fix: preserve math through streaming HTML repair

Disable only Remend's incomplete-HTML stripping in message/tool content and reasoning rendering. Keep TeX, source data, and sanitization unchanged; unfinished HTML can display literally.

PR #266 identified the less-than comparison trigger. This uses an independently authored renderer configuration fix rather than its TeX-spacing workaround, with streaming, incremental, literal-code, and safety regressions.

components/ai-elements/message.tsx

@@ -355,6 +355,12 @@ export const streamdownPlugins = {
   math: createMathPlugin({ singleDollarTextMath: true }),
 } as unknown as PluginConfig;
 
+// Remend's incomplete-HTML heuristic mistakes `<b` in `$a<b$` for a
+// partial tag and deletes the remaining source before math can tokenize.
+// Preserve that text (unfinished prose HTML may show literally); Streamdown's
+// separate sanitization/hardening and all other Markdown repairs stay enabled.
+export const streamdownRemend = { htmlTags: false };
+
 export const MessageResponse = memo(
   ({ className, children, ...props }: MessageResponseProps) => {
     // Legacy backslash delimiters are converted in a single linear scan;
@@ -375,6 +381,7 @@ export const MessageResponse = memo(
         )}
         components={mdComponents}
         plugins={streamdownPlugins}
+        remend={streamdownRemend}
         {...props}
       >
         {content}