But I purposely didn't mention the Havana sequence b/c I think that
Fredo's treachery ends with the botched Tahoe attempt*. I don't think he had any
direct involvement in Roth's Havana plan or any plans thereafter the time of the Tahoe shooting. After all, he told Johnny Ola not to call him anymore. Remember?

I am not so sure that Fredo did as Michael asked of him.
Fredo: How can I help Mike?
Michael: Act as if you know nothing.
While I agree that Fredo knew it was going to be a hit, after the attempt failed, I think he was probably kept in the dark by Roth and Ola.
I think he may have warned Roth about hit before the New Year.