refactor: Move ComputeVPNGateway to identity and refs pattern (#11590)

Please follow the skill .gemini/skills/kcc-identity-reference/SKILL.md
for ComputeVPNGateway.

Fixes #11588

Author: justinsb

.gemini/skills/kcc-identity-reference/journal/ComputeVPNGateway.md

@@ -0,0 +1,7 @@
+# ComputeVPNGateway Identity and Reference Journal
+
+## Observations & Learnings
+
+- **Regional Scope Integration:** `ComputeVPNGateway` is a regional resource in GCP, meaning its URL pattern contains `/regions/{region}/` and has a region parameter: `projects/{project}/regions/{region}/vpnGateways/{vpngateway}`.
+- **Implement ParentString:** We implemented the standard `ParentString()` method to return the parent regional path `projects/{project}/regions/{region}`, ensuring alignment with standard direct controller expectations and other regional compute resources.
+- **Fallback Normalize Integration:** In `computevpngateway_reference.go`, we updated the fallback mechanism inside `Normalize` to use the robust standard pattern leveraging `common.ToStructuredType` and `getIdentityFromComputeVPNGatewaySpec` when `status.selfLink` is not yet available, ensuring full compatibility and robust reference resolution.

apis/compute/v1beta1/computevpngateway_identity.go

@@ -63,6 +63,10 @@ func (i *ComputeVPNGatewayIdentity) Host() string {
 	return ComputeVPNGatewayIdentityFormat.Host()
 }
 
+func (i *ComputeVPNGatewayIdentity) ParentString() string {
+	return fmt.Sprintf("projects/%s/regions/%s", i.Project, i.Region)
+}
+
 func ParseComputeVPNGatewayExternal(external string) (*ComputeVPNGatewayIdentity, error) {
 	if external == "" {
 		return nil, fmt.Errorf("empty ComputeVPNGateway external value")

apis/compute/v1beta1/computevpngateway_identity_test.go

@@ -68,3 +68,15 @@ func TestComputeVPNGatewayIdentity_FromExternal(t *testing.T) {
 		})
 	}
 }
+
+func TestComputeVPNGatewayIdentity_ParentString(t *testing.T) {
+	id := &ComputeVPNGatewayIdentity{
+		Project:    "my-project",
+		Region:     "us-central1",
+		VpnGateway: "my-vpn-gateway",
+	}
+	expected := "projects/my-project/regions/us-central1"
+	if actual := id.ParentString(); actual != expected {
+		t.Fatalf("expected %q, got %q", expected, actual)
+	}
+}

apis/compute/v1beta1/computevpngateway_reference.go

@@ -93,7 +93,11 @@ func (r *ComputeVPNGatewayRef) Normalize(ctx context.Context, reader client.Read
 		// Get external from status.selfLink. This ensures backward compatibility for TF/DCL-based resources that lack status.externalRef.
 		selfLink, _, _ := unstructured.NestedString(u.Object, "status", "selfLink")
 		if selfLink != "" {
-			return apirefs.TrimComputeURIPrefix(selfLink)
+			trimmed := apirefs.TrimComputeURIPrefix(selfLink)
+			id := &ComputeVPNGatewayIdentity{}
+			if err := id.FromExternal(trimmed); err == nil {
+				return id.String()
+			}
 		}
 		return ""
 	}