Thanks a lot.
I found that keymapping “after” OhMyREPL does not properly work.
So I moved lines about keymapping at the beginning of startup.jl as follows, and it works.
import REPL
import REPL.LineEdit: MIState, edit_delete_prev_word, ModeState
atreplinit() do repl
repl.interface = REPL.setup_interface(repl; extra_repl_keymap = Dict("^W" => "\e\b"))
end
Reference: Customizing-keybindings