feat: show jj ancestry in the floating diff picker

tests/repository.rs

@@ -1367,6 +1367,31 @@ fn jj_private_fetch_discovers_never_fetched_bookmark_and_searchable_remote_chang
     );
     assert_eq!(changed(&comparison, Path::new("file")).after, ["local"]);
     let loaded = repository.fetch_remote("origin").unwrap();
+    assert_eq!(loaded.graph[&tip].parents, [ancestor.clone()]);
+    assert_eq!(
+        loaded.graph[&ancestor].description,
+        "remote historic needle"
+    );
+    assert!(!loaded.graph[&tip].current);
+    let positions: std::collections::BTreeMap<_, _> = loaded
+        .entries
+        .iter()
+        .filter(|entry| entry.category == Category::Revisions)
+        .enumerate()
+        .filter_map(|(index, entry)| match &entry.target {
+            RevisionTarget::Commit(id) => Some((id.as_str(), index)),
+            _ => None,
+        })
+        .collect();
+    for (id, metadata) in &loaded.graph {
+        for parent in &metadata.parents {
+            if let (Some(child), Some(parent)) =
+                (positions.get(id.as_str()), positions.get(parent.as_str()))
+            {
+                assert!(child < parent);
+            }
+        }
+    }
     let historic = loaded
         .entries
         .iter()