feat(ui): add external links extension to markdown rendering

Add custom markdown extension to automatically set external links in reports to open in new tabs with security attributes.

app/app.py

@@ -1,10 +1,12 @@
 from __future__ import annotations
 
 import asyncio
-import time
-
-import markdown
-import reflex as rx
+import time
+
+import markdown
+from markdown.extensions import Extension
+from markdown.treeprocessors import Treeprocessor
+import reflex as rx
 
 from .research_assistant import environment_status, run_research_assistant
 
@@ -15,17 +17,30 @@ PANEL_PADDING = {"initial": "1rem", "sm": "1.25rem"}
 _RUNNING_TASKS: dict[str, asyncio.Task] = {}
 
 
-def _plain_markdown(value) -> str:
+def _plain_markdown(value) -> str:
     if isinstance(value, str):
         return value
     if isinstance(value, dict):
         nested = value.get("markdown_report")
         return nested if isinstance(nested, str) else str(nested or value)
     nested = getattr(value, "markdown_report", None)
-    return nested if isinstance(nested, str) else str(value)
-
-
-class State(rx.State):
+    return nested if isinstance(nested, str) else str(value)
+
+
+class ExternalLinksTreeprocessor(Treeprocessor):
+    def run(self, root):
+        for element in root.iter("a"):
+            element.set("target", "_blank")
+            element.set("rel", "noopener noreferrer")
+        return root
+
+
+class ExternalLinksExtension(Extension):
+    def extendMarkdown(self, md):
+        md.treeprocessors.register(ExternalLinksTreeprocessor(md), "external_links", 15)
+
+
+class State(rx.State):
     query: str = ""
     logs: list[str] = []
     report_markdown: str = ""
@@ -112,11 +127,11 @@ class State(rx.State):
             report, trace_url = await run_research_assistant(query, progress=self._log)
             async with self:
                 self.report_markdown = _plain_markdown(report.markdown_report)
-                self.report_html = markdown.markdown(
-                    self.report_markdown,
-                    extensions=["extra", "sane_lists", "tables"],
-                    output_format="html5",
-                )
+                self.report_html = markdown.markdown(
+                    self.report_markdown,
+                    extensions=["extra", "sane_lists", "tables", ExternalLinksExtension()],
+                    output_format="html5",
+                )
                 self.trace_url = trace_url
                 self.status = "Complete"
         except asyncio.CancelledError: