fix(provider): always write known api_version after apply (#2)

api_version is Optional+Computed. For every non-Azure provider (Vertex
Gemini/Anthropic) it is unset in config, so its planned value is unknown.
apply() only assigned it when the gateway echoed a non-empty value, leaving
the attribute unknown after apply for Vertex providers and triggering
"Provider returned invalid result object after apply ... still indicated an
unknown value for ...api_version". This broke the 4 Vertex aigateway_provider
resources on the innfactory26 rollout (and, by cascade, the dependent azure
models received an empty provider_id).

Resolve to types.StringNull() when the gateway returns no api_version; Azure
still round-trips its echoed value. Adds unit tests covering both paths.

Author: jona7o

internal/provider/provider_resource.go

@@ -251,7 +251,13 @@ func (r *providerResource) apply(m *providerResourceModel, a *providerAPI) {
 	if a.ProjectID != "" {
 		m.ProjectID = types.StringValue(a.ProjectID)
 	}
+	// api_version is Optional+Computed: when unset in config (every non-Azure
+	// provider) its planned value is unknown, so we MUST write a known value
+	// here or Terraform rejects the result ("unknown value ... after apply").
+	// Azure sets it and the gateway echoes it; everyone else gets null.
 	if a.APIVersion != "" {
 		m.APIVersion = types.StringValue(a.APIVersion)
+	} else {
+		m.APIVersion = types.StringNull()
 	}
 }

internal/provider/provider_resource_test.go

@@ -0,0 +1,61 @@
+package provider
+
+import (
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-framework/types"
+)
+
+// api_version is Optional+Computed: when it is unset in config (every non-Azure
+// provider, e.g. Vertex) its planned value is UNKNOWN. apply() MUST resolve it
+// to a known value, otherwise Terraform rejects the result with
+// "Provider returned invalid result object after apply ... still indicated an
+// unknown value for ...api_version". This is the bug that broke the 4 Vertex
+// providers on the innfactory26 rollout.
+func TestProviderApplyResolvesUnknownAPIVersion(t *testing.T) {
+	r := &providerResource{}
+	m := &providerResourceModel{
+		APIVersion: types.StringUnknown(), // Vertex: unset in config => unknown plan value
+		Region:     types.StringValue("eu"),
+		ProjectID:  types.StringValue("proj-123"),
+	}
+	// The gateway omits apiVersion for non-Azure providers, so the decoded
+	// response carries the empty string.
+	a := &providerAPI{
+		ID:         "provider_abc",
+		Type:       "gemini",
+		Name:       "Vertex AI Gemini",
+		Endpoint:   "https://aiplatform.eu.rep.googleapis.com",
+		AuthType:   "serviceAccount",
+		Region:     "eu",
+		ProjectID:  "proj-123",
+		APIVersion: "",
+		Enabled:    true,
+	}
+
+	r.apply(m, a)
+
+	if m.APIVersion.IsUnknown() {
+		t.Fatal("api_version is Computed and must be KNOWN after apply, got unknown")
+	}
+	if !m.APIVersion.IsNull() {
+		t.Errorf("api_version should be null when the gateway returns none, got %q", m.APIVersion.ValueString())
+	}
+	if m.ID.ValueString() != "provider_abc" {
+		t.Errorf("id mismatch: got %q", m.ID.ValueString())
+	}
+}
+
+// Azure sets api_version in config; the gateway echoes it back. apply() must
+// preserve the value exactly (Optional+Computed round-trip).
+func TestProviderApplyPreservesAzureAPIVersion(t *testing.T) {
+	r := &providerResource{}
+	m := &providerResourceModel{APIVersion: types.StringValue("2024-10-21")}
+	a := &providerAPI{ID: "provider_x", APIVersion: "2024-10-21", Enabled: true}
+
+	r.apply(m, a)
+
+	if m.APIVersion.ValueString() != "2024-10-21" {
+		t.Errorf("azure api_version must round-trip, got %q", m.APIVersion.ValueString())
+	}
+}