE html>
 <html lang="en">
 <head>
@@ -15,6 +18,10 @@
     </div>
 
     <script src="~/lib/bootstrap/dist/js/bootstrap.bundle.min.js"></script>
+    @if (DesktopHostOptions.Value.ExitWhenBrowserCloses)
+    {
+        <script src="~/js/desktop-lifecycle.js" asp-append-version="true"></script>
+    }
     @await RenderSectionAsync("Scripts", required: false)
 </body>
 </html>

wwwroot/js/desktop-lifecycle.js

@@ -0,0 +1,41 @@
+(() => {
+    const scheduleUrl = "/api/desktop/schedule-shutdown";
+    const cancelUrl = "/api/desktop/cancel-shutdown";
+    const registerUrl = "/api/desktop/register-session";
+
+    let sessionRegistered = false;
+
+    const post = (url) => {
+        if (typeof navigator.sendBeacon === "function") {
+            navigator.sendBeacon(url, "");
+            return;
+        }
+
+        fetch(url, { method: "POST", keepalive: true }).catch(() => { });
+    };
+
+    const registerSession = () => {
+        fetch(registerUrl, { method: "POST", keepalive: true })
+            .then((response) => {
+                if (response.ok) {
+                    sessionRegistered = true;
+                    post(cancelUrl);
+                }
+            })
+            .catch(() => { });
+    };
+
+    if (document.readyState === "loading") {
+        document.addEventListener("DOMContentLoaded", registerSession, { once: true });
+    } else {
+        registerSession();
+    }
+
+    window.addEventListener("pagehide", (event) => {
+        if (event.persisted || !sessionRegistered) {
+            return;
+        }
+
+        post(scheduleUrl);
+    });
+})();