I don't know based on the rulebook. The provided context does not specify whether players must discard their hand at the end of a round or if there is a hand size limit. The rules on page 13 describe how to draw, play, and discard cards during a turn, but do not mention any restrictions or requirements regarding hand size or retaining cards between rounds. Additional information from the rulebook would be needed to answer this question definitively.

Source: Core Rulebook (pp. 13, 18, 28, 7)