Not sure how much this matters in California, but this rule is usually iron-clad. The first few sentences explain:
There is a general rule in California barring the assignment of a cause of action for legal malpractice. In this case, we recognize a narrow exception to that rule. Specifically, a cause of action for legal malpractice is transferable when (as here): (1) the assignment of the legal malpractice claim is only a small, incidental part of a larger commercial transfer between insurance companies; (2) the larger transfer is of assets, rights, obligations, and liabilities and does not treat the legal malpractice claim as a distinct commodity; (3) the transfer is not to a former adversary; (4) the legal malpractice claim arose under circumstances where the original client insurance company retained the attorney to represent and defend an insured; and (5) the communications between the attorney and the original client insurance company were conducted via a third party claims administrator.
White Mountains Reinsurance Co. of Am. v. Borton Petrini, LLP, C071365, 2013 WL 6181126 (Cal. Ct. App. Nov. 26, 2013)