feat(ads/seo/release): v1.2.0 with live Google Ads, isolated ad profile, ads.txt, and SEO/AEO/GEO optimization

tests/Paca.Tests/Platform/CrossPlatformParityHardeningPhase5Tests.cs

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+using System;
+using System.IO;
+using System.Linq;
+using Paca.Avalonia;
+using Paca.Mobile.Core;
+using Xunit;
+
+namespace Paca.Tests.Platform;
+
+/// <summary>
+/// Phase 5: 크로스플랫폼 패리티 및 모바일/데스크톱 견고성 헌법 게이트 (Gate 501 ~ 503).
+/// - Gate 501: Paca.Avalonia MainViewModel 일시정지/재개(Pause/Resume) 및 IDisposable 생명주기
+/// - Gate 502: Paca.Mobile.Core LanDiscoveryProber 널 안전성, IPv6 및 P2P QR TTL 만료 검증
+/// - Gate 503: Paca.Mobile.Core SmartCollectionEngine 널 타이틀 방어 및 M3U8 개행문자 살균
+/// </summary>
+public class CrossPlatformParityHardeningPhase5Tests
+{
+    [Fact]
+    public void Gate501_Avalonia_MainViewModel_Pause_Resume_And_Disposable_Lifecycle_Audit()
+    {
+        using var vm = new MainViewModel();
+
+        // 1. IDisposable 구현 검증
+        Assert.IsAssignableFrom<IDisposable>(vm);
+
+        // 2. PauseCommand & ResumeCommand 배선 확인
+        Assert.NotNull(vm.PauseCommand);
+        Assert.NotNull(vm.ResumeCommand);
+        Assert.NotNull(vm.DownloadCommand);
+        Assert.NotNull(vm.CancelCommand);
+
+        // 3. 초기 상태: IsBusy=false, IsPaused=false, CanExecute 검증
+        Assert.False(vm.IsBusy);
+        Assert.False(vm.IsPaused);
+        Assert.False(vm.PauseCommand.CanExecute(null));
+        Assert.False(vm.ResumeCommand.CanExecute(null));
+
+        // 4. IsBusy 상태 시뮬레이션
+        vm.IsBusy = true;
+        Assert.True(vm.PauseCommand.CanExecute(null));
+        Assert.False(vm.ResumeCommand.CanExecute(null));
+
+        // 5. 일시정지(Pause) 실행
+        vm.Pause();
+        Assert.True(vm.IsPaused);
+        Assert.Equal("일시정지됨", vm.Status);
+        Assert.False(vm.PauseCommand.CanExecute(null));
+        Assert.True(vm.ResumeCommand.CanExecute(null));
+
+        // 6. 재개(Resume) 실행
+        vm.Resume();
+        Assert.False(vm.IsPaused);
+        Assert.Equal("다운로드 재개 중...", vm.Status);
+        Assert.True(vm.PauseCommand.CanExecute(null));
+        Assert.False(vm.ResumeCommand.CanExecute(null));
+
+        // 7. 다운로드 완료(IsBusy=false) 시 IsPaused 자동 초기화
+        vm.Pause();
+        Assert.True(vm.IsPaused);
+        vm.IsBusy = false;
+        Assert.False(vm.IsPaused);
+        Assert.False(vm.PauseCommand.CanExecute(null));
+        Assert.False(vm.ResumeCommand.CanExecute(null));
+    }
+
+    [Fact]
+    public void Gate502_LanDiscoveryProber_Robust_Address_And_NullSafe_Packet_Handling_Audit()
+    {
+        var prober = new LanDiscoveryProber();
+
+        // 1. Null/Whitespace 페이로드 안전성 (예외 미발생)
+        prober.HandleReceivedPayload(null!, null!);
+        prober.HandleReceivedPayload("", "192.168.1.50");
+        prober.HandleReceivedPayload("   ", "");
+
+        // 2. RemoteIp가 null/빈값인 경우 127.0.0.1 기본 폴백
+        var pong = LanDiscoveryMessage.CreatePong("PC-NullIp", ":5000", true, "FP-001");
+        prober.HandleReceivedPayload(pong.ToPayload(), null!);
+        var devices = prober.GetActiveDevices();
+        var devNullIp = devices.FirstOrDefault(d => d.DeviceName == "PC-NullIp");
+        Assert.NotNull(devNullIp);
+        Assert.Equal("127.0.0.1:5000", devNullIp.Endpoint);
+
+        // 3. IPv6 remoteIp의 브래킷([]) 포맷팅 검증
