fix/line-number-wrongly-copied (#11857)

* fix(code-viewer): copy selected code without line numbers

* fix(context-menu): strip line numbers from code selection

* style(codeviewer): fix format

* fix: preserve indentation and format when copying mixed content (text + code blocks)

- Replace regex-based extraction with DOM structure-based approach
- Remove line number elements while preserving all other content
- Use TreeWalker to handle mixed content (text paragraphs + code blocks)
- Preserve indentation and newlines in code blocks
- Simplify CodeViewer.tsx by removing duplicate context menu logic

Fixes #11790

* style: remove unused comment

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* refactor: optimize TreeWalker performance

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

src/renderer/src/components/ContextMenu/index.tsx

@@ -6,6 +6,61 @@ interface ContextMenuProps {
   children: React.ReactNode
 }
 
+/**
+ * Extract text content from selection, filtering out line numbers in code viewers.
+ * Preserves all content including plain text and code blocks, only removing line numbers.
+ * This ensures right-click copy in code blocks doesn't include line numbers while preserving indentation.
+ */
+function extractSelectedText(selection: Selection): string {
+  // Validate selection
+  if (selection.rangeCount === 0 || selection.isCollapsed) {
+    return ''
+  }
+
+  const range = selection.getRangeAt(0)
+  const fragment = range.cloneContents()
+
+  // Check if the selection contains code viewer elements
+  const hasLineNumbers = fragment.querySelectorAll('.line-number').length > 0
+
+  // If no line numbers, return the original text (preserves formatting)
+  if (!hasLineNumbers) {
+    return selection.toString()
+  }
+
+  // Remove all line number elements
+  fragment.querySelectorAll('.line-number').forEach((el) => el.remove())
+
+  // Handle all content using optimized TreeWalker with precise node filtering
+  // This approach handles mixed content correctly while improving performance
+  const walker = document.createTreeWalker(fragment, NodeFilter.SHOW_TEXT | NodeFilter.SHOW_ELEMENT, null)
+
+  let result = ''
+  let node = walker.nextNode()
+
+  while (node) {
+    if (node.nodeType === Node.TEXT_NODE) {
+      // Preserve text content including whitespace
+      result += node.textContent
+    } else if (node.nodeType === Node.ELEMENT_NODE) {
+      const element = node as Element
+
+      // Add newline after block elements and code lines to preserve structure
+      if (['H1', 'H2', 'H3', 'H4', 'H5', 'H6'].includes(element.tagName)) {
+        result += '\n'
+      } else if (element.classList.contains('line')) {
+        // Add newline after code lines to preserve code structure
+        result += '\n'
+      }
+    }
+
+    node = walker.nextNode()
+  }
+
+  // Clean up excessive newlines but preserve code structure
+  return result.trim()
+}
+
 // FIXME: Why does this component name look like a generic component but is not customizable at all?
 const ContextMenu: React.FC<ContextMenuProps> = ({ children }) => {
   const { t } = useTranslation()
@@ -45,8 +100,12 @@ const ContextMenu: React.FC<ContextMenuProps> = ({ children }) => {
 
   const onOpenChange = (open: boolean) => {
     if (open) {
-      const selectedText = window.getSelection()?.toString()
-      setSelectedText(selectedText)
+      const selection = window.getSelection()
+      if (!selection || selection.rangeCount === 0 || selection.isCollapsed) {
+        setSelectedText(undefined)
+        return
+      }
+      setSelectedText(extractSelectedText(selection) || undefined)
     }
   }