I-129 is company's A petition - -you are just a beneficiary in it. Company B needs to file a new petition. This is setting aside the moral aspect of you acting dishonestly toward company A
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You are assuming the currently filed H-1b will be accepted and approved. Both are unsafe assumptions.
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No, you don't transfer your H1b to an employer whom you never worked for. Instead, the new employer files a new H1b based upon the originsl I-94 provided the EAD is still valid. If expired, or out of status, then you 'may' have to consular process the second H1 B visa petition without a change of status.
I strongly recommend an appointment with a competent and experienced immigration and visa attorney before you do anything more. Good luck.
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