Fix #4509: Strip markdown code-block fences from LLM JSON responses in Converter

[devin-ai-integration]

Fix #4509: Strip markdown code-block fences from LLM JSON responses

Summary

Some LLMs wrap their JSON responses in markdown code-block fences (```json ... ```), which causes model_validate_json() to fail with a Pydantic validation error. This manifests as "Failed to add to long term memory" errors when memory is enabled.

The fix adds a _strip_markdown_fences() helper that removes these delimiters before JSON parsing, applied in three locations within converter.py:

• Converter.to_pydantic() — function-calling path
• Converter.to_pydantic() — non-function-calling path
• convert_to_model() — before json.loads()

Additionally, the function-calling path now has a handle_partial_json() fallback (previously only present in the non-function-calling path), and the except clauses now catch ValueError alongside ValidationError since model_validate_json can raise either.

11 new unit tests cover the helper function, both converter paths, the TaskEvaluation model, and convert_to_model.

Review & Testing Checklist for Human

• Regex edge cases: The fence pattern requires a \n before the closing ```. Verify this matches all real-world LLM outputs (e.g., some models may omit the trailing newline before closing fences).
• Fallback chain in function-calling path: When handle_partial_json is called with agent=None and regex extraction fails, it will fall through to convert_with_instructions() which raises TypeError. This is caught by the outer retry loop, but the error message could be confusing. Consider whether this needs a cleaner error path.
• Widened except clause: (ValidationError, ValueError) — confirm no legitimate errors are being silently swallowed that should propagate.
• End-to-end verification: Run the reproduction script from the issue with memory=True against a real LLM that wraps JSON in markdown fences, and confirm long-term memory saves succeed without errors.
• Unused import: Entity is imported but unused in test_converter_to_pydantic_strips_fences_multiline_no_function_calling.

Notes

• Requested by: João
• Link to Devin run

[devin-ai-integration]

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