To recreate:

1. add the nativescript-app-sync to the project (with tns plugin add nativescript-app-sync
2. start a cloud iOS build in Sidekick.
3. the build fails on npm install...

The error looks the same as described here ProgressNS/sidekick-feedback#288, nativescript-app-sync's postinstall hook is trying to install something into '/usr/local/lib/node_modules', which it is not allowed...

Detailed sidekick log available here https://gist.github.com/miiihi/3967f3ced0210a1d7297fbfebc7e4016