local function split_sentences()
    local view = vim.fn.winsaveview() -- keep cursor & view stable
    vim.cmd([[%s/\([.?!]\)\s\+/\1\r/ge]])
    vim.fn.winrestview(view)
end

-- run after leaving insert mode
vim.api.nvim_create_autocmd({ "InsertLeave", "TextChanged" }, {
    pattern = { "*.md", "*.txt" },
    callback = split_sentences
})