[NA] [SDK] fix: retry transient S3 attachment failures

[harsh181018]

Details

Retry transient S3 multipart attachment failures caused by remote protocol disconnects and HTTP 502, 503, and 504 responses. The S3 retry path now uses bounded jittered exponential backoff and re-raises the original failure after retry exhaustion, matching the resilience already present in the regular REST client.

Change checklist

• User facing
• Documentation update

Issues

• Resolves Python SDK: retry transient S3 attachment upload disconnects and gateway errors #8135

AI-WATERMARK

AI-WATERMARK: yes

• If yes:
  • Tools: OpenAI Codex
  • Model(s): GPT-5
  • Scope: Investigation, implementation, unit tests, and PR drafting
  • Human verification: Pending; this draft PR is ready for author and maintainer review.

Testing

• PATH="$PWD/sdks/python/venv/bin:$PATH" make precommit
• cd sdks/python && venv/bin/python -m pytest -q tests/unit/test_s3_httpx_client.py tests/unit/file_upload/s3_multipart_upload/test_s3_file_uploader.py
• Validated successful retry after httpx.RemoteProtocolError and HTTP 500/502/503/504 responses.
• Validated that HTTP 403 is not retried.
• Environment: macOS, Python 3.13.11.
• End-to-end tests were not run because this is an isolated Python SDK retry-policy change covered by unit tests.

Documentation

No documentation changes are needed; this updates internal retry behavior without changing the public API.