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

tests/Paca.Tests/Core/SubtitleAndNetworkResilienceExtremeRedTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Threading.Tasks;
+using Paca.Core;
+using Paca.Core.Net;
+using Xunit;
+
+namespace Paca.Tests.Core;
+
+public class SubtitleAndNetworkResilienceExtremeRedTests
+{
+    [Fact]
+    public void SubtitleBurnInEngine_InPlaceOverwrite_ThrowsArgumentException()
+    {
+        var ex = Assert.Throws<ArgumentException>(() =>
+            SubtitleBurnInEngine.BuildBurnInCommandLine("movie.mp4", "sub.srt", "movie.mp4"));
+        Assert.Contains("identical", ex.Message, StringComparison.OrdinalIgnoreCase);
+    }
+
+    [Theory]
+    [InlineData(null, "sub.srt", "out.mp4")]
+    [InlineData("", "sub.srt", "out.mp4")]
+    [InlineData("in.mp4", null, "out.mp4")]
+    [InlineData("in.mp4", "", "out.mp4")]
+    [InlineData("in.mp4", "sub.srt", null)]
+    [InlineData("in.mp4", "sub.srt", "")]
+    public void SubtitleBurnInEngine_NullOrEmptyPaths_ThrowsArgumentException(string? inVid, string? sub, string? outVid)
+    {
+        Assert.Throws<ArgumentException>(() =>
+            SubtitleBurnInEngine.BuildBurnInCommandLine(inVid!, sub!, outVid!));
+    }
+
+    [Fact]
+    public void SubtitleBurnInEngine_EscapePath_EscapesSquareBrackets()
+    {
+        var path = @"C:\Downloads\[SubsPlease] Video [1080p].srt";
+        var escaped = SubtitleBurnInEngine.EscapeSubtitlePathForFfmpeg(path);
+
+        Assert.Contains(@"\[", escaped);
+        Assert.Contains(@"\]", escaped);
+    }
+
+    [Fact]
+    public void SubtitleBurnInEngine_FontNameInjection_Sanitized()
+    {
+        var style = new SubtitleBurnInStyle
+        {
+            FontName = "Arial,Bold;drop=all",
+            FontSize = 24
+        };
+        var forceStyle = SubtitleBurnInEngine.BuildForceStyleString(style);
+
+        Assert.DoesNotContain("Arial,Bold", forceStyle);
+        Assert.DoesNotContain(";", forceStyle);
+    }
+
+    [Theory]
+    [InlineData(0)]
+    [InlineData(-5)]
+    public void SubtitleBurnInEngine_InvalidFontSize_ThrowsArgumentOutOfRangeException(int invalidSize)
+    {
+        var style = new SubtitleBurnInStyle { FontSize = invalidSize };
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            SubtitleBurnInEngine.BuildForceStyleString(style));
+    }
+
+    [Theory]
+    [InlineData("https://i.4cdn.org/wsg/1234567.webm", 1200)]
+    [InlineData("http://is2.4chan.org/pol/src/123.jpg", 1200)]
+    [InlineData("i.4cdn.org:443", 1200)]
+    [InlineData("https://v.redd.it/xyz987/DASH_720.mp4", 800)]
+    [InlineData("reddit.com:80", 800)]
+    [InlineData("https://example.com/video.mp4", 200)]
+    public void HostRateLimiter_FullUrlAndPort_NormalizesAndRecognizesDomain(string input, int expectedInterval)
+    {
+        var interval = HostRateLimiter.GetDefaultIntervalMs(input);
+        Assert.Equal(expectedInterval, interval);
+    }
+
+    [Fact]
+    public async Task MultiCdnMeshDownloader_NullMirrorList_ReturnsFailureGracefully()
+    {
+        var downloader = new MultiCdnMeshDownloader();
+        var result = await downloader.RaceDownloadSegmentAsync(null!);
+        Assert.False(result.IsSuccess);
+    }
+
+    [Fact]
+    public async Task MultiCdnMeshDownloader_RelativeUri_DoesNotThrowInvalidOperationException()
+    {
+        var downloader = new MultiCdnMeshDownloader();
+        var mirrors = new List<Uri> { new("/relative/path/seg0.ts", UriKind.Relative) };
+
+        var ex = await Record.ExceptionAsync(() => downloader.RaceDownloadSegmentAsync(mirrors));
+        Assert.Null(ex);
+    }
+
+    [Fact]
+    public async Task MultiCdnMeshDownloader_NegativeStagger_DoesNotThrow()
+    {
+        var downloader = new MultiCdnMeshDownloader();
+        var mirrors = new List<Uri>
+        {
+            new("https://cdn1.example.com/seg0.ts"),
+            new("https://cdn2.example.com/seg0.ts")
+        };
+
+        var ex = await Record.ExceptionAsync(() => downloader.RaceDownloadSegmentAsync(mirrors, staggerDelayMs: -50));
+        Assert.Null(ex);
+    }
+}