releases/tests/Paca.Tests/Mobile/MobileResponsivenessAndAnrPreventionGateTests.cs

using System;
using System.IO;
using System.Threading;
using System.Threading.Tasks;
using Paca.Mobile;
using Paca.Mobile.Core;
using Xunit;

namespace Paca.Tests.Mobile;

public class MobileResponsivenessAndAnrPreventionGateTests
{
    private static readonly string RepoRoot = FindRepoRoot();
    private static readonly string MobileCoreDir = Path.Combine(RepoRoot, "src", "Paca.Mobile.Core");
    private static readonly string MobileDir = Path.Combine(RepoRoot, "src", "Paca.Mobile");

    private static string FindRepoRoot()
    {
        var dir = AppContext.BaseDirectory;
        while (!string.IsNullOrEmpty(dir))
        {
            if (File.Exists(Path.Combine(dir, "Paca.slnx")) || Directory.Exists(Path.Combine(dir, "src", "Paca.Mobile.Core")))
                return dir;
            var parent = Directory.GetParent(dir);
            if (parent == null) break;
            dir = parent.FullName;
        }
        return Path.GetFullPath(Path.Combine(AppContext.BaseDirectory, "..", "..", "..", "..", ".."));
    }

    [Fact]
    public void Gate190_InteractionDebouncer_PreventsRapidDoubleTap_AndAllowsAfterCooldown()
    {
        MobileInteractionDebouncer.Reset();

        // First tap succeeds
        Assert.True(MobileInteractionDebouncer.TryBeginInteraction(cooldownMs: 350));

        // Immediate subsequent tap (within 350ms) is blocked to prevent concurrent modal pushes / ANR
        Assert.False(MobileInteractionDebouncer.TryBeginInteraction(cooldownMs: 350));

        // After cooldown, interaction is allowed again
        Thread.Sleep(360);
        Assert.True(MobileInteractionDebouncer.TryBeginInteraction(cooldownMs: 350));
    }

    [Fact]
    public void Gate191_ScrollThrottler_EnforcesRateLimit_AndFiltersHighFrequencyNoise()
    {
        var throttler = new MobileScrollThrottler(minIntervalMs: 16, minDeltaThreshold: 10);

        // 1. Initial scroll event passes
        Assert.True(throttler.ShouldProcess(scrollY: 50, deltaY: 20));

        // 2. High-frequency tick within 16ms window is throttled
        Assert.False(throttler.ShouldProcess(scrollY: 52, deltaY: 2));

        // 3. Tick with negligible delta (< minDeltaThreshold) is ignored
        Thread.Sleep(20);
        Assert.False(throttler.ShouldProcess(scrollY: 53, deltaY: 1));

        // 4. Meaningful scroll after frame window passes
        Thread.Sleep(20);
        Assert.True(throttler.ShouldProcess(scrollY: 85, deltaY: 32));

        // 5. Scroll to top (scrollY <= 20) always forces pass regardless of delta
        Assert.True(throttler.ShouldProcess(scrollY: 5, deltaY: -5));
    }

    [Fact]
    public void Gate192_SafeAreaCoordinator_DeadbandHysteresis_RejectsSubpixelJitter()
    {
        var coordinator = new MobileSafeAreaCoordinator();
        int eventCount = 0;
        coordinator.InsetsChanged += () => eventCount++;

        // 1. Initial non-zero update fires event
        coordinator.UpdateInsets(bottomDp: 48.0, topDp: 42.0, keyboardDp: 0.0);
        Assert.Equal(1, eventCount);
        Assert.Equal(48.0, coordinator.BottomInsetDp);
        Assert.Equal(42.0, coordinator.TopInsetDp);

        // 2. Subpixel jitter (< 1.0dp difference) must NOT fire event (prevents infinite layout loops)
        coordinator.UpdateInsets(bottomDp: 48.3, topDp: 42.2, keyboardDp: 0.0);
        Assert.Equal(1, eventCount); // Still 1! No new event fired