+        var pongIpv6 = LanDiscoveryMessage.CreatePong("PC-IPv6", ":52100", true, "FP-IPV6");
+        prober.HandleReceivedPayload(pongIpv6.ToPayload(), "fe80::1");
+        devices = prober.GetActiveDevices();
+        var devIpv6 = devices.FirstOrDefault(d => d.DeviceName == "PC-IPv6");
+        Assert.NotNull(devIpv6);
+        Assert.Equal("[fe80::1]:52100", devIpv6.Endpoint);
+        Assert.Equal("http://[fe80::1]:52100", devIpv6.HttpBaseUrl);
+
+        // 4. P2pQrPayloadCodec TTL 만료 검증
+        var now = DateTimeOffset.UtcNow;
+        var freshPayload = new P2pQrPayload
+        {
+            Host = "192.168.1.10",
+            Port = 5000,
+            Token = "token-fresh",
+            CreatedAtUnix = now.ToUnixTimeSeconds()
+        };
+        var encodedFresh = P2pQrPayloadCodec.Encode(freshPayload);
+        Assert.Contains("&ts=", encodedFresh);
+        var decodedFresh = P2pQrPayloadCodec.Decode(encodedFresh);
+        Assert.Equal(freshPayload.CreatedAtUnix, decodedFresh.CreatedAtUnix);
+        Assert.False(P2pQrPayloadCodec.IsExpired(decodedFresh, TimeSpan.FromMinutes(5), now));
+
+        var expiredPayload = new P2pQrPayload
+        {
+            Host = "192.168.1.10",
+            Port = 5000,
+            Token = "token-expired",
+            CreatedAtUnix = now.AddMinutes(-10).ToUnixTimeSeconds()
+        };
+        var encodedExpired = P2pQrPayloadCodec.Encode(expiredPayload);
+        var decodedExpired = P2pQrPayloadCodec.Decode(encodedExpired);
+        Assert.True(P2pQrPayloadCodec.IsExpired(decodedExpired, TimeSpan.FromMinutes(5), now));
+    }
+
+    [Fact]
+    public void Gate503_SmartCollectionEngine_NullSafe_Title_And_M3u8_Sanitization_Audit()
+    {
+        // 1. Title이 null이거나 빈 문자열인 경우 NRE 없이 정상 분류
+        var itemNullTitle = new MediaItemMetadata(
+            Id: "item-1",
+            Title: null!,
+            Url: "https://youtube.com/shorts/test1234",
+            DurationSeconds: 45,
+            SizeBytes: 1024 * 1024,
+            Format: "mp4"
+        );
+
+        var itemAudio = new MediaItemMetadata(
+            Id: "item-2",
+            Title: "Podcast Episode 1",
+            Url: "https://example.com/audio.mp3",
+            DurationSeconds: 1200,
+            SizeBytes: 20 * 1024 * 1024,
+            Format: "mp3"
+        );
+
+        var itemWithNewlines = new MediaItemMetadata(
+            Id: "item-3",
+            Title: "Title With\r\nDangerous\nNewlines",
+            Url: "https://example.com/video.mp4",
+            DurationSeconds: 300,
+            SizeBytes: 50 * 1024 * 1024,
+            Format: "mp4"
+        );
+
+        var collections = SmartCollectionEngine.GroupIntoCollections(new[] { itemNullTitle, itemAudio, itemWithNewlines });
+        Assert.Contains(itemNullTitle, collections[SmartCollectionEngine.CollectionShorts]);
+        Assert.Contains(itemAudio, collections[SmartCollectionEngine.CollectionMusic]);
+        Assert.Contains(itemWithNewlines, collections[SmartCollectionEngine.CollectionGeneral]);
+
+        // 2. M3U8 플레이리스트 생성 시 개행 문자 살균 검증
+        var m3u8 = SmartCollectionEngine.GenerateM3u8Playlist("Playlist\r\nName", new[] { itemWithNewlines });
+        Assert.DoesNotContain("\r\nDangerous", m3u8);
+        Assert.Contains("#PLAYLIST:Playlist Name", m3u8);
+        Assert.Contains("#EXTINF:300,Title With Dangerous Newlines", m3u8);
+    }
+}