fix(transport): skip unbound (empty ConnectionName) bindings on import instead of writing FK=0 (M8 INT review)

src/ZB.MOM.WW.ScadaBridge.Transport/Import/BundleImporter.cs

@@ -3237,25 +3237,28 @@ public sealed class BundleImporter : IBundleImporter
         }
         foreach (var b in dto.ConnectionBindings)
         {
+            // A binding may carry NO connection name — an unbound attribute, or a
+            // binding whose source connection was not included in the export. There
+            // is no meaningful target FK to write (DataConnectionId = 0 would be an
+            // invalid FK and FK-violate at commit on a relational provider), so skip
+            // the binding row entirely rather than persist a broken binding.
+            if (string.IsNullOrEmpty(b.ConnectionName))
+            {
+                continue;
+            }
             // Resolve ConnectionName → target DataConnectionId. After the C1 Pass-2
             // in ApplyDataConnectionsAsync, the map carries an entry for every
             // referenced connection — carried in the bundle OR auto-matched in the
-            // target. A binding whose connection name STILL doesn't resolve is a
-            // structural error (it should already have been a preview blocker +
-            // a pre-write validation failure); THROW rather than write
-            // DataConnectionId = 0, which would be an invalid FK on a relational
-            // provider and a silently-broken binding on the in-memory one.
-            // A binding may legitimately carry NO connection name (unbound
-            // attribute) — only a NON-EMPTY name that fails to resolve is an error.
-            if (!string.IsNullOrEmpty(b.ConnectionName)
-                && !connectionMaps.IdBySourceRef.TryGetValue((sourceSiteIdentifier, b.ConnectionName), out _))
+            // target. A non-empty name that STILL doesn't resolve is a structural
+            // error (it should already have been a preview blocker + a pre-write
+            // validation failure); THROW rather than write an invalid FK.
+            if (!connectionMaps.IdBySourceRef.TryGetValue((sourceSiteIdentifier, b.ConnectionName), out var connId))
             {
                 throw new InvalidOperationException(
                     $"Instance '{inst.UniqueName}' binding for attribute '{b.AttributeName}' references "
                     + $"connection '{sourceSiteIdentifier}/{b.ConnectionName}' which could not be resolved "
                     + "to a target connection (present in neither bundle nor target).");
             }
-            connectionMaps.IdBySourceRef.TryGetValue((sourceSiteIdentifier, b.ConnectionName), out var connId);
             inst.ConnectionBindings.Add(new InstanceConnectionBinding(b.AttributeName)
             {
                 DataConnectionId = connId,