As of today, the standard way to add a dependency to a Tuleap npm package is to use link: protocol. pnpm does it by default when you use pnpm add with a relative path. It works well. The only exception is that filtering with dependencies (pnpm --filter ...foo test) only selects the foo package in our case. For this to work, we should use the workspace protocol. After trying it out, it does not seem to break the turbo cache: the cache is hit or invalidated correctly.
Since it seems to be transparent enough, we should switch to workspace: protocol to enable filtering with dependencies.