I was looking for a way to force node-gyp to re-download the headers even if the directory already exists in $npm_config_devdir/$node_version, and I found --ensure, which seems to do the opposite.

As I understand it, node-gyp doesn't download the headers unless the directory is missing, so --ensure is the default behaviour. Am I missing something? Is there a --always-redownload option (and should there be)?

Obviously as a workaround you can do this before the node-gyp rebuild or npm install:

node "$(npm config get prefix)"/lib/node_modules/npm/node_modules/node-gyp/bin/node-gyp.js remove $(node -p process.versions.node)