That is fine, but it is you that has the contract with Agent A and it will be you that is sued if some that didn't make an offer but was introduced by Agent A buys the property from you with agent B.
For privacy reasons I can't see A handing over a list to B either - also for marketing...
I would think anyone that was showed the property by the first agent would be 'introduced' by that agent.
You should get a special condition inserted into the contract that buyers were introduced by the 2nd agent and the buyer will be liable to the first agent if there is any extra commission...
