Function commit_present_on_remote 

pub fn commit_present_on_remote(
    workspace_root: &Path,
    commit_sha: &str,
) -> Result<bool, GitError>

True iff commit_sha appears on at least one origin/* remote- tracking branch (the SDK’s push-first precheck).

Does NOT run git fetch first — we want the precheck to be honest about the user’s local state. The SDK surfaces a “push your branch first” message that’s actionable, not a “ran fetch and still couldn’t find it” indirection. Users who routinely fetch via git pull --rebase etc. will never hit this; users who didn’t will see the precheck reject and run git push.