Fix double-encoded JSON in Plan JSON display

Parse nested plan_json field before displaying to avoid escaped newlines.

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

server.py

@@ -1589,7 +1589,14 @@ async def run_plan_visualization(run_id: str, request: Request):
     '''
 
     # Add collapsible Plan JSON section
-    plan_json_str = json.dumps(plan_data, indent=2)
+    # Parse nested plan_json if present (it's double-encoded as a string)
+    display_plan = plan_data.copy()
+    if "plan_json" in display_plan and isinstance(display_plan["plan_json"], str):
+        try:
+            display_plan["plan_json"] = json.loads(display_plan["plan_json"])
+        except json.JSONDecodeError:
+            pass
+    plan_json_str = json.dumps(display_plan, indent=2)
     # Escape HTML entities in JSON
     plan_json_str = plan_json_str.replace("&", "&amp;").replace("<", "&lt;").replace(">", "&gt;")
     content += f'''