        // 3. Significant inset change (>= 1.0dp) must fire event
        coordinator.UpdateInsets(bottomDp: 0.0, topDp: 42.0, keyboardDp: 0.0);
        Assert.Equal(2, eventCount);
        Assert.Equal(0.0, coordinator.BottomInsetDp);

        // 4. Keyboard open (IME insets) fires event
        coordinator.UpdateInsets(bottomDp: 0.0, topDp: 42.0, keyboardDp: 280.0);
        Assert.Equal(3, eventCount);
        Assert.Equal(280.0, coordinator.KeyboardInsetDp);
    }

    [Fact]
    public void Gate193_PlatformSourceAudit_ProhibitsHighFrequencyLoggingInScrollAndLayout()
    {
        var customizerCs = File.ReadAllText(Path.Combine(MobileDir, "Platforms", "Android", "PacaAndroidWebViewCustomizer.cs"));
        var browserCs = File.ReadAllText(Path.Combine(MobileDir, "BrowserPage.cs"));

        // Native scroll listener must NOT log verbose lines on every 120Hz tick
        Assert.DoesNotContain("Log.Info(\"PacaTrace\", $\">>> NativeScroll", customizerCs);

        // BrowserPage AnimateTopBar must protect against re-entrancy and layout oscillation
        Assert.Contains("show == !_isTopBarHidden || _isTopBarAnimating", browserCs);

        // Menu button and quick actions must employ interaction debouncing
        Assert.Contains("MobileInteractionDebouncer.TryBeginInteraction", browserCs);
    }

    [Fact]
    public async Task Gate194_StoreSaveConcurrency_SemaphoreSlimProtection_PreventsIoCollision()
    {
        var tempFile = Path.Combine(Path.GetTempPath(), $"paca_history_test_{Guid.NewGuid():N}.json");
        try
        {
            var store = new MobileHistoryStore(tempFile);

            // 30 concurrent rapid visit writes
            var tasks = new Task[30];
            for (int i = 0; i < 30; i++)
            {
                int index = i;
                tasks[i] = Task.Run(async () =>
                {
                    await store.AddVisitAsync($"https://example.com/item/{index}", $"Item {index}");
                });
            }

            await Task.WhenAll(tasks);

            var items = store.GetRecent(50);
            Assert.Equal(30, items.Count);
        }
        finally
        {
            try { if (File.Exists(tempFile)) File.Delete(tempFile); } catch { }
            try { if (File.Exists(tempFile + ".tmp")) File.Delete(tempFile + ".tmp"); } catch { }
        }
    }

    [Fact]
    public async Task Gate195_BookmarkStore_SaveConcurrency_SemaphoreSlimProtection()
    {
        var tempFile = Path.Combine(Path.GetTempPath(), $"paca_bookmark_test_{Guid.NewGuid():N}.json");
        try
        {
            var store = new MobileBookmarkStore(tempFile);

            // 30 concurrent bookmark additions
            var tasks = new Task[30];
            for (int i = 0; i < 30; i++)
            {
                int index = i;
                tasks[i] = Task.Run(async () =>
                {
                    await store.AddOrUpdateBookmarkAsync($"https://example.com/b/{index}", $"Bookmark {index}");
                });
            }

            await Task.WhenAll(tasks);

            var all = store.GetAll();
            Assert.Equal(30, all.Count);
        }
        finally
        {
            try { if (File.Exists(tempFile)) File.Delete(tempFile); } catch { }
            try { if (File.Exists(tempFile + ".tmp")) File.Delete(tempFile + ".tmp"); } catch { }
        }
    }

    [Fact]
    public void Gate196_AllToolbarButtons_AndActions_CoveredByDebouncer()
    {
        var browserCs = File.ReadAllText(Path.Combine(MobileDir, "BrowserPage.cs"));
        var menuCs = File.ReadAllText(Path.Combine(MobileDir, "MobileMenuModal.cs"));

        // Toolbar buttons must check debouncer
        Assert.Contains("ToolbarTabsBtn", browserCs);
        Assert.Contains("MobileInteractionDebouncer.TryBeginInteraction()", browserCs);

        // Menu tiles and rows must check debouncer
        Assert.Contains("MobileInteractionDebouncer.TryBeginInteraction()", menuCs);
    }

    [Fact]
    public void Gate197_NoDoubleDebouncing_BetweenToolbarButtonAndMenuOpen()
    {
        var browserCs = File.ReadAllText(Path.Combine(MobileDir, "BrowserPage.cs"));

        // OpenMoreMenuAsync must NOT call TryBeginInteraction because CreateToolbarButton already performs it!
        // (Calling it twice in the same call stack causes immediate self-blocking within 0ms)
        var methodIdx = browserCs.IndexOf("private async Task OpenMoreMenuAsync()");
        Assert.True(methodIdx > 0);
        var methodBody = browserCs.Substring(methodIdx, 300);
        Assert.DoesNotContain("MobileInteractionDebouncer.TryBeginInteraction", methodBody);
    }

    [Fact]
    public void Gate198_NavigationGuard_EnforcesSingleFlight_AndAutoRecoversOnTimeout()
    {
        MobileNavigationGuard.Reset();

        // 1. Initial navigation begins successfully
        Assert.True(MobileNavigationGuard.TryBeginNavigation(timeoutMs: 200));

        // 2. Concurrent second navigation is rejected (prevents FragmentManager collision / ANR)
        Assert.False(MobileNavigationGuard.TryBeginNavigation(timeoutMs: 200));

        // 3. Normal completion frees lock immediately
        MobileNavigationGuard.EndNavigation();
        Assert.True(MobileNavigationGuard.TryBeginNavigation(timeoutMs: 200));

        // 4. If navigation hangs or crashes without EndNavigation, auto-recovery frees lock after timeout
        Thread.Sleep(250);
        Assert.True(MobileNavigationGuard.TryBeginNavigation(timeoutMs: 200));
        MobileNavigationGuard.EndNavigation();
    }

    [Fact]
    public async Task Gate199_NavigationGuard_SafeModalToPageSequencing_CoordinatesTransitions()
    {
        int sequence = 0;
        int dismissStep = 0;
        int pushStep = 0;

        await MobileNavigationGuard.CoordinateModalToPageTransitionAsync(
            dismissModalAsync: async () =>
            {
                await Task.Delay(20);
                dismissStep = ++sequence;
            },
            pushPageAsync: async () =>
            {
                await Task.Delay(10);
                pushStep = ++sequence;
            },
            interTransitionDelayMs: 30
        );

        Assert.Equal(1, dismissStep);
        Assert.Equal(2, pushStep);
        Assert.True(pushStep > dismissStep);
    }

    [Fact]
    public void Gate200_DownloadProgressThrottler_FiltersRapidFlooding_AndGuaranteesTerminalTransitions()
    {
        var throttler = new MobileDownloadProgressThrottler(minIntervalMs: 100, minDeltaPercent: 1.0);
        const string taskId = "task-101";

        // 1. Initial active download tick passes
        Assert.True(throttler.ShouldDispatchProgress(taskId, 5.0, MobileDownloadStatus.Downloading));

        // 2. Rapid ticks (within 100ms and < 1% delta) are throttled out
        Assert.False(throttler.ShouldDispatchProgress(taskId, 5.2, MobileDownloadStatus.Downloading));
        Assert.False(throttler.ShouldDispatchProgress(taskId, 5.5, MobileDownloadStatus.Downloading));

        // 3. Significant delta (>= 1.0%) passes immediately even within interval
        Assert.True(throttler.ShouldDispatchProgress(taskId, 6.6, MobileDownloadStatus.Downloading));

        // 4. After interval passes, even minor delta passes
        Thread.Sleep(120);
        Assert.True(throttler.ShouldDispatchProgress(taskId, 6.8, MobileDownloadStatus.Downloading));

        // 5. Terminal status (Completed/Failed/Cancelled) ALWAYS passes immediately
        Assert.True(throttler.ShouldDispatchProgress(taskId, 100.0, MobileDownloadStatus.Completed));
    }

