An NDA is enforceable in California. An NCA is not.
Although there may be issues connected to your question that could be tested in court, the principal difficulty confronting your current employer is that while it may be able prevent you
from competing directly against your current employer, it cannot prevent your new employer
from competing, because that employer has no NCA contract with your current employer.
So, the issue devolves into questions about the exact language of your current NCA, and your job description for the new employer. Your current NCA would have to state that you cannot work for a new employer in any capacity, if that employer competes with your current employer. The question for a court would be whether or not your activities for the new employer actually represented competition for the current employer, and if so, whether or not that competition was sufficiently injurious to warrant an injunction against your continued employment.
Also, it would be necessary that your current employer discover that you are employed by a competitor, and then determine that your employment represents a genuine threat of lost business. This is not always easily accomplished.
The point is that a lawsuit against you is a non-trivial and extremely costly exercise both for the plaintiff and defendant. Were it me, I would not accept employment with the new employer unless that employer agreed to indemnify me against the cost of defending a legal action against the current employer. Otherwise, even if you are ultimately sued and you prevail, you could burn through a year's salary defending yourself.
Hope this helps.
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