git: match native agent workflows

userland/git/src/changes.rs

@@ -373,6 +373,18 @@ pub fn diff(p: DiffParams) -> Result<Vec<FileDiff>> {
     let repo = repo::open(&p.repo)?;
     let (old, new, work) = match (&p.from, &p.to, p.staged.unwrap_or(false)) {
         (Some(a), Some(b), false) => (tree(&repo, a)?, tree(&repo, b)?, false),
+        (Some(a), None, staged) => {
+            let (index, _) = index(&repo)?;
+            if staged {
+                (tree(&repo, a)?, index, false)
+            } else {
+                (
+                    tree(&repo, a)?,
+                    worktree(&repo, &index, p.path.as_deref())?,
+                    true,
+                )
+            }
+        }
         (None, None, staged) => {
             repo::worktree(&repo)?;
             let (index, conflicts) = index(&repo)?;