    [Fact]
    public async Task Gate201_WebViewScriptGuard_TimesOutHungScript_AndReturnsFallbackWithoutCrash()
    {
        // 1. Fast script succeeds
        var fastResult = await MobileWebViewScriptGuard.ExecuteWithTimeoutAsync(
            async ct =>
            {
                await Task.Delay(10, ct);
                return "{\"ready\":true}";
            },
            timeoutMs: 200,
            fallback: "fallback"
        );
        Assert.Equal("{\"ready\":true}", fastResult);

        // 2. Hung script (e.g. alert dialog or infinite loop in JS) times out and returns fallback safely
        var hungResult = await MobileWebViewScriptGuard.ExecuteWithTimeoutAsync(
            async ct =>
            {
                await Task.Delay(500, ct);
                return "never";
            },
            timeoutMs: 100,
            fallback: "fallback_timeout"
        );
        Assert.Equal("fallback_timeout", hungResult);
    }

    [Fact]
    public async Task Gate202_AsyncShield_CatchesAndLogsExceptions_WithoutCrashingProcessOrFreezing()
    {
        Exception? caught = null;

        await MobileAsyncShield.ExecuteSafeAsync(
            async () =>
            {
                await Task.Yield();
                throw new InvalidOperationException("Simulated navigation collision");
            },
            onError: ex => caught = ex,
            tag: "TestGate202"
        );

        Assert.NotNull(caught);
        Assert.IsType<InvalidOperationException>(caught);
        Assert.Equal("Simulated navigation collision", caught.Message);
    }

    [Fact]
    public void Gate203_CodebaseAudit_ToolbarAndNavigation_GuardedAgainstReentrancy()
    {
        var browserCs = File.ReadAllText(Path.Combine(MobileDir, "BrowserPage.cs"));
        var menuCs = File.ReadAllText(Path.Combine(MobileDir, "MobileMenuModal.cs"));

        // BrowserPage must reference MobileNavigationGuard
        Assert.Contains("MobileNavigationGuard", browserCs);

        // MobileMenuModal must reference MobileNavigationGuard
        Assert.Contains("MobileNavigationGuard", menuCs);
    }

    [Fact]
    public void Gate204_CodebaseAudit_DownloadsPage_UsesProgressThrottling()
    {
        var downloadsCs = File.ReadAllText(Path.Combine(MobileDir, "DownloadsPage.cs"));

        // DownloadsPage must not blindly re-render on every raw progress tick without throttler
        Assert.Contains("MobileDownloadProgressThrottler", downloadsCs);
    }

    [Fact]
    public void Gate205_CodebaseAudit_AllToolbarActions_ProtectedByAsyncShield()
    {
        var browserCs = File.ReadAllText(Path.Combine(MobileDir, "BrowserPage.cs"));

        // CreateToolbarButton must use MobileAsyncShield to prevent unobserved task crash
        Assert.Contains("MobileAsyncShield.ExecuteSafeAsync", browserCs);
    }

    [Fact]
    public void Gate206_ApiClient_Architecture_PureConstructor_And_LazyInitialization()
    {
        var sw = System.Diagnostics.Stopwatch.StartNew();
        var storage = new InMemoryKeyValueStorage();
        var client = new ApiClient(storage: storage);
        sw.Stop();

        // Constructor must be O(1) pure, under 5ms, zero I/O
        Assert.True(sw.ElapsedMilliseconds < 5, $"ApiClient constructor took too long: {sw.ElapsedMilliseconds}ms");
        Assert.False(client.IsConfigured);

        // Configure persists to storage
        bool configured = client.Configure("http://192.168.1.100:52100/#t=test_token_123&cc=7777");
        Assert.True(configured);
        Assert.True(client.IsConfigured);
        Assert.Equal("http://192.168.1.100:52100", client.BaseUrl);
        Assert.Equal("test_token_123", client.Token);
        Assert.Equal("7777", client.ConnectCode);
        Assert.Equal("http://192.168.1.100:52100", storage.Get("vd_base", ""));

