refactor(web): improve theme style element management in useHighlightTheme hook

web/frontend/src/hooks/use-highlight-theme.ts

@@ -4,14 +4,39 @@ import githubDarkCss from "highlight.js/styles/github-dark.css?inline"
 import githubLightCss from "highlight.js/styles/github.css?inline"
 
 const THEME_STYLE_ID = "hljs-theme-style"
+const THEME_STYLE_OWNER_ATTR = "data-picoclaw-highlight-theme"
+const THEME_STYLE_OWNER_VALUE = "true"
+const MANAGED_THEME_STYLE_SELECTOR = `style[${THEME_STYLE_OWNER_ATTR}="${THEME_STYLE_OWNER_VALUE}"]`
+const ID_THEME_STYLE_SELECTOR = `style#${THEME_STYLE_ID}`
 
-function getOrCreateThemeStyleElement() {
-  let styleElement = document.getElementById(THEME_STYLE_ID)
-  if (!styleElement) {
-    styleElement = document.createElement("style")
-    styleElement.id = THEME_STYLE_ID
-    document.head.appendChild(styleElement)
+function getOrCreateThemeStyleElement(): HTMLStyleElement {
+  const managedStyleElement = document.head.querySelector<HTMLStyleElement>(
+    MANAGED_THEME_STYLE_SELECTOR,
+  )
+  if (managedStyleElement) {
+    return managedStyleElement
   }
+
+  const existingStyleElement =
+    document.querySelector<HTMLStyleElement>(ID_THEME_STYLE_SELECTOR)
+  if (existingStyleElement) {
+    existingStyleElement.setAttribute(
+      THEME_STYLE_OWNER_ATTR,
+      THEME_STYLE_OWNER_VALUE,
+    )
+    return existingStyleElement
+  }
+
+  const conflictingElement = document.getElementById(THEME_STYLE_ID)
+  const styleElement = document.createElement("style")
+  if (!conflictingElement) {
+    styleElement.id = THEME_STYLE_ID
+  }
+
+  // Leave conflicting non-style nodes untouched and track the injected style explicitly.
+  styleElement.setAttribute(THEME_STYLE_OWNER_ATTR, THEME_STYLE_OWNER_VALUE)
+  document.head.appendChild(styleElement)
+
   return styleElement
 }