test(core/browser/platform): 26 extreme RED/GREEN TDD cycles and full regression hardening (3,235 PASS)

tests/Paca.Tests/Core/ConcurrencyAndCacheIntegrityExtremeRedTests.cs

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+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Threading.Tasks;
+using Paca.Core.Hls;
+using Paca.Core.Platform;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+/// <summary>
+/// Cycle 4: 극한 RED 시나리오 - 카오스 멀티스레딩 동시성 무결성 및 경로 순회(Path Traversal) / 파일 락 방어선 검증
+/// </summary>
+public class ConcurrencyAndCacheIntegrityExtremeRedTests
+{
+    [Fact]
+    public void Cycle4_Gate1_VideoDeduplicator_ConcurrentStress_MustNotThrowOrCorrupt()
+    {
+        var deduplicator = new VideoDeduplicator(maxHammingThreshold: 5);
+        const int TaskCount = 32;
+        const int IterationsPerTask = 200;
+
+        Parallel.For(0, TaskCount, taskId =>
+        {
+            for (int i = 0; i < IterationsPerTask; i++)
+            {
+                var filePath = $"C:/media/video_{taskId}_{i}.mp4";
+                ulong hash = (ulong)(taskId * 10000 + i);
+
+                // 동시 등록
+                deduplicator.RegisterVideo(filePath, hash);
+
+                // 동시 검색
+                var match = deduplicator.FindDuplicate(hash);
+                Assert.NotNull(match);
+                Assert.Equal(0, match.HammingDistance);
+            }
+        });
+
+        Assert.Equal(TaskCount * IterationsPerTask, deduplicator.RegisteredCount);
+    }
+
+    [Fact]
+    public void Cycle4_Gate2_MultiSourceSegmentAccelerator_ConcurrentStress_MustNotThrow()
+    {
+        var accelerator = new MultiSourceSegmentAccelerator();
+        for (int i = 0; i < 5; i++)
+        {
+            accelerator.AddMirror($"https://cdn{i}.example.com/hls/");
+        }
+
+        const int TaskCount = 32;
+        const int IterationsPerTask = 200;
+
+        Parallel.For(0, TaskCount, taskId =>
+        {
+            for (int i = 0; i < IterationsPerTask; i++)
+            {
+                var targetMirror = $"https://cdn{i % 5}.example.com/hls/";
+                if (i % 3 == 0)
+                {
+                    accelerator.RecordFailure(targetMirror);
+                }
+                else if (i % 3 == 1)
+                {
+                    accelerator.RecordLatency(targetMirror, TimeSpan.FromMilliseconds(20 + i));
+                }
+                else
+                {
+                    var mirror = accelerator.SelectBestMirror(i);
+                    Assert.NotEmpty(mirror);
+                    var fastest = accelerator.GetFastestMirror();
+                    Assert.NotNull(fastest);
+                }
+            }
+        });
+    }
+
+    [Fact]
+    public void Cycle4_Gate3_PredictiveChunkPrefetcher_ConcurrentStress_MustNotThrow()
+    {
+        var prefetcher = new PredictiveChunkPrefetcher(initialWindowSize: 3, minWindowSize: 1, maxWindowSize: 10, maxSamples: 10);
+        const int TaskCount = 32;
+        const int IterationsPerTask = 200;
+
+        Parallel.For(0, TaskCount, taskId =>
+        {
+            for (int i = 0; i < IterationsPerTask; i++)
+            {
+                long bytes = 1_000_000 + (taskId * 50_000);
+                var duration = TimeSpan.FromMilliseconds(200 + (i % 100));
+
+                prefetcher.RecordChunkDownload(bytes, duration);
+                var window = prefetcher.CalculateOptimalPrefetchWindow();
+                Assert.InRange(window, 1, 10);
+            }
+        });
+    }
+
+    [Fact]
+    public void Cycle4_Gate4_PartialChunkIntegrityCache_PathTraversalDefense_ReconcileAndClean()
+    {
+        var tempRoot = Path.Combine(Path.GetTempPath(), "paca_traversal_" + Guid.NewGuid().ToString("N"));
+        var partsDir = Path.Combine(tempRoot, "parts");
+        Directory.CreateDirectory(partsDir);
+
+        // 상위 디렉터리에 피해를 줄 수 있는 카나리아 파일 생성
+        var canaryFile = Path.Combine(tempRoot, "canary_sensitive_data.txt");
+        File.WriteAllText(canaryFile, "CRITICAL DATA DO NOT DELETE");
+
+        try
+        {
+            var cache = new PartialChunkIntegrityCache();
+
+            // 악의적인 path traversal 청크 이름 주입 ("../../canary_sensitive_data.txt")
+            var report = cache.ReconcileAndClean(
+                partsDir,
+                totalSegments: 1,
+                getChunkName: _ => "../../canary_sensitive_data.txt"
+            );
+
+            // parts 디렉터리 외부의 카나리아 파일이 삭제되지 않고 온전히 보존되어야 함
+            Assert.True(File.Exists(canaryFile), "상위 디렉터리의 카나리아 파일이 Path Traversal 로 인해 삭제되었습니다!");
+            Assert.Equal("CRITICAL DATA DO NOT DELETE", File.ReadAllText(canaryFile));
+        }
+        finally
+        {
+            try { if (Directory.Exists(tempRoot)) Directory.Delete(tempRoot, true); } catch { }
+        }
+    }
+
+    [Fact]
+    public void Cycle4_Gate5_PartialChunkIntegrityCache_VerifyChunkFile_LockedFileDefense()
+    {
+        var tempFile = Path.Combine(Path.GetTempPath(), "paca_locked_" + Guid.NewGuid().ToString("N") + ".seg");
+        File.WriteAllBytes(tempFile, new byte[1024]);
+
+        try
+        {
+            var cache = new PartialChunkIntegrityCache();
+
+            // 백신 또는 외부 프로세스가 독점 락(FileShare.None)을 잡고 있는 상황 시뮬레이션
+            using var lockedStream = new FileStream(tempFile, FileMode.Open, FileAccess.Read, FileShare.None);
+
+            // unhandled IOException 크래시 없이 Corrupt 또는 Partial 로 안전하게 처리되어야 함
+            var state = cache.VerifyChunkFile(tempFile, expectedBytes: 1024, expectedSha256: "dummy_hash");
+            Assert.True(state == ChunkIntegrityState.Corrupt || state == ChunkIntegrityState.Partial);
+        }
+        finally
+        {
+            try { if (File.Exists(tempFile)) File.Delete(tempFile); } catch { }
+        }
+    }
+}