        // New client restoring from storage
        var restoredClient = new ApiClient(storage: storage);
        Assert.False(restoredClient.IsConfigured); // Not configured until restored
        restoredClient.Restore();
        Assert.True(restoredClient.IsConfigured);
        Assert.Equal("http://192.168.1.100:52100", restoredClient.BaseUrl);
    }

    [Fact]
    public async Task Gate207_ApiClient_HighConcurrency_NoDeadlock_UnderMultiThreadAccess()
    {
        var storage = new InMemoryKeyValueStorage();
        storage.Set("vd_base", "http://10.0.0.1:52100");
        storage.Set("vd_token", "concurrent_token");
        var client = new ApiClient(storage: storage);
        client.Restore();

        var cts = new CancellationTokenSource(TimeSpan.FromSeconds(2));
        var tasks = new Task[50];

        for (int i = 0; i < tasks.Length; i++)
        {
            tasks[i] = Task.Run(() =>
            {
                for (int j = 0; j < 1000; j++)
                {
                    cts.Token.ThrowIfCancellationRequested();
                    var isConf = client.IsConfigured;
                    if (j % 100 == 0)
                    {
                        var url = client.BaseUrl;
                    }
                }
            }, cts.Token);
        }

        // All 50 threads must finish 50,000 accesses within 2 seconds with zero deadlock
        await Task.WhenAll(tasks);
        Assert.True(client.IsConfigured);
    }

    [Fact]
    public async Task Gate208_ApiClient_NetworkResilience_TimeoutAndFailureHandling()
    {
        var client = new ApiClient(); // Unconfigured client
        Assert.False(client.IsConfigured);

        var queue = await client.GetQueueAsync();
        Assert.Empty(queue);

        var addResult = await client.AddAsync("https://example.com/video.mp4");
        Assert.False(addResult);

        var lib = await client.GetLibraryAsync();
        Assert.Empty(lib);
    }

    [Fact]
    public void Gate209_CodebaseAudit_ZeroSynchronousTaskBlockingOnMainThread()
    {
        // Forbid .Result, .Wait(), and .GetAwaiter().GetResult() across Mobile codebase to prevent ANR
        var csFiles = Directory.GetFiles(MobileDir, "*.cs", SearchOption.AllDirectories);
        var forbiddenPatterns = new[] { ".GetAwaiter().GetResult()", ".Wait()", ".Result" };

        foreach (var file in csFiles)
        {
            var fileName = Path.GetFileName(file);
            // Skip designer/generated/interop files if any
            if (fileName.EndsWith(".g.cs") || fileName.Contains("Resource")) continue;

            var content = File.ReadAllText(file);
            foreach (var pattern in forbiddenPatterns)
            {
                // Ensure no synchronous task blocking in mobile UI code
                if (content.Contains(pattern))
                {
                    // Allow legitimate pattern matches if guarded or in comments
                    var lines = content.Split('\n');
                    for (int i = 0; i < lines.Length; i++)
                    {
                        var line = lines[i].Trim();
                        if (line.StartsWith("//") || line.StartsWith("/*")) continue;
                        if (line.Contains(pattern))
                        {
                            // If it's a Property named Result (like DialogResult, HttpResult), ignore
                            if (pattern == ".Result" && (line.Contains("DialogResult") || line.Contains("r.Result") == false && line.Contains("Task") == false && line.Contains("task.") == false))
                                continue;
                            Assert.Fail($"Forbidden synchronous blocking call '{pattern}' found in {fileName}:{i + 1} -> '{line}'. This causes Android ANR!");
                        }
                    }
                }
            }
        }
    }

    [Fact]
    public void Gate210_MobileMenuContext_SnapshotGeneration_NonBlockingAndInstant()
    {
        // Warm-up to avoid cold JIT measurement artifact
        _ = new MobileMenuContext("https://warmup", "Title", false, MobileThemeMode.Dark, false, 0, false);

        var sw = System.Diagnostics.Stopwatch.StartNew();
        var context = new MobileMenuContext(
            CurrentUrl: "https://youtube.com/watch?v=123",
            CurrentTitle: "Awesome Video",
            IsDesktopMode: false,
            ThemeMode: MobileThemeMode.Dark,
            IsBookmarked: true,
            SniffedVideoCount: 3,
            IsP2pConnected: false
        );
        sw.Stop();

