Great!

I've looked at the replxx from this PR and here a few bits:

• CTRL-J does not works as ENTER, this can be fixed by adding a custom bind in

  ClickHouse/base/base/ReplxxLineReader.cpp

  Line 178 in a163230

  rx.bind_key(Replxx::KEY::control('N'), [this](char32_t code) { return rx.invoke(Replxx::ACTION::HISTORY_NEXT, code); });

• it does not reads correctly multiline comments from the existing history files (I remember that you've mentioned something about multiline format changes), I guess it is ok, but maybe if it is simple enough than it can be added to

  ClickHouse/base/base/ReplxxLineReader.cpp

  Line 61 in a163230

  void convertHistoryFile(const std::string & path, replxx::Replxx & rx)

  although I'm not sure

it does not reads correctly multiline comments from the existing history files (I remember that you've mentioned something about multiline format changes), I guess it is ok,

I think we should use the upstream's behavior. Add the conversion will be expensive for large history files (we will need to check the file everytime)