At the moment rattler-build downloads all the packages to the cache to get to the run exports. This works fine if the package will also be used during installations but is quite slow if we only care about the rendered recipe.

With prefix-dev/rattler-build#1114 merged, there is an object that is responsible for this behavior. The object should have an alternative code path to get the run-exports by different means if the fully extracted packages are not required at all.

We could implement a different mechanic by reading the package in memory and only extracting the parts we care about. We could also look into range requests similar to what we do in our backend.

This is a separate issue from providing run_exports in the repodata. Extracting the data from the package is only done if the repodata.json does not already contain run export information. Rattler-build already contains the behavior. Ideally we add run_exports to the repodata.json.