Harden clipboard writes against "clipboard in use" failures

.github/CLAUDE.md

@@ -334,4 +334,100 @@ To update this file, ensure that all sections are kept current with the latest a
 - Add new sections as needed for significant changes in the project structure or processes.
 - Ensure all technical terms are explained or linked to relevant documentation.
 - Periodically review for outdated information and remove or update as necessary.
-- If told to not do something, ensure this is also added to the "Dont Do that" section.
+- If told to not do something, ensure this is also added to the "Dont Do that" section.
+
+# Karpathy Guidelines
+
+Behavioral guidelines to reduce common LLM coding mistakes.
+
+**Tradeoff:** These guidelines bias toward caution over speed. For trivial tasks, use judgment.
+
+## 1. Clarify Before Executing
+
+**Resolve ambiguity up front — before spawning agents or starting any autonomous work.**
+
+Do this in order, then stop and ask before proceeding:
+
+1. **Understand the request.** Read what was asked closely and state your assumptions explicitly.
+2. **Inspect the codebase.** Check the relevant code, conventions, and existing patterns. Note anything that's unclear or that could be interpreted in more than one way.
+3. **Ask.** Raise every consequential question now, batched together — don't pick an interpretation silently, and don't defer the question into the work itself.
+
+Throughout:
+
+- If multiple interpretations exist, present them — don't choose one silently.
+- If a simpler approach exists, say so. Push back when warranted.
+- Don't invent APIs. Confirm a function, flag, or endpoint exists — and check its signature — before calling it. If you can't verify it, say so rather than guessing.
+
+Only once these questions are resolved do you move to execution (§4).
+
+## 2. Simplicity First
+
+**Minimum code that solves the problem. Nothing speculative.**
+
+- No features beyond what was asked.
+- No abstractions for single-use code.
+- No "flexibility" or "configurability" that wasn't requested.
+- No error handling for impossible scenarios.
+- If you write 200 lines and it could be 50, rewrite it.
+
+Ask yourself: "Would a senior engineer say this is overcomplicated?" If yes, simplify.
+
+## 3. Surgical Changes
+
+**Touch only what you must. Clean up only your own mess.**
+
+When editing existing code:
+
+- Don't "improve" adjacent code, comments, or formatting.
+- Don't refactor things that aren't broken.
+- Match existing style, even if you'd do it differently.
+- If you spot problems outside your task — dead code, bugs — mention them; don't fix or delete them unless asked.
+
+When your changes create orphans:
+
+- Remove imports/variables/functions that YOUR changes made unused.
+- Don't remove pre-existing dead code unless asked.
+
+The test: every changed line should trace directly to the user's request.
+
+## 4. Goal-Driven Execution
+
+**Define success criteria. Loop until verified.**
+
+Begin only once §1's questions are resolved. Then turn the task into a verifiable goal with an observable check. A passing test is the strongest check; a clean typecheck, running it and inspecting output, or diffing against expected output also count.
+
+- "Add validation" → "Write tests for invalid inputs, then make them pass"
+- "Fix the bug" → "Write a test that reproduces it, then make it pass"
+- "Refactor X" → "Ensure tests pass before and after"
+- "Update the config" → "Apply it, start the service, and confirm the setting takes effect"
+
+For multi-step tasks, state a brief plan:
+
+```
+1. [Step] → verify: [check]
+2. [Step] → verify: [check]
+3. [Step] → verify: [check]
+```
+
+When no obvious check exists (docs, exploration, some one-off scripts), ask how to verify success before starting. Don't report success you haven't actually observed.
+
+Strong, agreed-upon criteria — settled in §1 — let you loop independently. Weak criteria ("make it work") force constant clarification, which is why §1 comes first.
+
+## 5. Delegate Grunt Work Down a Tier
+
+**Spend the capable model on judgment; push mechanical, low-context work to a cheaper model.**
+
+Act as an orchestrator. Fan out grunt work — reading files, gathering context, simple searches, minor mechanical edits, other simple tool calls — to cheaper agents, then review their findings and any code changes yourself before acting on them. Keep the important and dangerous work — architecture, ambiguous decisions, risky or hard-to-reverse edits, final review — on the more capable model.
+
+Which tier to spawn depends on who you are:
+
+- **If you are Fable 5**, spawn Opus 4.8 agents for grunt work that still needs some capability; for genuinely simple tasks, hand off directly to Sonnet 5 instead. Review what they return.
+- **If you are Opus 4.8**, and a task needs little knowledge or context, fan out to Sonnet 5 agents and review what they return.
+
+Match the model to the task: pick the cheapest tier that can do the job well, and skip an intermediate tier when the work is simple enough for a lower one.
+
+Guidelines:
+
+- Only delegate work that is genuinely low-context and low-risk. If doing it well requires the capable model's judgment, keep it.
+- Give each agent a self-contained task with clear success criteria (per §4) so you can verify its output without redoing the work.
+- Never merge a delegated finding or edit unblocked — review it first. The cheaper model did the legwork; you own the decision.

