What are the steps to legally work in Thailand after arriving on a spouse O visa while on a job contract?

In theory <- NOTE I said that, you could get an extension based on being married to someone who legally works here, then get paperwork from your company, cancel your extension based on marriage to a foreigner and immediately apply for a new extension based on employment. BUT I have only seen people be able to pull it off a couple times because it all has to be done on the same day and it takes coordination from the company you got the first extension on and the one you're getting the new extension on. It can be done, BUT it's rare.

Honestly, I'd say get the documentation together to go get a 90 day single entry Non-B visa from a thai consulate in a nearby country (Make SURE you check their website to have the correct documentation as each consulate is slightly different) and just go get one in another country.

If you are on a Non-Immigrant Type O visa based on being married to a foreigner that legally works here you CANNOT hold a work permit on it.

Also IF you're on the initial 90 day entry of that visa you can't convert it to a different type of visa inside the country. You would have to leave the country and get a 90 day single entry Non-B <- business visa from a nearby thai consulate.

I hope I understand this. You have a Non Immigrant O visa as dependent on your wife who works in Thailand, but her company does not want to give you the needed papers needed for Extension of Stay or new Visa. The best way now is to let your employer apply for the Work Permit, with the papers from company and Work Permit application approved you visit a Thai Consulate or Embassy and apply for the Non Immigrant B visa for yourself.