fix: don't clobber unset interface fields on partial update

update_interface dumped the full InterfaceUpdate model without
exclude_unset, so any partial update (e.g. description only) sent None
for every other field including port, tripping interface.port's NOT
NULL constraint and 500ing. Now the DB write only applies fields the
caller actually sent; configure_interface still gets the full merged
state since it indexes port/mode/etc unconditionally.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

Author: thangphan205

backend/app/crud/interfaces.py

@@ -108,19 +108,22 @@ def update_interface(
     """
     Update an interface.
     """
-    # update local database
-    update_dict = interface_in.model_dump()
+    # update local database — only touch fields the caller actually sent,
+    # so omitted fields (e.g. port) don't get clobbered with None
+    update_dict = interface_in.model_dump(exclude_unset=True)
     update_dict["updated_at"] = datetime.now()
     interface_db.sqlmodel_update(update_dict)
     session.add(interface_db)
     session.commit()
     session.refresh(interface_db)
-    # update running config
+    # update running config — configure_interface needs the full merged
+    # state (existing values + whatever changed), not just what was sent
+    full_dict = interface_db.model_dump()
     if update_running_config:
-        configure_interface(switch=switch, interface_info=update_dict)
+        configure_interface(switch=switch, interface_info=full_dict)
         # Reflect configured VLAN list back into DB so Current State stays accurate
-        if update_dict.get("mode") == "trunk" and update_dict.get("allowed_vlan_add"):
-            interface_db.allowed_vlan = update_dict["allowed_vlan_add"]
+        if full_dict.get("mode") == "trunk" and full_dict.get("allowed_vlan_add"):
+            interface_db.allowed_vlan = full_dict["allowed_vlan_add"]
             session.add(interface_db)
             session.commit()
             session.refresh(interface_db)