fix: URL-encode search query and detect empty results as failure (fixes #274)

- Use urllib.parse.urlencode to properly encode the POST body, so queries
  containing special characters like '&', '+', '=' are sent correctly
- Extend execution_failure_check to also detect "No search results" as a
  failure, preventing the agent from silently looping when all SearXNG
  engines are rate-limited and return no results

sources/tools/searxSearch.py

@@ -1,6 +1,7 @@
 import requests
 from bs4 import BeautifulSoup
 import os
+from urllib.parse import urlencode
 
 if __name__ == "__main__": # if running as a script for individual testing
     sys.path.append(os.path.dirname(os.path.dirname(os.path.dirname(os.path.abspath(__file__)))))
@@ -77,7 +78,14 @@ class searxSearch(Tools):
             'Upgrade-Insecure-Requests': '1',
             'User-Agent': self.user_agent
         }
-        data = f"q={query}&categories=general&language=auto&time_range=&safesearch=0&theme=simple".encode('utf-8')
+        data = urlencode({
+            'q': query,
+            'categories': 'general',
+            'language': 'auto',
+            'time_range': '',
+            'safesearch': '0',
+            'theme': 'simple'
+        }).encode('utf-8')
         try:
             response = requests.post(search_url, headers=headers, data=data, verify=False)
             response.raise_for_status()
@@ -101,7 +109,7 @@ class searxSearch(Tools):
         """
         Checks if the execution failed based on the output.
         """
-        return "Error" in output
+        return "Error" in output or "No search results" in output
 
     def interpreter_feedback(self, output: str) -> str:
         """