Retry stalled SwiftPM artifact downloads

[cortinico]

Summary

SwiftPM artifact setup currently fails an entire CI lane when a Maven response stalls mid-body. This change:

• aborts a download after 60 seconds without body progress;
• retries transient transport errors and HTTP 408/429/5xx responses up to three total attempts with short backoff;
• keeps deterministic HTTP client errors fail-fast; and
• removes partial .download files before retrying, so a retry cannot reuse truncated content.

Changelog:

[INTERNAL] [FIXED] - Retry stalled SwiftPM artifact downloads

Diagnosis

main commit f1f516e8cb2f6c085bcc08838066b5b49c08da3b failed test_ios_spm_rntester / test (Debug) in job https://github.com/react/react-native/actions/runs/39353507614/job/118412160607. The Hermes release artifact stopped at 8.0 MB of 24.2 MB and 0 KB/s for about ten minutes before Node fetch reported terminated.

This is a transport flake rather than a deterministic source regression:

• the Release sibling on the same SHA completed successfully;
• both SwiftPM RNTester lanes passed on each of the 19 preceding main workflow runs (38/38 checks);
• the tip commit only changes Fantom SelectableParagraph rendering; and
• the exact failed artifact downloaded successfully on a subsequent probe (25,372,145 bytes in 0.29 seconds).

Because the failure is nondeterministic and independent of the commit contents, a code bisect cannot identify a meaningful introducing commit. Searches of open PRs and prior CI-monitor runs found no existing fix for this stalled-download signature. PR #59068 mentions the downloader only in its diagnosis and changes different prebuild files.

Test Plan

• node --check packages/react-native/scripts/spm/download-spm-artifacts.js
• npx -y prettier@3.9.4 --write packages/react-native/scripts/spm/download-spm-artifacts.js packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js (no changes)
• jest --runInBand packages/react-native/scripts/spm/__tests__/download-spm-artifacts-test.js — 76/76 tests passed, including transient stream retry, idle-body retry, partial-file cleanup, and fail-fast HTTP 404 coverage
• Live curl probe of the exact Hermes artifact — HTTP 200, 25,372,145 bytes

Risk and limitations

A genuinely slow transfer that makes no progress for 60 seconds is restarted, which may add up to roughly two minutes plus backoff before the final failure. The retry is bounded and final errors are still surfaced; deterministic 4xx responses are not retried. Full RNTester/Xcode CI was not reproduced locally because the failure is in remote transport rather than compilation.

[meta-codesync]

@cortinico has imported this pull request. If you are a Meta employee, you can view this in D126318143.

[react-native-bot]

This pull request was successfully merged by @cortinico in fcd141c

^{When will my fix make it into a release? | How to file a pick request?}

[meta-codesync]

@cortinico merged this pull request in fcd141c.