[xavier-greenline]

Requirements

• I have added test coverage for new or changed functionality
• I have followed the repository's pull request submission guidelines
• I have validated my changes against all supported platform versions (tested locally on macOS arm64, and the change uses no platform-specific code)

Related issues

Closes #860

Describe the solution you've provided

• Replaces the sequential PUT loop with errgroup, limited to 8 uploads at a time.
• Like the current loop, the command stops at the first failed upload and returns its error. Uploads already in progress finish first.
• golang.org/x/sync moves from an indirect to a direct dependency.
• One test asserts that more than one upload runs at once and never more than the limit. Setting the limit to 1 makes it fail, so it catches a return to sequential uploads.
• Another test asserts that a failure stops new uploads from starting.

Describe alternatives you've considered

Left for maintainers to decide:

• A --concurrency flag, where 1 restores sequential uploads. I left it out to keep the change small, though the timings in sourcemaps upload sends files one at a time #860 show the limit matters.
• The default of 8. A limit of 16 cuts the .next/server upload from about 60 s to 37 s, but 8 is safer for shared CI runners and for presigned-URL rate limits we cannot see.
• Fail-fast versus uploading every file and reporting all failures.

Additional context

The [LaunchDarkly] Uploaded … lines now print in completion order rather than directory walk order.

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Note

Overview
sourcemaps upload now PUTs each file to its presigned URL in parallel (up to 8 at a time) via golang.org/x/sync/errgroup, replacing the previous one-by-one loop. A new uploadFiles helper owns that orchestration; the command still fails on the first upload error and does not start new work after a failure (in-flight uploads may finish).

Tests cover that concurrency stays above 1 and at or below the cap, and that a 403 stops before every file is attempted. golang.org/x/sync is a direct module dependency. Progress lines [LaunchDarkly] Uploaded … may appear in completion order instead of walk order.

^{Reviewed by Cursor Bugbot for commit e32b56b. Bugbot is set up for automated code reviews on this repo. Configure here.}

[ld-ahartmann]

neat! I agree the concurrency flag can be left out

[xavier-greenline]

Thanks @ld-ahartmann. I've merged the latest main into the branch. How do you want to proceed?

[nieblara]

hey @xavier-greenline ill take this one from here!