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

tests/Paca.Tests/Core/DownloadSelfHealingEngineGateTests.cs

@@ -0,0 +1,57 @@
+using System;
+using Paca.Mobile.Core;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+/// <summary>
+/// Gate 175 ~ 178: 지능형 실패 진단 및 스마트 자가 치유(Self-Healing) 엔진 기계적 검증
+/// </summary>
+public class DownloadSelfHealingEngineGateTests
+{
+    [Fact]
+    public void Gate175_FailureDiagnostics_Classifies_429_RateLimit()
+    {
+        var rawError = "HTTP 429 Too Many Requests: Rate limit exceeded by YouTube server";
+        var diag = DownloadFailureDiagnostics.Analyze(rawError, httpStatusCode: 429);
+
+        Assert.Equal(FailureCategory.RateLimited, diag.Category);
+        Assert.True(diag.CanAutoRetry);
+        Assert.Equal(TimeSpan.FromSeconds(60), diag.SuggestedDelay);
+        Assert.Contains("요청 한도", diag.UserFriendlyMessage);
+    }
+
+    [Fact]
+    public void Gate176_FailureDiagnostics_Classifies_DiskFull()
+    {
+        var rawError = "System.IO.IOException: There is not enough space on the disk";
+        var diag = DownloadFailureDiagnostics.Analyze(rawError);
+
+        Assert.Equal(FailureCategory.DiskFull, diag.Category);
+        Assert.False(diag.CanAutoRetry); // 디스크 공간 부족은 자동 재시도 불가(수동 정리 필요)
+        Assert.Contains("저장 공간", diag.UserFriendlyMessage);
+    }
+
+    [Fact]
+    public void Gate177_FailureDiagnostics_Classifies_NetworkLoss_And_Enables_AutoResume()
+    {
+        var rawError = "System.Net.Sockets.SocketException: The network connection was lost";
+        var diag = DownloadFailureDiagnostics.Analyze(rawError);
+
+        Assert.Equal(FailureCategory.NetworkLoss, diag.Category);
+        Assert.True(diag.CanAutoRetry);
+        Assert.True(diag.CanAutoResume); // 이어받기 가능
+        Assert.Contains("인터넷 연결", diag.UserFriendlyMessage);
+    }
+
+    [Theory]
+    [InlineData(1, 5)]   // 1회차: 5초
+    [InlineData(2, 10)]  // 2회차: 10초
+    [InlineData(3, 20)]  // 3회차: 20초
+    [InlineData(4, 40)]  // 4회차: 40초
+    public void Gate178_SelfHealingStrategy_ExponentialBackoff(int attempt, int expectedSeconds)
+    {
+        var delay = SelfHealingActionStrategy.CalculateExponentialBackoff(attempt, baseDelaySec: 5, maxDelaySec: 60);
+        Assert.Equal(TimeSpan.FromSeconds(expectedSeconds), delay);
+    }
+}