[Bug] Fix batch finalization for existing temp uploads

[cursor]

Pull Request Description

Fixes a batch data-loss bug where jobs that already had multipart temp output IDs skipped finalize_job_output_data() in the scheduler execute_job() path. Those jobs could be marked finalized without completing multipart uploads or assembling final output/error files.

Bug and impact:

• Worker-loaded / resumed jobs can enter execution with temp_output_file_id and temp_error_file_id already set.
• execute_job() used that as a reason to skip both preparation and final aggregation.
• When such a job reached FINALIZING, it could be marked FINALIZED while final output objects remained incomplete/missing, causing broken downloads and lost batch results.

Root cause:

• A single has_temp_files guard was used for two different lifecycle steps: skip output preparation, and skip output finalization.

Fix:

• Keep skipping preparation when temp file IDs already exist.
• Always run finalize_job_output_data() when a job reaches FINALIZING.
• Add a regression test covering an IN_PROGRESS job with existing temp IDs to ensure preparation is not rerun but finalization is invoked before marking done.

Validation performed:

• PYTHONPATH=/workspace/python/aibrix python3 -m pytest tests/batch/test_driver.py::test_execute_job_finalizes_job_with_existing_temp_files tests/batch/test_driver.py::test_batch_driver_resuming
• PYTHONPATH=/workspace/python/aibrix python3 -m pytest tests/batch/test_driver.py

Related Issues

Resolves: #

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