fix(symlink): normalize subpath first component before comparing torrent name prefix

The previous fix compared subPath directly against the sanitized torrent
name, which fails when RdName contains characters removed by
RemoveInvalidPathChars (e.g. ':' on Windows). Extract and normalize the
first component of subPath before comparing so both sides go through the
same sanitization. Add tests covering the duplicate-prefix stripping case.

server/RdtClient.Service.Test/Helpers/DownloadHelperTest.cs

@@ -259,6 +259,95 @@ public class DownloadHelperTest
         Assert.Equal(expectedPath, path);
     }
 
+    [Fact]
+    public void GetDownloadPath_WithPath_WhenFilePathStartsWithTorrentName_StripsPrefix()
+    {
+        // Arrange
+        var download = new Download
+        {
+            Link = "https://fake.url/file.txt",
+            FileName = "file.txt"
+        };
+
+        String fileRelativePath;
+
+        if (OSHelper.IsLinux)
+        {
+            fileRelativePath = "Torrent Name/Saison 1/file.txt";
+        }
+        else
+        {
+            fileRelativePath = @"Torrent Name\Saison 1\file.txt";
+        }
+
+        IList<DebridClientFile> files =
+        [
+            new()
+            {
+                Path = fileRelativePath
+            }
+        ];
+
+        var torrent = new Torrent
+        {
+            RdName = "Torrent Name",
+            RdFiles = JsonSerializer.Serialize(files)
+        };
+
+        var fileSystem = new MockFileSystem();
+
+        // Act
+        var path = DownloadHelper.GetDownloadPath("/data/downloads", torrent, download, fileSystem);
+
+        // Assert
+        // The torrent name prefix in the file path should not duplicate the torrent name in the base dir
+        var expectedPath = Path.Combine("/data/downloads", "Torrent Name", "Saison 1", "file.txt");
+        Assert.Equal(expectedPath, path);
+    }
+
+    [Fact]
+    public void GetDownloadPath_WithoutPath_WhenFilePathStartsWithTorrentName_StripsPrefix()
+    {
+        // Arrange
+        var download = new Download
+        {
+            Link = "https://fake.url/file.txt",
+            FileName = "file.txt"
+        };
+
+        String fileRelativePath;
+
+        if (OSHelper.IsLinux)
+        {
+            fileRelativePath = "Torrent Name/Saison 1/file.txt";
+        }
+        else
+        {
+            fileRelativePath = @"Torrent Name\Saison 1\file.txt";
+        }
+
+        IList<DebridClientFile> files =
+        [
+            new()
+            {
+                Path = fileRelativePath
+            }
+        ];
+
+        var torrent = new Torrent
+        {
+            RdName = "Torrent Name",
+            RdFiles = JsonSerializer.Serialize(files)
+        };
+
+        // Act
+        var path = DownloadHelper.GetDownloadPath(torrent, download);
+
+        // Assert
+        var expectedPath = Path.Combine("Torrent Name", "Saison 1", "file.txt");
+        Assert.Equal(expectedPath, path);
+    }
+
     // This is probably a bug
     [Fact]
     public void GetDownloadPath_WithPath_WhenNoUriSegmentsOrFileName_ReturnsTorrentDirectory()

server/RdtClient.Service/Helpers/DownloadHelper.cs

@@ -130,17 +130,27 @@ public static class DownloadHelper
 
     private static String StripTorrentNamePrefix(String subPath, String torrentName)
     {
-        var prefix = torrentName.TrimEnd('/', '\\');
+        var separatorIndex = subPath.IndexOfAny(['/', '\\']);
 
-        if (subPath.Equals(prefix, StringComparison.OrdinalIgnoreCase))
+        String firstComponent;
+        String remainder;
+
+        if (separatorIndex < 0)
         {
-            return String.Empty;
+            firstComponent = subPath;
+            remainder = String.Empty;
+        }
+        else
+        {
+            firstComponent = subPath[..separatorIndex];
+            remainder = subPath[(separatorIndex + 1)..];
         }
 
-        if (subPath.StartsWith(prefix + "/", StringComparison.OrdinalIgnoreCase) ||
+        var normalizedFirst = RemoveInvalidPathChars(firstComponent);
-            subPath.StartsWith(prefix + "\\", StringComparison.OrdinalIgnoreCase))
+
+        if (normalizedFirst.Equals(torrentName.TrimEnd('/', '\\'), StringComparison.OrdinalIgnoreCase))
         {
-            return subPath[(prefix.Length + 1)..];
+            return remainder;
         }
 
         return subPath;