fix: API error message — parse JSON error body, show actual API message instead of raw status

internal/provider/rainyun/client.go

@@ -82,20 +82,9 @@ func (c *client) do(ctx context.Context, method, path string, body, result any)
 		return fmt.Errorf("read response: %w", err)
 	}
 
-	if resp.StatusCode >= 400 {
-		return &APIError{
-			StatusCode: resp.StatusCode,
-			Method:     method,
-			URL:        url,
-			Body:       respBody,
-		}
-	}
-
 	var apiResp apiResponse
-	if err := json.Unmarshal(respBody, &apiResp); err != nil {
+	if err := json.Unmarshal(respBody, &apiResp); err == nil {
-		return fmt.Errorf("unmarshal response: %w", err)
+		if resp.StatusCode >= 400 || apiResp.Code != 0 {
-	}
-	if apiResp.Code != 0 {
 			return &APIError{
 				StatusCode: resp.StatusCode,
 				Method:     method,
@@ -105,6 +94,14 @@ func (c *client) do(ctx context.Context, method, path string, body, result any)
 				APIMsg:     apiResp.Msg,
 			}
 		}
+	} else if resp.StatusCode >= 400 {
+		return &APIError{
+			StatusCode: resp.StatusCode,
+			Method:     method,
+			URL:        url,
+			Body:       respBody,
+		}
+	}
 
 	if result != nil {
 		if err := json.Unmarshal(respBody, result); err != nil {
@@ -126,7 +123,20 @@ type APIError struct {
 func (e *APIError) Error() string {
 	msg := e.APIMsg
 	if msg == "" {
+		// 非 JSON 响应，截取 body 前 200 字符
+		body := string(e.Body)
+		if len(body) > 200 {
+			body = body[:200] + "..."
+		}
+		if body != "" {
+			msg = body
+		} else {
 			msg = http.StatusText(e.StatusCode)
 		}
+	}
 	return msg
 }
+
+func (e *APIError) Detail() string {
+	return fmt.Sprintf("%s %s [%d]", e.Method, e.URL, e.StatusCode)
+}