fix(upload): harden fetch upload streams

[sjinks]

Summary

• replaces upload progress PassThrough/data listeners with Transform streams that count bytes while forwarding them to undici.fetch
• removes the unsupported Expect header before dispatching requests through undici.fetch
• preserves useful low-level fetch cause details when fetchWithRetry exhausts retries
• adds regression coverage for:
  • single-PUT uploads streaming exactly Content-Length bytes
  • TypeError: fetch failed with an underlying write ECONNRESET cause
  • incoming Expect: 100-continue headers

Why

Follow-up from PLTFRM-2491 / the custom deploy incident thread. After v4.0.7, the customer no longer sees the disturbed-stream or missing-duplex errors, but later debug traces exposed two more local undici failure modes:

[cause]: NotSupportedError: expect header not supported
code: 'UND_ERR_NOT_SUPPORTED'

and on the single-PUT path:

[cause]: RequestContentLengthMismatchError: Request body length does not match content-length header
code: 'UND_ERR_REQ_CONTENT_LENGTH_MISMATCH'

undici.fetch cannot send the Expect header, so leaving that header in presigned options guarantees a local failure before the request reaches S3.

For the content-length mismatch, the upload body was piped through a PassThrough with a data listener for progress. That can put the stream into flowing mode before undici attaches its reader, allowing progress accounting to consume bytes that are no longer delivered to fetch. Using a Transform keeps progress accounting in the same stream pipeline as the upload body and preserves backpressure/byte delivery.

If future retries still exhaust with a lower-level transport cause, the final error becomes more actionable, e.g. fetch failed: write ECONNRESET, without including presigned URLs or other request details.

Testing

• npm run jest -- __tests__/lib/client-file-uploader.js __tests__/lib/fetch-with-retry-undici.js --runInBand (ran all non-e2e suites: 56 passed / 593 tests)
• npm run check-types
• npm run cmd:lint -- src/lib/client-file-uploader.ts __tests__/lib/client-file-uploader.js
• npm run build

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues or OpenSSF Scorecard issues found.

Scanned Files

None

[Copilot]

Pull request overview

This PR improves the error surfaced when fetchWithRetry exhausts retries by preserving low-level Undici fetch failure details (via the underlying cause) while still avoiding request/presigned URL details. It also adds regression coverage to ensure the new error message and cause chain are maintained.

Changes:

• Wrap the final exhausted-retries error to append an underlying cause message (when present) and preserve the original error as cause.
• Add a Jest regression test covering TypeError: fetch failed with an underlying write ECONNRESET cause.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/lib/client-file-uploader.ts	Adds withCauseMessage() and uses it when retries are exhausted to preserve actionable fetch cause details.
tests/lib/client-file-uploader.js	Adds regression test ensuring the final error message includes the underlying cause and preserves the original error via cause.

[rinatkhaziev]

:intensifies-more:

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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