Re: Do wallets detect fork and warn for it?

We need functional and fully trustable non-full clients or else we die.

We do. its called Electrum.

Huh, did you were here a couple days ago? All SPV wallets suffered from a high risk of non valid transactions due the blockchain split, and guess what, Electrum is a SPV wallet. Basically any wallet that wasn't an updated core wallet was under risk.

You: We need non-full clients.
Me: There are some.
You: But they aren't full clients.

SPV wallets can't be fully trusted as seen 2 days ago.

Nothing can ever be "fully trusted" except your own node if you want to take that thinking to its logical conclusion.
However, for most of the time and especially smaller payments, SPV works great.