fix(client): surface nested error bodies and implement --debug

.changes/next-release/bugfix-client-4qrbt6n2.json

@@ -0,0 +1,5 @@
+{
+  "type": "bugfix",
+  "category": "client",
+  "description": "Surface nested API error bodies ({\"error\":{\"message\":...}}) instead of a bare HTTP status, and make the --debug flag log request/response"
+}

go/internal/client/client.go

@@ -8,6 +8,8 @@ import (
 	"io"
 	"net/http"
 	"net/url"
+	"os"
+	"strings"
 	"time"
 
 	"github.com/vngcloud/greennode-cli/internal/auth"
@@ -191,6 +193,14 @@ func (c *GreenodeClient) requestRaw(method, path string, params map[string]strin
 		req.Header.Set("Authorization", "Bearer "+token)
 		req.Header.Set("Content-Type", "application/json")
 
+		if c.debug {
+			fmt.Fprintf(os.Stderr, "[debug] %s %s\n", method, fullURL)
+			if body != nil {
+				jsonBody, _ := json.Marshal(body)
+				fmt.Fprintf(os.Stderr, "[debug] request body: %s\n", string(jsonBody))
+			}
+		}
+
 		resp, err := c.httpClient.Do(req)
 		if err != nil {
 			lastErr = err
@@ -205,6 +215,10 @@ func (c *GreenodeClient) requestRaw(method, path string, params map[string]strin
 		respBody, _ := io.ReadAll(resp.Body)
 		resp.Body.Close()
 
+		if c.debug {
+			fmt.Fprintf(os.Stderr, "[debug] response %d: %s\n", resp.StatusCode, string(respBody))
+		}
+
 		// 401 — refresh token and retry once
 		if resp.StatusCode == http.StatusUnauthorized {
 			token, err = c.tokenManager.RefreshToken()
@@ -266,6 +280,12 @@ func formatError(statusCode int, body []byte) string {
 				}
 			}
 		}
+		// Fallback: the error payload didn't use a known string field (e.g. the
+		// VKS API returns {"error": {...}} as a nested object). Surface the raw
+		// JSON body so the server's message isn't silently dropped.
+		if detail == "" && len(body) > 0 {
+			detail = strings.TrimSpace(string(body))
+		}
 	} else {
 		detail = string(body)
 	}

go/internal/client/client_test.go

@@ -4,6 +4,7 @@ import (
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
 	"time"
 
@@ -39,3 +40,21 @@ func TestPatchSendsPatchMethodAndBody(t *testing.T) {
 		t.Errorf("body = %q, want enableAutoHealing payload", gotBody)
 	}
 }
+
+func TestFormatErrorSurfacesNestedErrorObject(t *testing.T) {
+	// VKS returns errors as {"error": {"message": ...}} — a nested object, not a
+	// string. The detail must still reach the user instead of being dropped.
+	body := []byte(`{"error":{"message":"KubeConfig can only be requested when the cluster is ACTIVE."}}`)
+	got := formatError(http.StatusBadRequest, body)
+	if !strings.Contains(got, "cluster is ACTIVE") {
+		t.Errorf("formatError = %q, want it to contain the nested error message", got)
+	}
+}
+
+func TestFormatErrorUsesPlainStringMessage(t *testing.T) {
+	body := []byte(`{"message":"boom"}`)
+	got := formatError(http.StatusBadRequest, body)
+	if !strings.Contains(got, "boom") {
+		t.Errorf("formatError = %q, want it to contain %q", got, "boom")
+	}
+}