🗄️ Lưu ký & Back-office

A share is not a piece of paper any more — it is a row in a ledger, and the question of which ledger is the real one runs through everything here. Notes from the builder's side: why a client holding 1,000 shares may only be able to sell 600, why one quantity column can never answer that, the invariant that your clients' balances must equal your account at the depository for every single symbol, and why a mismatch means stop rather than guess.