feat: expose read-only local review CLI

src/repository.rs

@@ -1091,22 +1091,35 @@ pub struct Repository {
     comparison: Option<PreparedComparison>,
     cancelled: Arc<AtomicBool>,
 }
+/// Discover the canonical checkout root without opening a comparison repository.
+pub fn discover_root(path: &Path) -> Result<PathBuf, String> {
+    discover_root_with_cancellation(path, &AtomicBool::new(false))
+}
+
+fn discover_root_with_cancellation(path: &Path, cancelled: &AtomicBool) -> Result<PathBuf, String> {
+    let path = fs::canonicalize(path).map_err(|error| error.to_string())?;
+    let root = path
+        .ancestors()
+        .find(|path| path.join(".jj").exists() || path.join(".git").exists())
+        .ok_or("No Jujutsu or Git working-tree repository found")?;
+    if root.join(".jj").exists() {
+        let mut command = jj_command(root);
+        command.arg("root");
+        let output = checked(run(command, vec![], cancelled)?)?;
+        let root = path_bytes(output.strip_suffix(b"\n").unwrap_or(&output))?;
+        fs::canonicalize(root).map_err(|error| error.to_string())
+    } else {
+        Ok(root.to_path_buf())
+    }
+}
+
 impl Repository {
     pub fn open(root: &Path, cancelled: Arc<AtomicBool>) -> Result<Self, String> {
-        let root = fs::canonicalize(root).map_err(|e| e.to_string())?;
-        let discovered = root
-            .ancestors()
-            .find(|p| p.join(".jj").exists() || p.join(".git").exists())
-            .ok_or("No Jujutsu or Git working-tree repository found")?;
-        let (root, kind, store) = if discovered.join(".jj").exists() {
-            let mut cmd = jj_command(discovered);
-            cmd.arg("root");
-            let output = checked(run(cmd, vec![], &cancelled)?)?;
-            let actual = path_bytes(output.strip_suffix(b"\n").unwrap_or(&output))?;
+        let actual = discover_root_with_cancellation(root, &cancelled)?;
+        let (root, kind, store) = if actual.join(".jj").exists() {
             let store = store_for_jj(&actual)?;
             (actual, RepoKind::Jujutsu, store)
         } else {
-            let actual = discovered.to_path_buf();
             let mut cmd = Command::new("git");
             cmd.arg("-C")
                 .arg(&actual)