crates/evaluator: eval loop with git polling and nix-eval-jobs integration

Signed-off-by: NotAShelf <raf@notashelf.dev>
Change-Id: I291a411b1b06cf821e09f3d5a61403196a6a6964

crates/evaluator/src/git.rs

@@ -0,0 +1,28 @@
+use std::path::{Path, PathBuf};
+
+use fc_common::error::Result;
+use git2::Repository;
+
+/// Clone or fetch a repository. Returns (repo_path, head_commit_hash).
+pub fn clone_or_fetch(url: &str, work_dir: &Path, project_name: &str) -> Result<(PathBuf, String)> {
+    let repo_path = work_dir.join(project_name);
+
+    let repo = if repo_path.exists() {
+        let repo = Repository::open(&repo_path)?;
+        // Fetch origin — scope the borrow so `remote` is dropped before we move `repo`
+        {
+            let mut remote = repo.find_remote("origin")?;
+            remote.fetch(&["refs/heads/*:refs/remotes/origin/*"], None, None)?;
+        }
+        repo
+    } else {
+        Repository::clone(url, &repo_path)?
+    };
+
+    // Get HEAD commit hash
+    let head = repo.head()?;
+    let commit = head.peel_to_commit()?;
+    let hash = commit.id().to_string();
+
+    Ok((repo_path, hash))
+}