On: I'm leaving my day job. But my CEO doesn't want me to leave.

IANAL, but I don't know that you have to sign any kind of agreement other than you cashing your paychecks and them having a written policy stashed away somewhere.

Note to self: determine if they have any IP policy stashed away somewhere.

The startup existed as its own corporation before they hired me; in fact, they hired me because they liked the startup.