Code review? What CODE will allow you to verify which of two chains is the best if not using criteria that longest chain is best chain.
Please, do not mix up things. As I told you, we need to separate issues first.
Code review is necessary to ensure, you have the 'right' checkpoints (including the genesis block - for those who cannot imagine the genesis block hard-coded in the node software being a checkpoint), the right consensus rule that everybody has, etc. etc.
In particular the checkpoints are the ones that determine which chains will definitely being sorted out and which ones could win in the future.
Verification? What can you verify to determine which chain is the best if not using the criteria that the longest chain is the best chain.
etc?
See above. Checkpoints are a valid way to do so. A node provider could even introduce custom checkpoints at will.
Give me specifics. You are a brand new node bootstraping today you receive from peers two equally valid yet different chains A & B. The code in the client can be assumed to be without error. Chain A is longer, thus by the Bitcoin consensus rules a Bitcoin node would report that Chain A is the best chain. You seem to believe that nodes could reach a consensus that B the shorter chain is "best". How exactly would a new node reach that conclusion. Without specifics that is simply imagining the problem away. Some magical as of yet code will allow the client to pick Chain B because it is the better chain despite being shorter is not a real answer. What exactly could the new node do to determine that B is the better chain over A?
There is nothing wrong with this rule.
I think you agree that the coins on a fork are worthless to the real world. There can be only one legit chain. So, the real world decides that in the end. The real world are people, exchanges, friends and so on. If my node has two valid chains, I will consult them to find out which one it the right one.
What is wrong with that consensus rule? After that, I am on the same "fork" as the rest of the publicly available world is. I am on the same "fork" where the rest of the publicly available world draws its value from the coin.