src/LogExpert.Resources/Resources.de.resx

@@ -188,6 +188,9 @@
   <data name="Folder_open" type="System.Resources.ResXFileRef, System.Windows.Forms">
     <value>images\png\48\Folder_open.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a</value>
   </data>
+  <data name="LogExpert_Common_UI_Message_ClipboardInUse" xml:space="preserve">
+    <value>Kopieren in die Zwischenablage nicht möglich. Sie wird von einer anderen Anwendung verwendet. Bitte versuchen Sie es erneut.</value>
+  </data>
   <data name="LogExpert_Common_UI_Title_LogExpert" xml:space="preserve">
 		<value>LogExpert</value>
 	</data>

src/LogExpert.Resources/Resources.resx

@@ -188,6 +188,9 @@
   <data name="Folder_open" type="System.Resources.ResXFileRef, System.Windows.Forms">
     <value>images\png\48\Folder_open.png;System.Drawing.Bitmap, System.Drawing, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a</value>
   </data>
+  <data name="LogExpert_Common_UI_Message_ClipboardInUse" xml:space="preserve">
+    <value>Could not copy to the clipboard. It is in use by another application. Please try again.</value>
+  </data>
   <data name="LogExpert_Common_UI_Title_LogExpert" xml:space="preserve">
         <value>LogExpert</value>
         <comment>LogExpert</comment>

src/LogExpert.Resources/Resources.zh-CN.resx

@@ -117,6 +117,9 @@
   <resheader name="writer">
     <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
   </resheader>
+  <data name="LogExpert_Common_UI_Message_ClipboardInUse" xml:space="preserve">
+    <value>无法复制到剪贴板。剪贴板正被其他应用程序使用，请重试。</value>
+  </data>
   <data name="LogExpert_Common_UI_Title_LogExpert" xml:space="preserve">
     <value>LogExpert</value>
     <comment>LogExpert</comment>

