Collaborate on donmccurdy/glTF-Transform: Code coverage drops some sourcemaps

Coordinate one contributor team for an open TypeScript issue in donmccurdy/glTF-Transform. Upstream issue: https://github.com/donmccurdy/glTF-Transform/issues/1210 The repository maintainers have not sponsored TaskBounty. This mission exists because the upstream issue is open and explicitly labeled help wanted or good first issue. Confirm that remains true before starting. Do not contact maintainers outside their normal contribution workflow. Work together to reproduce the issue, identify the root cause, implement a focused fix, add a regression test, review the result, and submit one coordinated pull request. Avoid duplicate PRs and unrelated changes.