What is the meaning and force of “covenant” (Gen 9:9)?

It is not merely an agreement, because God’s covenants do not necessarily require anything of man, as here. It is also unlike an agreement in that there is no negotiation between the parties. That is, God hands each covenant down to man as a fait accompli; God’s covenants are all announced unilaterally by him. Usually man is required to do something, and there is punishment or loss of rights if he does not do that; but here, man has no requirements and it is just God declaring his intentions. A covenant also establishes, so to speak, the context in which God and man are thereafter to interact. It may include commands, laws, rewards, punishments, blessings, and curses—these all or mostly couched in the form of promises. You might call covenants “God’s parameters for man.”