test_interrupted_creation[True-append] failed once in CI without aborting the upload

[laughingman7743]

Problem

tests/pyathena/filesystem/test_s3.py::TestS3File::test_interrupted_creation[True-append] failed once in CI:

• Run: https://github.com/pyathena-dev/PyAthena/actions/runs/37217440036 (attempt 1, test / run (3.14), Linux, Python 3.14.7)
• Commit: e12d5d58 (PR Move the bucket versioning request into S3Core #1098). That PR does not touch S3File or the writer path that this test exercises.
• Failure: AssertionError: Expected '_call' to be called once. Called 0 times. The assertion is the abort of the recovered multipart upload, at test_s3.py:6157.
• No log was captured. In particular, the Failed to abort multipart upload error that _close_without_commit() logs when the abort fails did not appear. So the abort was not attempted, rather than attempted and failed.

The test was added in #1085 (#1077). It sends SIGINT to the main thread while S3File._initiate_upload() waits for CreateMultipartUpload on the executor. It then checks that the creation is waited for and the upload aborted before the interrupt is re-raised.

Reproduction

Not reproduced locally (macOS, Python 3.13.1): 0 failures in 120 runs of the 10 parametrized cases, while the offline filesystem suite ran in parallel for load. The other 9 cases and all other CI runs of this test have passed.

Expected

The test passes deterministically. Either the test's signal timing is fixed, or a real window in _initiate_upload() / _close_without_commit() is fixed in which an interrupt leaves the created upload without an abort.

Proposed investigation

• Determine where the KeyboardInterrupt surfaced in the failing schedule. In particular, check whether it can be raised outside the try in _initiate_upload(), or before creation is assigned, so that _close_without_commit() runs with creation=None and finds no upload.
• Try to reproduce on Linux with Python 3.14 under load, for example in a container.
• If the window is real, fix the code, which would be a An interrupted S3File write leaves the upload behind when CreateMultipartUpload is in flight #1077 follow-up. If only the test's synchronization is wrong, fix the test.