Preserve exchange allocations during atomic replacement and reserve generated aliases

crates/oa-core/src/references.rs

@@ -203,6 +203,9 @@ pub fn remap_references(p: &mut Project, old: Id, new: Id) {
 }
 /// IDs removed by a cascade. Cross-layer traced counterparts are never included.
 pub fn deletion_impact(p: &Project, id: Id) -> BTreeSet<Id> {
+    deletion_impact_inner(p, id, false)
+}
+fn deletion_impact_inner(p: &Project, id: Id, defer_exchange_allocations: bool) -> BTreeSet<Id> {
     let mut removed = BTreeSet::from([id]);
     loop {
         let before = removed.len();
@@ -254,12 +257,15 @@ pub fn deletion_impact(p: &Project, id: Id) -> BTreeSet<Id> {
             else {
                 continue;
             };
-            if p.relations.values().any(|allocation| {
-                allocation.kind() == RelationKind::PortAllocation
-                    && removed.contains(&allocation.id)
-                    && [boundary.source(), boundary.target()].contains(&allocation.source())
-                    && [*source_port, *target_port].contains(&allocation.target())
-            }) {
+            if !defer_exchange_allocations
+                && p.relations.values().any(|allocation| {
+                    allocation.kind() == RelationKind::PortAllocation
+                        && removed.contains(&allocation.id)
+                        && [boundary.source(), boundary.target()].contains(&allocation.source())
+                        && [*source_port, *target_port].contains(&allocation.target())
+                })
+                && crate::ports::missing_exchange_port_allocations(p, r, &removed)
+            {
                 removed.insert(r.id);
             }
         }
@@ -288,6 +294,40 @@ pub fn deletion_impact(p: &Project, id: Id) -> BTreeSet<Id> {
 }
 pub fn delete_cascade(p: &mut Project, id: Id) {
     let removed = deletion_impact(p, id);
+    remove_objects(p, removed);
+}
+/// Preserve conditional exchange-allocation dependents until the transaction
+/// has had the opportunity to supply explicit replacement allocation facts.
+pub(crate) fn delete_cascade_deferred(p: &mut Project, id: Id, pending: &mut BTreeSet<Id>) {
+    let complete = deletion_impact(p, id);
+    let removed = deletion_impact_inner(p, id, true);
+    // An explicitly removed relation cannot pass its conditional cascade on
+    // to a new relation that later reuses the same identity in this batch.
+    pending.retain(|id| !removed.contains(id));
+    pending.extend(
+        complete
+            .difference(&removed)
+            .filter(|id| {
+                p.relations
+                    .get(id)
+                    .is_some_and(|r| r.kind() == RelationKind::ExchangeAllocation)
+            })
+            .copied(),
+    );
+    remove_objects(p, removed);
+}
+pub(crate) fn finish_deletions(p: &mut Project, pending: &BTreeSet<Id>) {
+    let none = BTreeSet::new();
+    for id in pending {
+        if p.relations.get(id).is_some_and(|r| {
+            r.kind() == RelationKind::ExchangeAllocation
+                && crate::ports::missing_exchange_port_allocations(p, r, &none)
+        }) {
+            delete_cascade(p, *id);
+        }
+    }
+}
+fn remove_objects(p: &mut Project, removed: BTreeSet<Id>) {
     let removed_names: std::collections::BTreeMap<_, _> = removed
         .iter()
         .map(|id| (*id, p.named(*id).to_string()))