How would H1B extension bridge application affect H1B transfer

Hi Anil,
Currently, I am working for an Employer A on an H1B visa, and my I94 is valid until 08/31/2020. I got an offer last week from Employer B as per the plan, Employer B supposed to file an H1B petition with premium processing.

Still, premium processing is in suspension state, and Employer B policy allows an employee to start working after the H1B receipt is received. (estimated start date on the offer letter will be June 1st, as they would apply for premium processing in meanwhile if USCIS resume back).

In a worst-case scenario, if premium processing is not resumed again, I would need to join the Employer B on the received receipt notice, after giving employer A a formal three weeks’ notice.

In case if current Employer A will put a request to revoke my H1B on the next day of my formal notice received.

Should I be legally okay to stay in the country with the receipt number & offer letter (June 1st), or, I’ll have to request Employer B for an early start date offer to start work.

And I will NOT have to travel outside the US during the H1b transfer approval is pending with Employer B? Can you please confirm?