First: I'm probably in his address book, so my messages won't go to Junk.

You being in his contacts doesn't mean that your email won't end up in his junk folder. Contacts aren't automatically considered "safe senders".

He had no trouble receiving my emails a few months ago, when I had a problem at the client and asked for his help.

As is the nature of email and spam filtering. Things change every day. Spammers change their tactics and methods and spam filters change to stay at pace with those tactics and methods. What went to the Inbox today may very well end up in the Junk folder tomorrow.

I think it's known that this client does not like to give out raises, and so I suspect that he saw my email asking to negotiate for a raise, worried that it would derail an otherwise guaranteed renewal, and decided to duck my messages until all the paperwork was filed, hoping to make it a fait accompli. It's also a little suspicious that I got no response from any of my other contacts at the agency -- this makes me think they're closing ranks to help this shady gambit succeed.

If your email wound up in his junk folder then it's almost guaranteed that it wound up in the junk folder of everyone else at the agency. I don't find that particularly unusual or suspect.

It seems to me like I am at liberty to reject the agreement entirely, because it was made without my authorization or even my knowledge, and that it's up to me whether to give the recruiter any option to make things right. It also seems to me like I need to make up my mind pretty much immediately if I want to be able to claim that I'm acting in good faith.

Yes. I agree. You should be at liberty and authority to either accept the contract as is or reject it and negotiate for what you want. You're not an indentured servant.

What are my options in this situation?

I'd say your options are to either accept the contract as is or reject it and negotiate for what you want. The agency and the client are then at liberty to negotiate with you or terminate your contract.

First: I'm probably in his address book, so my messages won't go to Junk.

You being in his contacts doesn't mean that your email won't end up in his junk folder. Contacts aren't automatically considered "safe senders".

He had no trouble receiving my emails a few months ago, when I had a problem at the client and asked for his help.

As is the nature of email and spam filtering. Things change every day. Spammers change their tactics and methods and spam filters change to stay at pace with those tactics and methods. What went to the Inbox today may very well end up in the Junk folder tomorrow.

I think it's known that this client does not like to give out raises, and so I suspect that he saw my email asking to negotiate for a raise, worried that it would derail an otherwise guaranteed renewal, and decided to duck my messages until all the paperwork was filed, hoping to make it a fait accompli. It's also a little suspicious that I got no response from any of my other contacts at the agency -- this makes me think they're closing ranks to help this shady gambit succeed.

If your email wound up in his junk folder then it's almost guaranteed that it wound up in the junk folder of everyone else at the agency. I don't find this particularly unusual or suspect.

It seems to me like I am at liberty to reject the agreement entirely, because it was made without my authorization or even my knowledge, and that it's up to me whether to give the recruiter any option to make things right. It also seems to me like I need to make up my mind pretty much immediately if I want to be able to claim that I'm acting in good faith.

Yes. I agree. You should be at liberty and have the authority to either accept the contract as is or reject it and negotiate for what you want. You're not an indentured servant.

What are my options in this situation?

I'd say your options are to either accept the contract as is or reject it and negotiate for what you want. The agency and the client are then at liberty to negotiate with you or terminate your contract.