I'm not aware of such a guarantee. The Joint Declaration and Constitution are both somewhat ambiguous on that point and that's part of the problem, though the Basic Law is clearer in terms of specifics and it seems to rule out such an outcome in its present form.
Article 45 of the
Basic Law declares:
The Chief Executive of the Hong Kong Special Administrative Region shall be selected by election or through consultations held locally and be appointed by the Central People’s Government.
The method for selecting the Chief Executive shall be specified in the light of the actual situation in the Hong Kong Special Administrative Region and in accordance with the principle of gradual and orderly progress. The ultimate aim is the selection of the Chief Executive by universal suffrage upon nomination by a broadly representative nominating committee in accordance with democratic procedures.
The
Joint Declaration states:
The Government of the Hong Kong Special Administrative Region will be composed of local inhabitants. The chief executive will be appointed by the Central People's Government on the basis of the results of elections or consultations to be held locally.
The Hong Kong
Constitution states:
The government and legislature of the Hong Kong Special Administrative Region shall be composed of local inhabitants. The chief executive of the Hong Kong Special Administrative Region shall be selected by election or through consultations held locally and be appointed by the Central People's Government.
In the protesters' view, the Joint Declaration and Constitution, which omit references to a nominating Committee, allow for direct nominations. In part, the protesters believe that the Chinese government is in a position to influence the electoral process beyond the intent of the Joint Declaration through the nominating committee process, hence they want no part of such a committee role. Instead, they want direct democratic elections.
The Chinese government views the nominating committee as fully consistent with all of Hong Kong's laws. Given that the committee is dominated by pro-Beijing members, the Chinese government is unwilling to change a situation that gives it some degree of ability to shape Hong Kong's leadership outcome. The Chinese government is very reluctant to grant any greater degree of autonomy to Hong Kong than it currently possesses, hence it will likely maintain a firm position.
Whether or not there is a pragmatic middle course i.e., broader nominating committee membership, a meaningful share of the nominating committee's members ultimately being elected by Hong Kong's residents in the future, etc., to accommodate both parties remains to be seen.