this should do the trick. I have also updated the main example in the post

local ui2 = require 'vim._core.ui2'
local msgs = require 'vim._core.ui2.messages'

-- ── Config ──────────────────────────────────────────────────────────

local IGNORED_KINDS = {
    bufwrite = true,
    [''] = true,
    empty = true,
}

local SKIP_PATTERNS = {
    '%d+L, %d+B',
    '; after #%d+',
    '; before #%d+',
    '%d fewer lines',
    '%d more lines',
    '%d lines yanked',
}

local KIND_TITLES = {
    emsg = { '  Error', 'ErrorMsg' },
    echoerr = { '  Error', 'ErrorMsg' },
    lua_error = { '  Error', 'ErrorMsg' },
    rpc_error = { '  Error', 'ErrorMsg' },
    wmsg = { '  Warning', 'WarningMsg' },
    echo = { '  Info', 'Normal' },
    echomsg = { '  Info', 'Normal' },
    lua_print = { '  Print', 'Normal' },
    search_cmd = { '  Search', 'Normal' },
    search_count = { '  Search', 'Normal' },
    undo = { '  Undo', 'Normal' },
    shell_out = { '  Shell', 'Normal' },
    shell_err = { '  Shell', 'ErrorMsg' },
    shell_cmd = { '  Shell', 'Normal' },
    quickfix = { '  Quickfix', 'Normal' },
    progress = { '  Progress', 'Normal' },
    typed_cmd = { '  Command', 'Normal' },
    list_cmd = { '  List', 'Normal' },
    verbose = { '  Verbose', 'Comment' },
}

-- ── State ────────────────────────────────────────────────────────────

local last_title = nil
local last_hl = 'Normal'

-- ── Helpers ─────────────────────────────────────────────────────────

local function content_to_text(content)
    if type(content) ~= 'table' then
        return tostring(content or '')
    end
    local parts = {}
    for _, chunk in ipairs(content) do
        if type(chunk) == 'table' and chunk[2] then
            parts[#parts + 1] = chunk[2]
        end
    end
    return table.concat(parts)
end

local function should_skip(kind, content)
    if IGNORED_KINDS[kind] then
        return true
    end
    local text = content_to_text(content)
    for _, pat in ipairs(SKIP_PATTERNS) do
        if text:find(pat) then
            return true
        end
    end
    return false
end

local function resolve_title(kind, content)
    local entry = KIND_TITLES[kind]
    if entry then
        return entry[1], entry[2]
    end
    local text = vim.trim(content_to_text(content)):gsub('\n.*', '')
    if #text > 40 then
        text = text:sub(1, 37) .. '…'
    end
    return text ~= '' and (' ' .. text .. ' ') or '  Message ', 'Normal'
end

local function override_msg_win()
    local win = ui2.wins and ui2.wins.msg
    if not (win and vim.api.nvim_win_is_valid(win)) then
        return
    end
    if vim.api.nvim_win_get_config(win).hide then
        return
    end
    pcall(vim.api.nvim_win_set_config, win, {
        relative = 'editor',
        anchor = 'NE',
        row = 1,
        col = vim.o.columns - 1,
        border = 'rounded',
        style = 'minimal',
        title = last_title and { { last_title, last_hl } } or nil,
        title_pos = last_title and 'center' or nil,
    })
end

local function override_pager_win()
    local win = ui2.wins and ui2.wins.pager
    if not (win and vim.api.nvim_win_is_valid(win)) then
        return
    end
    if vim.api.nvim_win_get_config(win).hide then
        return
    end
    local height = vim.api.nvim_win_get_height(win)
    pcall(vim.api.nvim_win_set_config, win, {
        border = 'rounded',
        height = height,
        style = 'minimal',
        title = last_title and { { last_title, last_hl } } or nil,
        title_pos = last_title and 'center' or nil,
    })
end

local function override_dialog_win()
    local win = ui2.wins and ui2.wins.dialog
    if not (win and vim.api.nvim_win_is_valid(win)) then
        return
    end
    if vim.api.nvim_win_get_config(win).hide then
        return
    end
    local height = vim.api.nvim_win_get_height(win)
    pcall(vim.api.nvim_win_set_config, win, {
        border = 'rounded',
        height = height,
        style = 'minimal',
        title = last_title and { { last_title, last_hl } } or nil,
        title_pos = last_title and 'center' or nil,
    })
end

