fix: root at s3 upload part copy

[ferhatelmas]

What kind of change does this PR introduce?

Bug fix

What is the current behavior?

S3 upload part copy response doesn't set root tag name correct.

What is the new behavior?

It sets now and regression test validates the wire.
SDK doesn't care about root tag but might not be compatible with strict clients.

Additional context

S3 docs

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[coveralls]

Coverage Report for CI Build 29779999775

Coverage remained the same at 79.556%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	12754
Covered Lines:	10595
Line Coverage:	83.07%
Relevant Branches:	7448
Covered Branches:	5477
Branch Coverage:	73.54%
Branches in Coverage %:	Yes
Coverage Strength:	426.81 hits per line

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💛 - Coveralls

[claude]

LGTM. Simple, correct fix that wraps the UploadPartCopy response in the CopyPartResult root element, matching the S3 API spec and the pattern already used elsewhere in this file (e.g. copyObject -> CopyObjectResult).

Extended reasoning...

Overview

This PR touches a single method (uploadPartCopy) in src/storage/protocols/s3/s3-handler.ts, changing the shape of the responseBody returned to the XML serializer so the wire response is wrapped in a CopyPartResult root tag instead of emitting bare ETag/LastModified fields. The test file was updated to issue a raw signed HTTP request and assert on the actual XML text (root tag name, presence of <ETag>/<LastModified>, closing tag), rather than relying on the AWS SDK's lenient parsing, which previously masked the missing root element.

Security risks

None. This is a pure response-shape fix with no changes to auth, input parsing, or data access. The values being serialized (ETag, LastModified) are already computed upstream and unchanged.

Level of scrutiny

Low. This is a narrowly scoped, mechanical fix aligning one endpoint's response format with the S3 API spec and with sibling methods in the same file that already follow this root-tag convention (CopyObjectResult, ListPartsResult, InitiateMultipartUploadResult, etc). The change is a straightforward object-nesting edit plus a regression test that directly exercises the wire format, giving good confidence the fix is correct.

Other factors

No CODEOWNER-restricted or auth/crypto-sensitive code is touched. The updated test is a meaningful improvement since it now validates the actual XML rather than the SDK's parsed representation.