fix(worker): avoid shared err race in multipart upload

[mesutoezdil]

TL;DR

In multipartUpload, every part-upload goroutine wrote the shared function-scope
err instead of a goroutine-local one. Concurrent parts raced on err
(go test -race flags it), and a failing part whose err was overwritten to nil
by a peer could skip its error return and dereference a nil upload result,
panicking the worker on the large-response upload path. Extract the per-part
upload into uploadPart, keeping the error and result local to each call.

Issues

Closes #442

Testing

go test ./worker/ -race passes. Added TestUploadPart covering success,
failure (returns the error with no nil dereference), and a concurrent run where
one part fails and must not clobber the others. Verified the pre-fix shared-err
pattern reports a data race under -race. No QA needed.

Checklist

• I am familiar with the Contributing Guidelines.
• I have signed off my commits for Developer Certificate of Origin (DCO) compliance.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

Summary by CodeRabbit

• Bug Fixes
  • Improved multipart upload reliability by centralizing per-part retry behavior and standardizing returned completion data.
  • Ensured that failures in one part during concurrent multipart uploads don’t contaminate results from other parts.
• Tests
  • Added unit tests covering successful part uploads, correct error propagation with no partial results on failure, and concurrent multipart scenarios to verify error isolation per part.

[coderabbitai]

📝 Walkthrough

Walkthrough

Multipart part uploads now use a dedicated retrying helper that returns completed-part metadata. Concurrent upload handling delegates to this helper, and tests cover successful uploads, propagated failures, and per-part error isolation.

Changes

Multipart upload isolation

Layer / File(s)	Summary
Part upload helper and concurrency tests src/compute-plane-services/worker-utils/worker/large.go, src/compute-plane-services/worker-utils/worker/large_helpers_test.go	Adds an S3 part uploader abstraction and retrying uploadPart helper, with tests for success, failure propagation, and concurrent per-part error isolation.
Multipart upload integration src/compute-plane-services/worker-utils/worker/large.go	Updates concurrent multipart uploads to call uploadPart and append returned completed parts under the existing mutex.

Estimated code review effort: 3 (Moderate) | ~20 minutes

Suggested reviewers: vrv3814

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title uses a valid Conventional Commits fix(scope) format and accurately describes the multipart upload race fix.
Linked Issues check	✅ Passed	The changes address issue #442 by moving per-part upload error/result state into goroutine-local logic and adding targeted tests.
Out of Scope Changes check	✅ Passed	All changes stay focused on multipart upload race handling and test coverage, with no unrelated scope introduced.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

Warning

There were issues while running some tools. Please review the errors and either fix the tool's configuration or disable the tool if it's a critical failure.

🔧 golangci-lint (2.12.2)

level=error msg="[linters_context] typechecking error: pattern ./...: directory prefix . does not contain main module or its selected dependencies"

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[coderabbitai]

🧹 Nitpick comments (1)

src/compute-plane-services/worker-utils/worker/large.go (1)

251-253: 📐 Maintainability & Code Quality | 🔵 Trivial | ⚡ Quick win

Preserve the failing part number in the returned error.

This new error boundary returns the raw SDK error, so errgroup.Wait() cannot identify which part failed. Wrap it with %w and include partInput.PartNumber while preserving errors.Is behavior.

As per path instructions, Go changes under src/** should follow subtree error-handling conventions and preserve error context with %w.

Proposed fix

-		return types.CompletedPart{}, err
+		return types.CompletedPart{}, fmt.Errorf("upload part %d: %w", aws.ToInt32(partInput.PartNumber), err)

🤖 Prompt for AI Agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

In `@src/compute-plane-services/worker-utils/worker/large.go` around lines 251 -
253, Update the error return in the part-processing flow to wrap the SDK error
with `%w` and include `partInput.PartNumber` in the message, preserving
`errors.Is` compatibility while allowing `errgroup.Wait()` callers to identify
the failed part.

Source: Path instructions

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Nitpick comments:
In `@src/compute-plane-services/worker-utils/worker/large.go`:
- Around line 251-253: Update the error return in the part-processing flow to
wrap the SDK error with `%w` and include `partInput.PartNumber` in the message,
preserving `errors.Is` compatibility while allowing `errgroup.Wait()` callers to
identify the failed part.

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ℹ️ Review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Enterprise

Run ID: b35d84c1-0bf7-4299-ad81-a64761204e3d

📥 Commits

Reviewing files that changed from the base of the PR and between c2d83bc and 126504f.

📒 Files selected for processing (2)

• src/compute-plane-services/worker-utils/worker/large.go
• src/compute-plane-services/worker-utils/worker/large_helpers_test.go

🚧 Files skipped from review as they are similar to previous changes (1)

• src/compute-plane-services/worker-utils/worker/large_helpers_test.go