        Assert.True(sw.ElapsedMilliseconds < 10, "Menu context creation must be instant (< 10ms)");
        Assert.True(context.IsBookmarked);
        Assert.Equal(3, context.SniffedVideoCount);
        Assert.False(context.IsP2pConnected);
    }

    [Fact]
    public void Gate211_CodebaseAudit_ApiClient_PureConstructor_NoDirectPreferencesInConstructor()
    {
        var coreApiClient = Path.Combine(MobileCoreDir, "ApiClient.cs");
        var mobileApiClient = Path.Combine(MobileDir, "ApiClient.cs");
        var targetPath = File.Exists(coreApiClient) ? coreApiClient : mobileApiClient;

        var content = File.ReadAllText(targetPath);

        // Constructor must NOT contain Preferences.Get or direct I/O
        var ctorIndex = content.IndexOf("public ApiClient(");
        if (ctorIndex == -1) ctorIndex = content.IndexOf("ApiClient(");
        Assert.True(ctorIndex >= 0, "ApiClient must declare a constructor");

        // The constructor block must not call Preferences.Get or Restore()
        var ctorBlock = content.Substring(ctorIndex, Math.Min(300, content.Length - ctorIndex));
        Assert.DoesNotContain("Preferences.Get", ctorBlock);
        Assert.DoesNotContain("Restore();", ctorBlock);
    }

    [Fact]
    public void Gate212_CodebaseAudit_MobilePages_EventUnsubscriptionLifecycle()
    {
        var downloadsCs = File.ReadAllText(Path.Combine(MobileDir, "DownloadsPage.cs"));

        // DownloadsPage must override OnDisappearing and unsubscribe from singleton events to prevent memory leaks and ghost refreshes
        Assert.Contains("protected override void OnDisappearing()", downloadsCs);
        Assert.Contains("TasksChanged -=", downloadsCs);
        Assert.Contains("TaskProgressUpdated -=", downloadsCs);
        Assert.Contains("InsetsChanged -=", downloadsCs);
    }

    [Fact]
    public void Gate213_CodebaseAudit_AllBackButtons_And_Pops_GuardedAgainstReentrancy()
    {
        var pagesToCheck = new[] { "DownloadsPage.cs", "HistoryBookmarksPage.cs", "SyncSettingsPage.cs", "TabManagerPage.cs" };

        foreach (var pageFile in pagesToCheck)
        {
            var content = File.ReadAllText(Path.Combine(MobileDir, pageFile));

            // Must reference MobileNavigationGuard.SafePopAsync to prevent concurrent FragmentManager pops / ANR
            Assert.Contains("MobileNavigationGuard.SafePopAsync", content);
        }
    }

    [Fact]
    public void Gate214_CodebaseAudit_DownloadsPage_SeparateTabRendering_ActiveDoesNotTouchOffline()
    {
        var downloadsCs = File.ReadAllText(Path.Combine(MobileDir, "DownloadsPage.cs"));

        // Must have separate RenderActiveTasks and RenderOfflineLibrary methods to avoid scanning disk during active download progress
        Assert.Contains("RenderActiveTasks()", downloadsCs);
        Assert.Contains("RenderOfflineLibrary()", downloadsCs);

        // TaskProgressUpdated must only re-render active tasks if active segment is selected
        Assert.Contains("RenderActiveTasks", downloadsCs);
    }

    [Fact]
    public async Task Gate215_OfflineStore_HighConcurrency_ThreadSafe_NoDeadlock()
    {
        var tempDir = Path.Combine(Path.GetTempPath(), $"paca_offline_store_{Guid.NewGuid():N}");
        Directory.CreateDirectory(tempDir);
        try
        {
            var store = new OfflineStore(tempDir);
            Directory.CreateDirectory(store.Directory);

