Address review feedback: width cap, thread safety, initial height, docs

- Add MAX_RENDER_WIDTH (4096) upper bound to prevent OOM from absurd widths
- Wrap env var set/restore in a static lock for thread safety
- Use initial height of 1 instead of width for first layout pass
- Fix XML docs to clarify ShowCopyButtons is always disabled for ANSI output

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: tig

Terminal.Gui/Views/Markdown/MarkdownView.Ansi.cs

@@ -5,6 +5,9 @@ namespace Terminal.Gui.Views;
 
 public partial class Markdown
 {
+    private const int MAX_RENDER_WIDTH = 4096;
+    private static readonly Lock _renderToAnsiLock = new ();
+
     /// <summary>
     ///     Renders the current <see cref="Text"/> (or the supplied <paramref name="markdown"/>)
     ///     to an ANSI escape-sequence string suitable for writing directly to a terminal.
@@ -13,7 +16,8 @@ public partial class Markdown
     ///     Optional markdown text to render. If <see langword="null"/>, uses the current <see cref="Text"/>.
     /// </param>
     /// <param name="width">
-    ///     The target column width for word-wrapping. Defaults to 80.
+    ///     The target column width for word-wrapping. Defaults to 80. Clamped to
+    ///     the range [<see cref="MIN_WRAP_WIDTH"/>, 4096].
     /// </param>
     /// <returns>A string containing ANSI escape sequences that reproduce the styled markdown output.</returns>
     /// <remarks>
@@ -24,9 +28,10 @@ public partial class Markdown
     ///     </para>
     ///     <para>
     ///         Configuration properties set on this instance — <see cref="SyntaxHighlighter"/>,
-    ///         <see cref="MarkdownPipeline"/>, <see cref="UseThemeBackground"/>,
-    ///         <see cref="ShowHeadingPrefix"/>, and <see cref="ShowCopyButtons"/> — are copied to the
-    ///         temporary view used for rendering.
+    ///         <see cref="MarkdownPipeline"/>, <see cref="UseThemeBackground"/>, and
+    ///         <see cref="ShowHeadingPrefix"/> — are copied to the temporary view used for rendering.
+    ///         Copy buttons (<see cref="ShowCopyButtons"/>) are always disabled for ANSI output because
+    ///         they are interactive-only controls.
     ///     </para>
     /// </remarks>
     public string RenderToAnsi (string? markdown = null, int width = 80)
@@ -35,6 +40,10 @@ public string RenderToAnsi (string? markdown = null, int width = 80)
         {
             width = MIN_WRAP_WIDTH;
         }
+        else if (width > MAX_RENDER_WIDTH)
+        {
+            width = MAX_RENDER_WIDTH;
+        }
 
         string text = markdown ?? Text;
 
@@ -43,50 +52,56 @@ public string RenderToAnsi (string? markdown = null, int width = 80)
             return string.Empty;
         }
 
-        // Suppress real terminal I/O for the headless driver
-        string? previousValue = Environment.GetEnvironmentVariable ("DisableRealDriverIO");
-        Environment.SetEnvironmentVariable ("DisableRealDriverIO", "1");
-
-        try
+        // A static lock guards the process-wide DisableRealDriverIO environment variable
+        // so concurrent calls do not race on set/restore.
+        lock (_renderToAnsiLock)
         {
-            using IApplication app = Application.Create ().Init (DriverRegistry.Names.ANSI);
-            app.Driver!.SetScreenSize (width, width);
+            string? previousValue = Environment.GetEnvironmentVariable ("DisableRealDriverIO");
+            Environment.SetEnvironmentVariable ("DisableRealDriverIO", "1");
 
-            using Markdown renderView = new ()
+            try
             {
-                Text = text,
-                Width = Dim.Fill (),
-                Height = Dim.Fill (),
-                SyntaxHighlighter = SyntaxHighlighter,
-                MarkdownPipeline = MarkdownPipeline,
-                UseThemeBackground = UseThemeBackground,
-                ShowHeadingPrefix = ShowHeadingPrefix,
-                ShowCopyButtons = false // Copy buttons are interactive-only
-            };
+                using IApplication app = Application.Create ().Init (DriverRegistry.Names.ANSI);
 
-            renderView.App = app;
-            renderView.SetRelativeLayout (app.Screen.Size);
-            renderView.Layout ();
+                // Use a small initial height for the first layout pass (just enough to compute content height)
+                app.Driver!.SetScreenSize (width, 1);
 
-            int contentHeight = renderView.GetContentHeight ();
+                using Markdown renderView = new ()
+                {
+                    Text = text,
+                    Width = Dim.Fill (),
+                    Height = Dim.Fill (),
+                    SyntaxHighlighter = SyntaxHighlighter,
+                    MarkdownPipeline = MarkdownPipeline,
+                    UseThemeBackground = UseThemeBackground,
+                    ShowHeadingPrefix = ShowHeadingPrefix,
+                    ShowCopyButtons = false // Copy buttons are interactive-only
+                };
 
-            if (contentHeight < 1)
-            {
-                return string.Empty;
-            }
+                renderView.App = app;
+                renderView.SetRelativeLayout (app.Screen.Size);
+                renderView.Layout ();
 
-            // Resize to the full content height so the entire document is drawn
-            app.Driver.SetScreenSize (width, contentHeight);
-            renderView.Frame = app.Screen with { X = 0, Y = 0 };
-            renderView.Layout ();
-            app.Driver.ClearContents ();
-            renderView.Draw ();
+                int contentHeight = renderView.GetContentHeight ();
 
-            return app.Driver.ToAnsi ();
-        }
-        finally
-        {
-            Environment.SetEnvironmentVariable ("DisableRealDriverIO", previousValue);
+                if (contentHeight < 1)
+                {
+                    return string.Empty;
+                }
+
+                // Resize to the full content height so the entire document is drawn
+                app.Driver.SetScreenSize (width, contentHeight);
+                renderView.Frame = app.Screen with { X = 0, Y = 0 };
+                renderView.Layout ();
+                app.Driver.ClearContents ();
+                renderView.Draw ();
+
+                return app.Driver.ToAnsi ();
+            }
+            finally
+            {
+                Environment.SetEnvironmentVariable ("DisableRealDriverIO", previousValue);
+            }
         }
     }
 }