C. F. Keil and Franz Delitzsch on Joshua 9:21

Jos 9:21

The princes declared again most emphatically, “They shall live.” Thus the Gibeonites became hewers of wood and drawers of water to the congregation, as the princes had said to them, i.e., had resolved concerning them. This resolution they communicated to the congregation at the time, using the expression יחיוּ (let them live); but the historian has passed this over at Jos 9:21, and instead of mentioning the resolution proceeds at once to describe its execution.