Not a lawyer, probably wrong, but: California's courts won't enforce a contract not recognized by California law, but the courts of other states will, and it will depend on whether the employer can get personal jurisdiction for the case in the right state.

The short answer is: in your situation, you'd need a lawyer.

(I think --- not sure, not an authority --- that the "incorporation in Delaware" part of this has minimal impact; your residence in North Carolina, and the firm's operations in California, are probably the big two salient facts).

I think North Carolina is similar to California wrt work on your own time not relaTed to employers line of work.

I work remote for a large SF Bay Area firm from NC.