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My tests with @yarnpkg instead of #npm were fine, until I found out, #yarn always validates devDependencies: github.com/yarnpkg/yarn/issues/3630 That ends in an error in my deployment container, because I have one devDependency, requiring a special node version.
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Switched back to #npm and deployment runs like a charm. Without trying to do anything with the devDependencies. Just like it should.