Fix format_answer() to re-raise OutputParserError for retry logic (Issue #3771)

[devin-ai-integration]

Fix format_answer() to re-raise OutputParserError for retry logic (Issue #3771)

Summary

This PR fixes a bug where format_answer() was catching all exceptions including OutputParserError and converting them to AgentFinish, which prevented the retry logic in _invoke_loop() from working correctly when LLMs return malformed output.

The Problem:
When an LLM returns malformed output (e.g., missing colons after "Thought", "Action", "Action Input"), the agent should retry with an error message. However, format_answer() was catching the OutputParserError and immediately returning an AgentFinish, bypassing the retry mechanism in crew_agent_executor.py:250-257.

The Fix:
Modified format_answer() to specifically catch and re-raise OutputParserError, allowing it to bubble up to the retry logic in _invoke_loop(). The generic Exception handler is preserved as a fallback for truly unexpected errors.

Changes:

• Updated lib/crewai/src/crewai/utilities/agent_utils.py to re-raise OutputParserError
• Added comprehensive unit tests in lib/crewai/tests/utilities/test_agent_utils.py
• All 51 related tests (parser + agent_utils) pass

Review & Testing Checklist for Human

This is a yellow risk change (small, targeted fix with good unit test coverage, but limited end-to-end testing):

• End-to-end verification: Test with an actual agent that receives malformed LLM output (missing colons in Thought/Action/Action Input). Verify the agent retries with error messages instead of immediately returning the malformed text
• Full test suite: Run the complete test suite to ensure no regressions (I ran parser and agent_utils tests successfully, but not the full suite due to an unrelated qdrant import error)
• Exception handling review: Verify that the generic Exception catch → AgentFinish fallback is the correct behavior for unexpected errors

Test Plan

To manually verify the fix works end-to-end:

1. Create a simple agent with a task
2. Mock or inject a malformed LLM response (e.g., "Thought\nThe user wants X.\nAction\nSome Tool\nAction Input:\n{...}")
3. Verify the agent logs show retry attempts with error messages like "Invalid Format: I missed the ':' after 'Action:'"
4. Verify the agent doesn't immediately finish with the malformed text

Notes

• Requested by João ([email protected]) via Slack
• Session: https://app.devin.ai/sessions/486c0800c45747258d2c6b6085e8243f
• Issue [BUG] format_answer() catches OutputParserException, breaking retry logic for malformed LLM outputs #3771 includes the exact malformed output format to test with
• The fix is surgical (5 lines changed) and well-tested at the unit level, but end-to-end verification is recommended

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