The two had just agreed upon is nothing more than a general direction for cooperation and the most significant deals involving their interests.
When the true expansion begins, the trade points between them are sure to be much more numerous than these.
For example, the giant livestock produced in the Giant Plains are not found in Ruitawen City. Once they've witnessed their hauling power, they will surely be tempted.
For example, the equipment worn by the Ruitawen Light Cavalry is something Gaven is particularly covetous of. If the Hobgoblin Wolf Cavalry could also be outfitted with such gear, they would be ready for mixed use as a versatile military force.
It's not about directly stripping the gear from the Ruitawen Light Cavalry, but rather about commissioning Ruitawen City to tailor-make their own sets.
The likelihood of mass equipping through external purchases is low; it's more probable that Ruitawen City has its own production line.