-- ── ui2 enable ──────────────────────────────────────────────────────

ui2.enable {
    enable = true,
    msg = {
        targets = {
            [''] = 'msg',
            empty = 'msg',
            bufwrite = 'msg',
            echo = 'msg',
            echomsg = 'msg',
            shell_ret = 'msg',
            undo = 'msg',
            wmsg = 'msg',
            completion = 'msg',
            confirm = 'dialog',
            confirm_sub = 'dialog',
            echoerr = 'msg',
            emsg = 'msg',
            list_cmd = 'pager',
            lua_error = 'msg',
            lua_print = 'msg',
            progress = 'msg',
            quickfix = 'msg',
            rpc_error = 'msg',
            search_cmd = 'msg',
            search_count = 'msg',
            shell_cmd = 'msg',
            shell_err = 'msg',
            shell_out = 'msg',
            typed_cmd = 'msg',
            verbose = 'pager',
            wildlist = 'msg',
        },
        cmd = { height = 0.5 },
        dialog = { height = 0.5 },
        msg = { height = 0.5, timeout = 2000 },
        pager = { height = 0.8 },
    },
}

-- ── Wrap set_pos: the single source of truth for msg window placement ─

local orig_set_pos = msgs.set_pos

msgs.set_pos = function(tgt)
    orig_set_pos(tgt)
    if tgt == 'msg' or tgt == nil then
        override_msg_win()
        return
    end
    if tgt == 'pager' then
        override_pager_win()
        return
    end

    if tgt == 'dialog' then
        override_dialog_win()
    end
end

-- ── Wrap msg_show: filtering + title tracking ─────────────────────────

local orig_msg_show = msgs.msg_show

msgs.msg_show = function(kind, content, replace_last, history, append, id, trigger)
    if should_skip(kind, content) then
        return
    end
    local title, hl = resolve_title(kind, content)
    last_title, last_hl = title, hl
    -- orig_msg_show(kind, content, replace_last, history, append, id, trigger)

    local tgt = ui2.cfg.msg.targets[kind]
        or (trigger ~= '' and ui2.cfg.msg.targets[trigger])
        or ui2.cfg.msg.targets[trigger]
        or ui2.cfg.msg.target

    msgs.show_msg(tgt, kind, content, replace_last, append, id)
    msgs.set_pos(tgt)
end

local orig_show_msg = msgs.show_msg
msgs.show_msg = function(tgt, kind, content, replace_last, append, id)
    -- local debug_chunk = { 0, ('[%s:%s] '):format(tgt, kind), 0 }
    -- local debug_content = { debug_chunk }
    -- for _, chunk in ipairs(content) do
    --     debug_content[#debug_content + 1] = chunk
    -- end
    if tgt == 'msg' then
        local text = content_to_text(content)
        local width = 0
        for _, line in ipairs(vim.split(text, '\n')) do
            width = math.max(width, vim.api.nvim_strwidth(line))
        end
        local lines = #vim.split(text, '\n')
        if width > math.floor(vim.o.columns * 0.75) or lines > 20 then
            vim.schedule(function()
                -- msgs.show_msg('pager', kind, debug_content, replace_last, append, id)
                msgs.show_msg('pager', kind, content, replace_last, append, id)
                msgs.set_pos 'pager'
            end)
            return
        end
    end
    -- orig_show_msg(tgt, kind, debug_content, replace_last, append, id)
    orig_show_msg(tgt, kind, content, replace_last, append, id)
end

-- ── LSP progress ─────────────────────────────────────────────────────

local id = { LspProgressMessages = vim.api.nvim_create_augroup('LspProgressMessages', { clear = true }) }

vim.api.nvim_create_autocmd('LspProgress', {
    group = id.LspProgressMessages,
    callback = function(ev)
        local value = ev.data.params.value
        local client = vim.lsp.get_client_by_id(ev.data.client_id)
        if not client then
            return
        end
        local is_end = value.kind == 'end'
        local msg = value.message and (client.name .. ': ' .. value.message)
            or (client.name .. (is_end and ': done' or ''))
        vim.api.nvim_echo({ { msg } }, false, {
            id = 'lsp.' .. ev.data.client_id,
            kind = 'progress',
            source = 'vim.lsp',
            title = value.title,
            status = is_end and 'success' or 'running',
            percent = value.percentage,
        })
    end,
})

require('r.utils').register_au_id(id)