fix(task): handle agent assignment and empty JSON output

[wufengwind]

Prevent self.agent from being set to None before the guard check, which would break subsequent retries or replay.

Also fix falsy check on json_output to use 'is not None' so that empty dict {} is preserved as valid output.

Summary by CodeRabbit

• Bug Fixes
  • Fixed validation timing for agent assignment to ensure proper error handling when no agent is configured
  • Improved JSON output file serialization to correctly handle and preserve empty JSON objects during task execution

[corridor-security]

Summary: This PR adjusts task execution state handling and preserves empty JSON outputs when writing task results; no exploitable security vulnerabilities were identified.

Risk: Low risk. The changes do not introduce new public endpoints, authentication or authorization logic, external integrations, or unsafe handling of untrusted input.

[coderabbitai]

📝 Walkthrough

Walkthrough

Two behavioral fixes are applied symmetrically to Task._aexecute_core and Task._execute_core in task.py: the missing-agent validation is reordered to raise before self.agent = agent executes, and the output file branch switches from a truthiness check to an explicit json_output is not None comparison.

Changes

Task execution fixes

Layer / File(s)	Summary
Agent validation before assignment (async + sync) lib/crewai/src/crewai/task.py	In both _aexecute_core (line 648) and _execute_core (line 773), the guard raising on a missing agent is moved before self.agent = agent, preventing the assignment from occurring when validation fails.
Output file: json_output is not None check (async + sync) lib/crewai/src/crewai/task.py	In both _aexecute_core (line 743) and _execute_core (line 868), the condition selecting saved output file content changes from if json_output to if json_output is not None, so an empty-dict JSON result is written as JSON rather than falling back to the pydantic/result serialization path.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title directly summarizes both main changes: agent assignment handling and JSON output validation fixes.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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