src/LogExpert.Tests/Extensions/ClipboardHelperTests.cs

@@ -0,0 +1,117 @@
+using LogExpert.UI.Extensions;
+
+using NUnit.Framework;
+
+using Vanara.PInvoke;
+
+namespace LogExpert.Tests.Extensions;
+
+/// <summary>
+/// Tests for the hardened clipboard writes (see issue with "Requested Clipboard operation
+/// did not succeed" / ExternalException, previously reported in #195). When another
+/// application holds the clipboard open, LogExpert must report failure instead of crashing.
+/// </summary>
+[TestFixture]
+[Apartment(ApartmentState.STA)]
+[NonParallelizable]
+[System.Diagnostics.CodeAnalysis.SuppressMessage("Globalization", "CA1303:Do not pass literals as localized parameters", Justification = "Unit Tests")]
+public class ClipboardHelperTests
+{
+    [Test]
+    public void TrySetText_ClipboardAvailable_PlacesTextAndReturnsTrue ()
+    {
+        var ok = ClipboardHelper.TrySetText("LogExpert clipboard test");
+
+        Assert.That(ok, Is.True);
+        Assert.That(GetClipboardTextWithRetry(), Is.EqualTo("LogExpert clipboard test"));
+    }
+
+    /// <summary>
+    /// Reads the clipboard text, retrying briefly. Clipboard managers and similar tools
+    /// open the clipboard to inspect new content right after it changes, which can make an
+    /// immediate read-back fail or come up empty even though the write succeeded.
+    /// </summary>
+    private static string GetClipboardTextWithRetry ()
+    {
+        for (var i = 0; i < 20; i++)
+        {
+            var text = Clipboard.GetText();
+            if (!string.IsNullOrEmpty(text))
+            {
+                return text;
+            }
+
+            Thread.Sleep(100);
+        }
+
+        return string.Empty;
+    }
+
+    [Test]
+    public void TrySetText_ClipboardHeldByAnotherWindow_ReturnsFalseInsteadOfThrowing ()
+    {
+        using ClipboardLock clipboardLock = new();
+
+        var ok = ClipboardHelper.TrySetText("some text");
+
+        Assert.That(ok, Is.False);
+    }
+
+    [Test]
+    public void TrySetDataObject_ClipboardAvailable_PlacesDataAndReturnsTrue ()
+    {
+        var ok = ClipboardHelper.TrySetDataObject("LogExpert data object test");
+
+        Assert.That(ok, Is.True);
+        Assert.That(GetClipboardTextWithRetry(), Is.EqualTo("LogExpert data object test"));
+    }
+
+    [Test]
+    public void TrySetDataObject_ClipboardHeldByAnotherWindow_ReturnsFalseInsteadOfThrowing ()
+    {
+        using ClipboardLock clipboardLock = new();
+
+        var ok = ClipboardHelper.TrySetDataObject("some data");
+
+        Assert.That(ok, Is.False);
+    }
+
+    /// <summary>
+    /// Holds the Win32 clipboard open from a background thread (without closing it),
+    /// which makes every clipboard access in other threads/processes fail — the same
+    /// situation an external clipboard-monitoring tool causes.
+    /// </summary>
+    private sealed class ClipboardLock : IDisposable
+    {
+        private readonly Thread _thread;
+        private readonly ManualResetEventSlim _acquired = new(false);
+        private readonly ManualResetEventSlim _release = new(false);
+
+        public ClipboardLock ()
+        {
+            _thread = new Thread(() =>
+            {
+                if (!User32.OpenClipboard(HWND.NULL))
+                {
+                    throw new InvalidOperationException("Test setup failed: could not open the clipboard");
+                }
+
+                _acquired.Set();
+                _release.Wait();
+                _ = User32.CloseClipboard();
+            })
+            {
+                IsBackground = true
+            };
+
+            _thread.Start();
+            _ = _acquired.Wait(TimeSpan.FromSeconds(5));
+        }
+
+        public void Dispose ()
+        {
+            _release.Set();
+            _ = _thread.Join(TimeSpan.FromSeconds(5));
+        }
+    }
+}

src/LogExpert.UI/Controls/LogWindow/LogWindow.cs

@@ -1967,9 +1967,9 @@ private void OnEditModeCopyToolStripMenuItemClick (object sender, EventArgs e)
     {
         if (dataGridView.EditingControl is DataGridViewTextBoxEditingControl ctl)
         {
-            if (!string.IsNullOrEmpty(ctl.SelectedText))
+            if (!string.IsNullOrEmpty(ctl.SelectedText) && !ClipboardHelper.TrySetText(ctl.SelectedText))
             {
-                Clipboard.SetText(ctl.SelectedText);
+                StatusLineError(Resources.LogExpert_Common_UI_Message_ClipboardInUse);
             }
         }
     }
@@ -5370,7 +5370,10 @@ private void CopyMarkedLinesToClipboard ()
                 data = new DataObject(DataFormats.UnicodeText, transformed);
             }
 
-            Clipboard.SetDataObject(data);
+            if (!ClipboardHelper.TrySetDataObject(data))
+            {
+                StatusLineError(Resources.LogExpert_Common_UI_Message_ClipboardInUse);
+            }
         }
         else
         {
@@ -5412,7 +5415,10 @@ private void CopyMarkedLinesToClipboard ()
                 }
             }
 
