Clamp selection text bounds

src/XTerm.NET.Tests/SelectionTests.cs

@@ -68,6 +68,32 @@ public void SelectAll_IncludesScrollback_NotJustViewport()
         Assert.Contains("Line7", selectedText);
     }
 
+    [Fact]
+    public void SelectionText_ClampsNegativeColumns()
+    {
+        var terminal = new Terminal(new TerminalOptions { Rows = 3, Cols = 10, Scrollback = 20 });
+        terminal.Write("alpha");
+
+        terminal.Selection.StartSelection(-3, 0);
+        terminal.Selection.UpdateSelection(4, 0);
+        terminal.Selection.EndSelection();
+
+        Assert.Equal("alpha", terminal.Selection.GetSelectionText());
+    }
+
+    [Fact]
+    public void SelectionText_ClampsColumnsPastRightEdge()
+    {
+        var terminal = new Terminal(new TerminalOptions { Rows = 3, Cols = 10, Scrollback = 20 });
+        terminal.Write("alpha");
+
+        terminal.Selection.StartSelection(0, 0);
+        terminal.Selection.UpdateSelection(30, 0);
+        terminal.Selection.EndSelection();
+
+        Assert.StartsWith("alpha", terminal.Selection.GetSelectionText());
+    }
+
     [Fact]
     public void Selection_IsCleared_WhenTrimRemovesSelectedLines()
     {

src/XTerm.NET/Selection/SelectionManager.cs

@@ -145,8 +145,11 @@ public string GetSelectionText()
             if (line == null)
                 continue;
 
-            int startX = (y == start.y) ? start.x : 0;
-            int endX = (y == end.y) ? end.x : _terminal.Cols - 1;
+            int startX = Math.Clamp((y == start.y) ? start.x : 0, 0, _terminal.Cols - 1);
+            int endX = Math.Clamp((y == end.y) ? end.x : _terminal.Cols - 1, 0, _terminal.Cols - 1);
+
+            if (startX > endX)
+                continue;
 
             var lineText = line.TranslateToString(false, startX, endX + 1);
             text.Append(lineText);