feat: preserve nested source projects across desktop and REST

crates/oa-core/src/transitions.rs

@@ -1021,6 +1021,15 @@ pub fn plan_transition(
     Ok(plan)
 }
 pub fn apply_transition(project: &Project, plan: &TransitionPlan) -> Result<Project, ModelError> {
+    prepare_transition(project, plan).map(|prepared| prepared.project)
+}
+
+/// Prepare a reviewed transition once, retaining identity correspondence for
+/// adapters that update accepted graphical and authored source state together.
+pub fn prepare_transition(
+    project: &Project,
+    plan: &TransitionPlan,
+) -> Result<PreparedCommand, ModelError> {
     if project_fingerprint(project) != plan.base_fingerprint {
         return Err(ModelError(
             "Transition preview is stale; create a new preview.".into(),
@@ -1031,7 +1040,7 @@ pub fn apply_transition(project: &Project, plan: &TransitionPlan) -> Result<Proj
             "Resolve transition conflicts before applying.".into(),
         ));
     }
-    execute_batch(project, &plan.commands)
+    prepare_command(project, &Command::Batch(plan.commands.clone()))
 }
 
 /// Supported explicit element counterparts, in stable kind-catalog order.