I think the most important thing is not whether your patent will be leaked by the agent, but whether you can fully express what you want to express when writing. Incomplete statement, patents could not be authorized at that time, because many patents could not be authorized and spent money in vain. In that case, you have leaked the technology and finally got the patent.
The premise of cooperation must be that you apply for an invention, and then big companies will be willing to cooperate with you, otherwise you will have no guarantee. If you apply for a patent, if it shows great value, more than one company may come to you.
You can visit an agency on the spot and then repeatedly confirm the contents of the patent written by it. This kind of patent authorization is promising.