            // 50 concurrent tasks performing Record, List, and Delete
            var tasks = new Task[50];
            for (int i = 0; i < 50; i++)
            {
                int index = i;
                tasks[i] = Task.Run(() =>
                {
                    var id = $"item_{index}";
                    var dummyFile = store.PathFor(id);
                    File.WriteAllText(dummyFile, "dummy data payload");

                    store.Record(id, $"video_{index}.mp4");
                    Assert.True(store.Exists(id));

                    var list = store.List();
                    Assert.NotEmpty(list);

                    if (index % 2 == 0)
                    {
                        store.Delete(id);
                    }
                });
            }

            // Must finish within 3 seconds with zero deadlock or file access collision
            var completed = await Task.WhenAny(Task.WhenAll(tasks), Task.Delay(3000));
            Assert.NotEqual(completed, Task.Delay(3000)); // Did not timeout
            await Task.WhenAll(tasks);
        }
        finally
        {
            try { Directory.Delete(tempDir, recursive: true); } catch { }
        }
    }

    [Fact]
    public async Task Gate216_MobileNavigationGuard_SafePopAsync_PreventsConcurrentPops()
    {
        MobileNavigationGuard.Reset();

        int popCount = 0;
        var tcs = new TaskCompletionSource<bool>();

        // 1. Launch first pop that is suspended on tcs
        var firstPopTask = MobileNavigationGuard.SafePopAsync(async () =>
        {
            popCount++;
            await tcs.Task;
        });

        // 2. Second concurrent pop must be rejected immediately by guard
        bool secondPopExecuted = false;
        await MobileNavigationGuard.SafePopAsync(async () =>
        {
            secondPopExecuted = true;
            await Task.Yield();
        });

        Assert.False(secondPopExecuted, "Concurrent pop must be safely rejected to protect FragmentManager");
        Assert.Equal(1, popCount);

        // 3. Complete first pop
        tcs.SetResult(true);
        await firstPopTask;

        // 4. Subsequent pop after first completes is accepted
        bool thirdPopExecuted = false;
        await MobileNavigationGuard.SafePopAsync(async () =>
        {
            thirdPopExecuted = true;
            await Task.Yield();
        });

        Assert.True(thirdPopExecuted);
    }

    [Fact]
    public void Gate217_LanDiscoveryProber_TimeoutAndSafeCancellation()
    {
        using var prober = new LanDiscoveryProber();

        // Feed sample payloads
        prober.HandleReceivedPayload("PACA_DISCOVERY|PONG|Desktop-1|192.168.1.50:52100|1|fp123", "192.168.1.50");
        prober.HandleReceivedPayload("PACA_DISCOVERY|PONG|Desktop-2|:52100|0|fp456", "192.168.1.60"); // Missing IP auto-corrected

        var devices = prober.GetActiveDevices(TimeSpan.FromSeconds(5));
        Assert.Equal(2, devices.Count);
        Assert.Equal("http://192.168.1.50:52100", devices[0].HttpBaseUrl);
        Assert.Equal("192.168.1.60:52100", devices[1].Endpoint);

        // Safe stop without exceptions
        prober.Stop();
    }

    [Fact]
    public void Gate218_CodebaseAudit_NoRawFileIoInsideUiProgressLoops()
    {
        var downloadsCs = File.ReadAllText(Path.Combine(MobileDir, "DownloadsPage.cs"));

        // Inside TaskProgressUpdated handler, there must not be any direct calls to AppOfflineStore.Default.List() or FileInfo
        var progressHandlerIdx = downloadsCs.IndexOf("TaskProgressUpdated +=");
        Assert.True(progressHandlerIdx > 0);

        var progressHandlerBlock = downloadsCs.Substring(progressHandlerIdx, Math.Min(300, downloadsCs.Length - progressHandlerIdx));
        Assert.DoesNotContain("AppOfflineStore.Default.List()", progressHandlerBlock);
        Assert.DoesNotContain("FileInfo", progressHandlerBlock);
    }
}