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fix(cuga-lite): handle exception in find_tools when shortlister LLM fails #67

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fix(cuga-lite): handle exception in find_tools when shortlister LLM fails #67

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6a4a08d
fix: handle OutputParserException in find_tools when shortlister LLM …
haroldship Mar 17, 2026
c391ad6
fix: sanitize log output and bound fallback tool list size
haroldship Mar 19, 2026
be91744
fix: guard fallback doc extraction against exceptions
haroldship Mar 19, 2026
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77 changes: 68 additions & 9 deletions src/cuga/backend/cuga_graph/nodes/cuga_lite/prompt_utils.py
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Original file line number Diff line number Diff line change
Expand Up @@ -252,15 +252,23 @@ async def find_tools(
llm_manager = LLMManager()
model = llm or llm_manager.get_model(settings.agent.code.model)
chain = BaseAgent.get_chain(prompt, model, ShortListerOutputLite)
response = await chain.ainvoke(
{
"input": query,
"all_apps": apps_as_dict,
"all_tools": tools_as_dict,
"instructions": "",
"memory": None,
}
)
try:
response = await chain.ainvoke(
{
"input": query,
"all_apps": apps_as_dict,
"all_tools": tools_as_dict,
"instructions": "",
"memory": None,
}
)
except Exception as e:
logger.bind(
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@sami-marreed sami-marreed Mar 19, 2026

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What is the reason this could fail here?

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@haroldship haroldship Mar 20, 2026

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The reason it failed for OP was that the shortlister returned None and the JSON Decoder threw an OutputParserException. This is passed through to here, where this code will catch it and any other excpeptions. This is a sample stack trace:

Error during execution: OutputParserException('Invalid json output: \nFor troubleshooting, visit: https://docs.langchain.com/oss/python/langchain/errors/OUTPUT_PARSING_FAILURE ')
Traceback (most recent call last):
  File "/root/proj/cuga-internal-evaluation/.venv/lib/python3.13/site-packages/langchain_core/output_parsers/json.py", line 84, in parse_result
    return parse_json_markdown(text)
  File "/root/proj/cuga-internal-evaluation/.venv/lib/python3.13/site-packages/langchain_core/utils/json.py", line 164, in parse_json_markdown
    return _parse_json(json_str, parser=parser)
  File "/root/proj/cuga-internal-evaluation/.venv/lib/python3.13/site-packages/langchain_core/utils/json.py", line 194, in _parse_json
    return parser(json_str)
  File "/root/proj/cuga-internal-evaluation/.venv/lib/python3.13/site-packages/langchain_core/utils/json.py", line 137, in parse_partial_json
    return json.loads(s, strict=strict)
           ~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/json/__init__.py", line 365, in loads
    return cls(**kw).decode(s)
           ~~~~~~~~~~~~~~~~^^^
  File "/root/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/json/decoder.py", line 345, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/json/decoder.py", line 363, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/root/proj/cuga-internal-evaluation/vendor/cuga-agent/src/cuga/backend/cuga_graph/nodes/cuga_lite/executors/code_executor.py", line 121, in eval_with_tools_async
    result = await executor.execute(
             ^^^^^^^^^^^^^^^^^^^^^^^
    ...<3 lines>...
    )
    ^
  File "/root/proj/cuga-internal-evaluation/vendor/cuga-agent/src/cuga/backend/cuga_graph/nodes/cuga_lite/executors/local/local_executor.py", line 80, in execute
    result_locals = await asyncio.wait_for(async_main(), timeout=timeout)
                    ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/.local/share/uv/python/cpython-3.13.12-linux-x86_64-gnu/lib/python3.13/asyncio/tasks.py", line 507, in wait_for
    return await fut
           ^^^^^^^^^
  File "<string>", line 5, in _async_main
  File "/root/proj/cuga-internal-evaluation/vendor/cuga-agent/src/cuga/backend/cuga_graph/nodes/cuga_lite/cuga_lite_graph.py", line 121, in wrapper_with_pydantic
    result = await func(*args, **kwargs) if inspect.iscoroutinefunction(func) else func(*args, **kwargs)
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/root/proj/cuga-internal-evaluation/vendor/cuga-agent/src/cuga/backend/cuga_graph/nodes/cuga_lite/cuga_lite_graph.py", line 375, in find_tools_func
    return await PromptUtils.find_tools(
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        query=query, all_tools=filtered_tools, all_apps=filtered_apps, llm=llm

query_len=len(query),
error_type=type(e).__name__,
).opt(exception=True).warning("Tool shortlisting failed; using fallback tool list")
# Return all tools unfiltered so the agent can still proceed
return PromptUtils._format_all_tools_as_fallback(all_tools)

enriched_tools = []
for api_detail in response.result:
Expand Down Expand Up @@ -364,6 +372,57 @@ async def find_tools(

return "\n".join(markdown_lines)

@staticmethod
def _format_all_tools_as_fallback(all_tools: List[StructuredTool]) -> str:
"""Format all tools as a fallback when shortlisting fails.

Returns a markdown string listing all available tools so the agent can still proceed.
Output is bounded to prevent context-overflow failures.
"""
if not all_tools:
return "No matching tools found for your query."

max_tools = 20
max_doc_chars = 1200
shown_tools = all_tools[:max_tools]

markdown_lines = [
f"# Available Tools ({len(all_tools)} total)\n",
"**Note:** Tool shortlisting was unavailable. Showing all tools.\n",
]
if len(all_tools) > max_tools:
markdown_lines.append(
f"**Output truncated:** showing first {max_tools} of {len(all_tools)} tools.\n"
)

for idx, tool in enumerate(shown_tools, 1):
markdown_lines.append(f"## {idx}. `{tool.name}`\n")
if hasattr(tool, 'description') and tool.description:
markdown_lines.append(f"**Description:** {tool.description}\n")

try:
params_doc, response_doc = PromptUtils.get_tool_docs(tool)
except Exception:
logger.bind(
tool_name=getattr(tool, "name", "<unknown>"),
).opt(exception=True).warning("Tool doc extraction failed during fallback; skipping docs")
params_doc, response_doc = "", ""
if params_doc:
if len(params_doc) > max_doc_chars:
params_doc = params_doc[:max_doc_chars] + "\n... (truncated)"
markdown_lines.append("**Parameters:**\n")
markdown_lines.append(f"{params_doc}\n")

if response_doc:
if len(response_doc) > max_doc_chars:
response_doc = response_doc[:max_doc_chars] + "\n... (truncated)"
markdown_lines.append("**Response Schema:**\n")
markdown_lines.append(f"{response_doc}\n")

markdown_lines.append("---\n")

return "\n".join(markdown_lines)

@staticmethod
def create_find_tools_bound(all_tools: List[StructuredTool], all_apps: List[AppDefinition]):
"""Create a bound version of find_tools with all_tools and all_apps pre-bound.
Expand Down
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