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

tests/Paca.Tests/Platform/PlatformMediaToolsExtremeRedTests.cs

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+using System;
+using System.Collections.Generic;
+using System.Threading;
+using System.Threading.Tasks;
+using Paca.Core.Platform;
+using Xunit;
+
+namespace Paca.Tests.Platform;
+
+public class PlatformMediaToolsExtremeRedTests
+{
+    // ==========================================
+    // 1. ChapterSplitter
+    // ==========================================
+
+    [Fact]
+    public void ChapterSplitter_GenerateFfmetadata_NullChapters_ReturnsValidHeaderWithoutCrashing()
+    {
+        var meta = ChapterSplitter.GenerateFfmetadata(null!);
+        Assert.NotNull(meta);
+        Assert.Contains(";FFMETADATA1", meta);
+    }
+
+    [Fact]
+    public void ChapterSplitter_GenerateFfmetadata_ListContainingNullChapter_SkipsNullChapter()
+    {
+        var chapters = new List<ChapterInfo>
+        {
+            null!,
+            new(1, "Intro", 0.0, 30.0),
+            null!
+        };
+
+        var meta = ChapterSplitter.GenerateFfmetadata(chapters);
+        Assert.NotNull(meta);
+        Assert.Contains("title=Intro", meta);
+    }
+
+    [Fact]
+    public void ChapterSplitter_GetChapterFileName_NullTitle_ReturnsSafeDefault()
+    {
+        var name = ChapterSplitter.GetChapterFileName(1, null!, "mp4");
+        Assert.NotNull(name);
+        Assert.StartsWith("01_", name);
+        Assert.EndsWith(".mp4", name);
+    }
+
+    // ==========================================
+    // 2. LosslessSmartTrimmer
+    // ==========================================
+
+    [Theory]
+    [InlineData(double.NaN)]
+    [InlineData(double.NegativeInfinity)]
+    [InlineData(double.PositiveInfinity)]
+    public void LosslessSmartTrimmer_FindNearestKeyframe_InvalidTargetSec_ReturnsDefault(double target)
+    {
+        var keyframes = new[] { 0.0, 5.0, 10.0, 15.0 };
+        var nearest = LosslessSmartTrimmer.FindNearestKeyframe(keyframes, target);
+        Assert.False(double.IsNaN(nearest));
+        Assert.False(double.IsInfinity(nearest));
+    }
+
+    [Fact]
+    public void LosslessSmartTrimmer_FindNearestKeyframe_KeyframesWithNaNOrNegatives_FiltersCorrectly()
+    {
+        var keyframes = new[] { double.NaN, -10.0, 5.0, 10.0 };
+        var nearest = LosslessSmartTrimmer.FindNearestKeyframe(keyframes, 6.0);
+        Assert.Equal(5.0, nearest);
+    }
+
+    [Fact]
+    public async Task LosslessSmartTrimmer_TrimLosslessAsync_NaNTimestamps_ThrowsArgumentException()
+    {
+        var trimmer = new LosslessSmartTrimmer(DesktopProcessRunner.Default);
+        await Assert.ThrowsAsync<ArgumentException>(() =>
+            trimmer.TrimLosslessAsync("ffmpeg.exe", "in.mp4", "out.mp4", double.NaN, 10.0, CancellationToken.None));
+    }
+
+    // ==========================================
+    // 3. VideoWatermarkBurner
+    // ==========================================
+
+    [Fact]
+    public void VideoWatermarkBurner_BuildDrawTextFilter_NullText_DoesNotThrow()
+    {
+        var filter = VideoWatermarkBurner.BuildDrawTextFilter(null!);
+        Assert.NotNull(filter);
+        Assert.Contains("drawtext=", filter);
+    }
+
+    [Fact]
+    public void VideoWatermarkBurner_BuildDrawTextFilter_TextWithNewlines_EscapedOrStripped()
+    {
+        var filter = VideoWatermarkBurner.BuildDrawTextFilter("Line 1\r\nLine 2\nLine 3");
+        Assert.NotNull(filter);
+        Assert.DoesNotContain("\r", filter);
+        Assert.DoesNotContain("\n", filter);
+    }
+
+    [Theory]
+    [InlineData(-0.1)]
+    [InlineData(1.1)]
+    [InlineData(double.NaN)]
+    public void VideoWatermarkBurner_BuildOverlayFilter_InvalidOpacity_ThrowsArgumentOutOfRangeException(double opacity)
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() =>
+            VideoWatermarkBurner.BuildOverlayFilter(WatermarkPosition.Center, opacity: opacity));
+    }
+}