fix: ToolMessage contained an incorrect error message when all search engines returned empty results

[minturtle]

Features

• Fixed a bug where Manus Agent using the browser_use tool’s web_search action crashes with list index out of range when all configured search engines (Google / DuckDuckGo / Baidu / Bing) return empty results (results: []).
• Added a guard before accessing first_search_result in web_search_tool to validate the result list length and, when empty, return a meaningful error message instead of raising an index error.
• Improved the error propagation so that Manus Agent can treat this situation as “search failed / no results”, instead of misinterpreting it as an internal tool failure and repeatedly issuing the same query.

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Feature Docs

• No documentation changes are required. This PR only improves runtime error handling and error messages for edge cases in web search.

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Influence

• For normal scenarios where at least one search engine returns results, behavior remains unchanged.

• In edge cases where all search engines return empty results (e.g., due to being blocked by a captcha while still returning HTTP 200 and HTML content):

  • The list index out of range exception no longer occurs.
  • The tool now returns an explicit “no search results from any engine” error message, which is surfaced as a tool_message.
  • This reduces the chance that Manus Agent will interpret the situation as an internal failure and aggressively retry the same query.

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Result

• i used gpt-oss-120b.

• Reproduced an environment where all engines return results: [] (captcha on Bing in my case) and verified:

  • Before the fix:

    • Error: Browser action 'web_search' failed: list index out of range is raised.
    • The error string is injected into tool_message, and Manus Agent then appears to re-issue the same query multiple times.

2025-11-21 14:02:06.065 | INFO     | app.agent.toolcall:think:89 - 🔧 Tool arguments: {"action": "web_search", "query": "2025 AI agent news site:arxiv.org"}
2025-11-21 14:02:06.066 | INFO     | app.agent.toolcall:execute_tool:180 - 🔧 Activating tool: 'browser_use'...
2025-11-21 14:02:06.067 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Google...
2025-11-21 14:02:06.672 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Duckduckgo...
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+news+site%3Aarxiv.org 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+news+site%3Aarxiv.org&first=11&FORM=PERE 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+news+site%3Aarxiv.org&first=21&FORM=PERE1 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+news+site%3Aarxiv.org&first=31&FORM=PERE2 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+news+site%3Aarxiv.org&first=41&FORM=PERE3 200
2025-11-21 14:02:10.246 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Baidu...
2025-11-21 14:02:11.626 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Bing...
2025-11-21 14:02:12.137 | WARNING  | app.tool.web_search:execute:274 - All search engines failed. Waiting 10 seconds before retry 1/3...

• After 3 retries, the following log appears:

Error: Browser action 'web_search' failed: list index out of range

• The ToolMessage content then contains:

Observed output of cmd `browser_use` executed:\nError: Browser action 'web_search' failed: list index out of range

• After this, Manus Agent runs web_search again with the same (or very similar) query:

2025-11-21 14:06:06.049 | INFO     | app.agent.toolcall:think:89 - 🔧 Tool arguments: {"action": "web_search", "query": "2025 AI agent site:arxiv.org"}
2025-11-21 14:06:06.051 | INFO     | app.agent.toolcall:execute_tool:180 - 🔧 Activating tool: 'browser_use'...
2025-11-21 14:06:06.052 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Google...
2025-11-21 14:06:06.705 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Duckduckgo...
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+site%3Aarxiv.org 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+site%3Aarxiv.org&first=11&FORM=PERE 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+site%3Aarxiv.org&first=21&FORM=PERE1 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+site%3Aarxiv.org&first=31&FORM=PERE2 200
INFO     [primp] response: https://www.bing.com/search?q=2025+AI+agent+site%3Aarxiv.org&first=41&FORM=PERE3 200
2025-11-21 14:06:10.682 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Baidu...
2025-11-21 14:06:11.838 | INFO     | app.tool.web_search:_try_all_engines:299 - 🔎 Attempting search with Bing...
2025-11-21 14:06:12.021 | WARNING  | app.tool.web_search:execute:274 - All search engines failed. Waiting 10 seconds before retry 1/3...

• After the fix:

  • No index error is raised.
  • A clear “all search engines returned no results” error is propagated via tool_message.
  • Manus Agent no longer treats this as an internal crash of browser_use, and the repeated same-query behavior is mitigated.