The arrest will be on your record, yes. Disclosure will depend on the question asked. If directly asked about past arrests or prosecutions, then you would have to disclose or face penalties ranging from internal discipline or termination, up to prosecution for perjury if appropriate. I should add that a perjury prosecution would be very rare in this circumstance, but the possibility could be there. Honesty typically is the best policy, but you should discuss licensing and employment issues with someone well versed in thaose particular areas.
Removing this from your record will be difficult. You may pursue a factual innocence finding, but that is a low percentage proposition and will almost certainly require a lawyer's services to have any hope at all.
You should probably speak to an attorney local to the court of prosecution. This type of disposition is very unusual, especially mid-prelim. I would certainly want to see the court records to confirm that this disposition went down as you relate, and also to assess your options at this point.
Any statements I make in these forums (fora?) should not be taken as direct legal advice, merely informed guidance. This is true due to the anonymous nature of this venue, and the incomplete information which is invariably provided by the questions. It is imperative that you consult directly with an attorney regarding your specific situation before acting on or relying on anything represented here. Period.
Most applications don't ask about arrests, but if they do ask about arrests, then you have to disclose it. The time limit for petitioning for factual innocence is 2 years, so that is not an option, unless you have extraordinary circumstances to explain why you didn't petition earlier. Regardless, it doesn't sound like you could prove your factual innocence anyway, so that would be a dead issue. Best of luck to you.
I concur with Mr. Moore's very sound summary, and I write to add these considerations about the state licensing process:
That there is some variation among CA licensing agencies as to the scope of disclosure that is required by the various licensing applications. However, all CA licensing agencies will use your Live Scan Report and will follow-up with demands for additional disclosure of all facts and circumstances as to all matters that appear on the Live Scan -- even where the info was not by the terms of the application required to be addressed on the application. And in almost all instances, such follow-up investigation is allowed by law, even where there was no conviction.
Because of deep staff cuts in the State workforce, it can take approximately 2 years for an application requiring even minimal follow-up investigation to be acted upon by the licensing agency. One strategy that can be effective, depending on the scope of the applicant's criminal history, is to order a personal copy of the Live Scan (very cheap, very fast: Google for how to) and to take the initiative to disclose on the license application the facts and circumstances for all the Live Scan entries, even where the application does not specifically require. This strategy can best be used where the applicant has consulted licensing counsel and can determine with certainty what criminal history data will be subject to follow-up investigation and demand for disclosure by the agency.
It is important to make all errors on the side of disclosure. CA licensing agencies are irrationally harsh and narrow in their reactions to any -- ANY -- failures to disclose, and they have heard every conceivable explanation thousands of times. It can be nearly impossible to dig out of a determination by the State that the obligation for full disclosure was breached. A determination by the State that matter that should have been disclosed was not disclosed, or not fully disclosed, will be a severe and long-term obstacle for State licensing, far more preclusive than almost any underlying prior criminal history.
My responses to questions on Avvo are never intended as legal advice and must not be relied upon as legal advice. I give legal advice only in the course of an attorney-client relationship. Exchange of information through Avvo's Questions forum does not establish an attorney-client relationship with me. That relationship is established only by individual consultation and execution of a written agreement for legal services.