Mason's ruby-lsp is a gem bound to whichever Ruby installed it. In a
project that pins a different Ruby, loading the project bundle fails
with Bundler::RubyVersionMismatch and the server exits, which is what
kept producing the client-quit warning. ruby-lsp's editor docs advise
against Mason for this reason and recommend the version manager's
shim.
Turn Mason off for ruby_lsp and launch ~/.rbenv/shims/ruby-lsp from
the project root, since rbenv resolves .ruby-version from the working
directory and Neovim otherwise starts servers in its own cwd. Machines
without rbenv fall back to ruby-lsp on PATH.
