Deploying Bedrock/Sage9 with Capistrano. How to run composer in both folders?

So I’ve managed to use Capistrano to deploy Bedrock (Trellis isn’t an option for us) and have run into an issue.

You must also run composer install in the themes directory, and not just the root directory, when deploying.

I’ve tried all sorts of things, the closest I got is for some reason running the composer install in the previous releases directory.

set :theme_path, "#{release_path}/web/app/themes/coinninja"

desc "Build"
after :updated, :build do
	on roles(:app) do
		within release_path do
			execute :composer, "install --no-dev --quiet"
			execute "cd #{fetch(:theme_path)}; composer install --no-dev --quiet"

For some reason {release_path} gives me /current/ and not the new releases directory. So it ends up installing composer for the theme in the previous release only.