What should I have the customer sign for me the general contractor if she terminates me for convenience

I’m a general contractor in California. Customer has decided to terminate me for convenience(clause included in contract) It seems I should get her to sign some sort of agreement that she has in fact terminated for convenience rather than for cause What sort of agreement? And can this include some sort of waiver of responsibilty for the contractor to complete job, and/or waiver of liability for work completed? Thank you