Fix double HTML encoding in /diff view

PolyPilot.Tests/DiffParserTests.cs

@@ -144,4 +144,49 @@ public void Parse_MultipleFiles_ParsesAll()
         Assert.Equal("a.cs", files[0].FileName);
         Assert.Equal("b.cs", files[1].FileName);
     }
+
+    [Fact]
+    public void Parse_SpecialHtmlCharacters_PreservedInContent()
+    {
+        // Verify the parser preserves raw HTML characters as-is.
+        // DiffView relies on Blazor's @() auto-encoding, so the parser
+        // must never pre-encode content.
+        var diff = """
+            diff --git a/template.html b/template.html
+            --- a/template.html
+            +++ b/template.html
+            @@ -1,3 +1,3 @@
+             <div class="container">
+            -    <span title="old">old &amp; value</span>
+            +    <span title="new">new &amp; value</span>
+             </div>
+            """;
+        var files = DiffParser.Parse(diff);
+        var lines = files[0].Hunks[0].Lines;
+
+        // Parser must pass through <, >, ", & verbatim — DiffView's @() handles encoding
+        Assert.Equal("<div class=\"container\">", lines[0].Content);
+        Assert.Equal("    <span title=\"old\">old &amp; value</span>", lines[1].Content);
+        Assert.Equal("    <span title=\"new\">new &amp; value</span>", lines[2].Content);
+        Assert.Equal("</div>", lines[3].Content);
+    }
+
+    [Fact]
+    public void Parse_AngleBracketsInCode_NotEncoded()
+    {
+        // Verify generic type parameters with <> are preserved as-is
+        var diff = """
+            diff --git a/f.cs b/f.cs
+            --- a/f.cs
+            +++ b/f.cs
+            @@ -1,2 +1,2 @@
+            -List<string> items = new List<string>();
+            +Dictionary<string, int> items = new Dictionary<string, int>();
+            """;
+        var files = DiffParser.Parse(diff);
+        var lines = files[0].Hunks[0].Lines;
+
+        Assert.Equal("List<string> items = new List<string>();", lines[0].Content);
+        Assert.Equal("Dictionary<string, int> items = new Dictionary<string, int>();", lines[1].Content);
+    }
 }

PolyPilot/Components/DiffView.razor

@@ -1,5 +1,4 @@
 @using PolyPilot.Models
-@using System.Web
 
 @if (Files.Count == 0)
 {
@@ -48,9 +47,9 @@ else
                                 {
                                     <tr>
                                         <td class="diff-ln @(row.Left?.Type == DiffLineType.Removed ? "ln-del" : "")">@(row.Left?.OldLineNo?.ToString() ?? "")</td>
-                                        <td class="diff-code @(row.Left == null ? "diff-blank" : row.Left.Type == DiffLineType.Removed ? "diff-del" : "diff-ctx")"><pre>@(row.Left != null ? HtmlEncode(row.Left.Content) : "")</pre></td>
+                                        <td class="diff-code @(row.Left == null ? "diff-blank" : row.Left.Type == DiffLineType.Removed ? "diff-del" : "diff-ctx")"><pre>@(row.Left?.Content ?? "")</pre></td>
                                         <td class="diff-ln @(row.Right?.Type == DiffLineType.Added ? "ln-add" : "")">@(row.Right?.NewLineNo?.ToString() ?? "")</td>
-                                        <td class="diff-code @(row.Right == null ? "diff-blank" : row.Right.Type == DiffLineType.Added ? "diff-add" : "diff-ctx")"><pre>@(row.Right != null ? HtmlEncode(row.Right.Content) : "")</pre></td>
+                                        <td class="diff-code @(row.Right == null ? "diff-blank" : row.Right.Type == DiffLineType.Added ? "diff-add" : "diff-ctx")"><pre>@(row.Right?.Content ?? "")</pre></td>
                                     </tr>
                                 }
                             }
@@ -70,7 +69,4 @@ else
     {
         Files = DiffParser.Parse(RawDiff);
     }
-
-    private static string HtmlEncode(string s) =>
-        System.Web.HttpUtility.HtmlEncode(s);
 }

PolyPilot/Models/DiffParser.cs

@@ -1,5 +1,4 @@
 using System.Text;
-using System.Web;
 
 namespace PolyPilot.Models;