test(template): M2.8 review nits — stale-binding comment + stale-ID & inert-check tests (#23)

Add code comments in ValidateConnectionBindingCompleteness explaining
that the unbound-attribute branch also covers the silently-dropped
stale-binding case (cross-reference FlatteningService.ApplyConnectionBindings),
and that the `continue` skips the exists-at-site check for unbound attrs.

Add two new tests:
- FlatteningPipelineConnectionBindingTests: stale DataConnectionId (999)
  not present in site connections → flattener drops it silently →
  validator reports ConnectionBinding Error, IsValid false.
- ValidationServiceTests: enforce:true + siteConnectionNames:null on a
  properly-bound attribute → no ConnectionBinding error (exists-at-site
  check stays inert when site set is not supplied).

tests/ZB.MOM.WW.ScadaBridge.DeploymentManager.Tests/FlatteningPipelineConnectionBindingTests.cs

@@ -96,4 +96,27 @@ public class FlatteningPipelineConnectionBindingTests
         Assert.DoesNotContain(result.Value.Validation.Errors,
             e => e.Category == ValidationCategory.ConnectionBinding);
     }
+
+    [Fact]
+    public async Task FlattenAndValidate_BindingToStaleDeletedConnection_ReportsBindingError()
+    {
+        // M2.8 (#23): FlatteningService.ApplyConnectionBindings silently drops a
+        // binding whose DataConnectionId doesn't resolve to any loaded site
+        // DataConnection (stale / deleted connection). The flattener leaves
+        // BoundDataConnectionId == null, so the validator treats the attribute as
+        // unbound and gates the deployment with a ConnectionBinding Error.
+        //
+        // Arrange: the instance binding points at id 999, but the site only has
+        // the connection with id=ConnectionId (7). The flattener can't resolve 999
+        // and drops the binding silently; the validator then flags it.
+        const int StaleConnectionId = 999;
+        Arrange(boundConnectionId: StaleConnectionId);
+
+        var result = await _sut.FlattenAndValidateAsync(InstanceId);
+
+        Assert.True(result.IsSuccess);
+        Assert.False(result.Value.Validation.IsValid);
+        Assert.Contains(result.Value.Validation.Errors,
+            e => e.Category == ValidationCategory.ConnectionBinding);
+    }
 }

tests/ZB.MOM.WW.ScadaBridge.TemplateEngine.Tests/Validation/ValidationServiceTests.cs

@@ -298,6 +298,36 @@ public class ValidationServiceTests
         Assert.False(result.IsValid);
     }
 
+    [Fact]
+    public void Validate_BoundAttributeWithNoSiteSet_DeployTime_ExistsAtSiteCheckIsInert()
+    {
+        // M2.8 (#23): when siteConnectionNames is null the "exists at site" half of the
+        // binding check stays inert — a properly-bound data-sourced attribute must NOT
+        // produce a ConnectionBinding error, even under deploy-time enforcement.
+        // This pins the contract: passing enforce:true + siteConnectionNames:null is safe
+        // (e.g. when the caller doesn't have a site connection set available yet).
+        var config = new FlattenedConfiguration
+        {
+            InstanceUniqueName = "Instance1",
+            Attributes =
+            [
+                new ResolvedAttribute
+                {
+                    CanonicalName = "Temp",
+                    DataType = "Double",
+                    DataSourceReference = "ns=2;s=Temp",
+                    BoundDataConnectionId = 7,
+                    BoundDataConnectionName = "PlantBus"
+                }
+            ]
+        };
+
+        var result = _sut.Validate(config, enforceConnectionBindings: true, siteConnectionNames: null);
+
+        Assert.DoesNotContain(result.Errors, e => e.Category == ValidationCategory.ConnectionBinding);
+        Assert.True(result.IsValid);
+    }
+
     [Fact]
     public void Validate_EmptyConfig_ReturnsWarning()
     {