Fix argument list mutation in summarize()

[abhu85]

Summary

Fixes #10121

The summarize() function in scripts/performance/benchmark_utils.py mutates the argument list when calling the subprocess for JSON output. This is done using list.extend() which modifies the original list in place.

Problem

The function constructs summarize_args and reuses it for both subprocess calls:

with open(os.path.join(summary_dir, 'summary.txt'), 'wb') as f:
    subprocess.check_call(summarize_args, stdout=f)
with open(os.path.join(summary_dir, 'summary.json'), 'wb') as f:
    summarize_args.extend(['--output-format', 'json'])  # Mutation!
    subprocess.check_call(summarize_args, stdout=f)

While this doesn't cause immediate issues in the current implementation (since summarize_args is a local variable), it violates best practices for CLI argument construction and could cause subtle bugs if the code is refactored.

Solution

Use list concatenation instead of mutation to create a fresh list for the JSON output call:

with open(os.path.join(summary_dir, 'summary.json'), 'wb') as f:
    json_args = summarize_args + ['--output-format', 'json']
    subprocess.check_call(json_args, stdout=f)

Testing

• Added unit tests in tests/unit/test_benchmark_utils.py
• Tests verify that the argument list is not mutated between subprocess calls
• All existing unit tests pass (2777 passed)

$ python -m pytest tests/unit/test_benchmark_utils.py -v
tests/unit/test_benchmark_utils.py::TestSummarize::test_summarize_does_not_mutate_args PASSED
tests/unit/test_benchmark_utils.py::TestSummarize::test_summarize_multiple_calls_are_independent PASSED

Co-Authored-By: Claude Opus 4.6 noreply@anthropic.com