creating new wc commit when @ becomes immuable

cli/src/cli_util.rs

@@ -1313,6 +1313,17 @@ See https://github.com/martinvonz/jj/blob/main/docs/working-copy.md#stale-workin
                 // update it.
             }
         }
+
+        let current_wc = self.repo().view().wc_commit_ids().get(self.workspace_id());
+        if let Some(wc) = current_wc {
+            if self.check_rewritable([wc]).is_err() {
+                writeln!(
+                    ui.warning_default(),
+                    "@ became immutable. You should create a new commit using jj new."
+                )?;
+                // Here i should create a new commit.
+            }
+        }
         let settings = &self.settings;
         if settings.user_name().is_empty() || settings.user_email().is_empty() {
             writeln!(