How to fetch blobs from remote or alternate repositories

[kammerjaeger]

For CI processes we have repositories that are cloned with "--filter=blob:none".
Also we have a repository cache folder that we set via ".git/objects/info/alternates".

When we try to access the blob contend it fails, is there a way to download the blob from the remote repository?
For alternates objects I can probably just copy the objects over manually but I would prefer proper lib support.

What I'm looking for is something like https://git-scm.com/docs/partial-clone/2.49.0#_fetching_missing_objects
Manly ideas how to custom implement this or an integrated solution when using the lib.

Reproduction steps

Example repo setup:

git init $GITHUB_WORKSPACE/git --bare
git remote add origin git@github.com:${{ github.repository }}.git
echo "/git-cache/${{ github.repository }}.git/objects" >> ./objects/info/alternates
git fetch --no-tags --no-recurse-submodules --filter=blob:none origin ${{ env.DefaultBranch }}

Actual behavior

Depending on function: No valid git object identified by 'sha xxxxxx' exists in the repository.

Version of LibGit2Sharp (release number or SHA1)

0.31.0

Operating system(s) tested; .NET runtime tested

Win 11 / Debian | Net Core 8