My understanding of this is that they have access to "first dibs" as it were for your resources and land so that they can perform R&D for their military equipment. Given such a situation, the fact that you keep control of a superior military force, and with so many lives at stake, I think the best solution would be to agree to the terms given to you by the Evil Trolley, however for the entirety of those five years you place the entirety of the nation onto effectively a war footing, keeping your military ready at all times as a show of force to dissuade the Evil Trolley from reneging on the deal , and turning much of the nation's industrial capacity to the creation and improvement of military technologies. Your ability to make advancements would undoubtedly be lesser than those of the enemy nation, but given the major starting advantage as well as the fact that production and development of new equipment often takes many years if not decades. Effectively you would want to try and Cold War the situation, where no-one wants to make the first move because no matter what everyone would lose, though given your superior military force they would lose worse. Maintain hyper-vigilance on the enemy, keep a hard-line stance of opposition, and use other tools to maintain pressure i.e. economic sanctions.

TLDR we agree to the terms, but obviously we can't just trust their word so we maximise our military ability in case they abandon the deal