-            Clipboard.SetDataObject(clipText.ToString());
+            if (!ClipboardHelper.TrySetDataObject(clipText.ToString()))
+            {
+                StatusLineError(Resources.LogExpert_Common_UI_Message_ClipboardInUse);
+            }
         }
     }
 

src/LogExpert.UI/Dialogs/ExceptionWindow.cs

@@ -1,5 +1,7 @@
 using System.Runtime.Versioning;
 
+using LogExpert.UI.Extensions;
+
 namespace LogExpert.UI.Dialogs;
 
 [SupportedOSPlatform("windows")]
@@ -28,7 +30,7 @@ public ExceptionWindow (string errorText, string stackTrace)
         _errorText = errorText;
         _stackTrace = stackTrace;
 
-        stackTraceTextBox.Text = _errorText + @"\n\n" + _stackTrace;
+        stackTraceTextBox.Text = _errorText + Environment.NewLine + Environment.NewLine + _stackTrace;
         stackTraceTextBox.Select(0, 0);
 
         ResumeLayout();
@@ -51,7 +53,8 @@ private void ApplyResources ()
 
     private void CopyToClipboard ()
     {
-        Clipboard.SetText(_errorText + @"\n\n" + _stackTrace);
+        // Never let a failed clipboard access escalate out of the error dialog itself
+        _ = ClipboardHelper.TrySetText(_errorText + Environment.NewLine + Environment.NewLine + _stackTrace);
     }
 
     #endregion

src/LogExpert.UI/Dialogs/LogTabWindow/LogTabWindow.cs

@@ -2417,8 +2417,15 @@ private void OnToolStripButtonBubblesClick (object sender, EventArgs e)
     [SupportedOSPlatform("windows")]
     private void OnCopyPathToClipboardToolStripMenuItemClick (object sender, EventArgs e)
     {
-        var logWindow = dockPanel.ActiveContent as LogWindow.LogWindow;
-        Clipboard.SetText(logWindow.Title);
+        if (dockPanel.ActiveContent is not LogWindow.LogWindow logWindow)
+        {
+            return;
+        }
+
+        if (!ClipboardHelper.TrySetText(logWindow.Title))
+        {
+            _ = MessageBox.Show(this, Resources.LogExpert_Common_UI_Message_ClipboardInUse, Resources.LogExpert_Common_UI_Title_LogExpert, MessageBoxButtons.OK, MessageBoxIcon.Warning);
+        }
     }
 
     private void OnFindInExplorerToolStripMenuItemClick (object sender, EventArgs e)

src/LogExpert.UI/Dialogs/PluginHashDialog.cs

@@ -1,7 +1,8 @@
 using System.Globalization;
-using System.Runtime.InteropServices;
 using System.Runtime.Versioning;
 
+using LogExpert.UI.Extensions;
+
 namespace LogExpert.UI.Dialogs;
 
 [SupportedOSPlatform("windows")]
@@ -55,25 +56,17 @@ private void ApplyResources (string pluginName)
 
     private void OnButtonCopyClick (object sender, EventArgs e)
     {
-        try
-        {
-            Clipboard.SetText(_hash);
-            _ = MessageBox.Show(
+        _ = ClipboardHelper.TrySetText(_hash)
+            ? MessageBox.Show(
                 Resources.PluginHashDialog_UI_Message_CopySuccess,
                 Resources.PluginHashDialog_UI_Message_SuccessTitle,
                 MessageBoxButtons.OK,
-                MessageBoxIcon.Information);
-        }
-        catch (Exception ex) when (ex is ExternalException or
-                                         ThreadStateException or
-                                         ThreadStateException)
-        {
-            _ = MessageBox.Show(
-                string.Format(CultureInfo.InvariantCulture, Resources.PluginHashDialog_UI_Message_CopyError, ex.Message),
+                MessageBoxIcon.Information)
+            : MessageBox.Show(
+                string.Format(CultureInfo.InvariantCulture, Resources.PluginHashDialog_UI_Message_CopyError, Resources.LogExpert_Common_UI_Message_ClipboardInUse),
                 Resources.PluginHashDialog_UI_Message_ErrorTitle,
                 MessageBoxButtons.OK,
                 MessageBoxIcon.Error);
-        }
     }
 
     private void OnButtonCloseClick (object sender, EventArgs e)