One of the projects I'm working on has a CI/CD pipeline that builds Docker images. The Dockerfile runs yarn install, then yarn build. The latter runs the TypeScript compiler tsc. Everything was working fine, but one day the build failed with the following error:

tsc: command not found

But TypeScript is still part of package.json. Nobody touched package.json or yarn.lock recently. Nobody could reproduce the problem locally with Docker: it only happened in the CI/CD pipeline. What is going on? We needed to debug the Docker build on the CI/CD server.

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