refactor(git): convert blocking subprocess calls to async

lua/git/init.lua

@@ -25,6 +25,33 @@ function M.head(path)
     return repo.head(path)
 end
 
+---@class ow.Git.NewScratchOpts
+---@field name string?
+---@field bufhidden ("hide"|"wipe")?  defaults to "hide"
+---@field split ("above"|"below"|"left"|"right")?  defaults to splitbelow-aware horizontal
+
+---Open a split with a fresh non-modifiable scratch buffer. Default split
+---direction is horizontal, honouring `splitbelow`. Caller flips
+---`modifiable`, fills the buffer, and sets `filetype` once content lands.
+---@param opts ow.Git.NewScratchOpts?
+---@return integer buf
+---@return integer win
+function M.new_scratch(opts)
+    opts = opts or {}
+    local buf = vim.api.nvim_create_buf(false, true)
+    vim.bo[buf].buftype = "nofile"
+    vim.bo[buf].bufhidden = opts.bufhidden or "hide"
+    vim.bo[buf].swapfile = false
+    vim.bo[buf].modifiable = false
+    vim.bo[buf].modified = false
+    if opts.name then
+        pcall(vim.api.nvim_buf_set_name, buf, opts.name)
+    end
+    local split = opts.split or (vim.o.splitbelow and "below" or "above")
+    local win = vim.api.nvim_open_win(buf, true, { split = split })
+    return buf, win
+end
+
 function M.setup()
     for name, link in pairs(HIGHLIGHTS) do
         vim.api.nvim_set_hl(0, name, { link = link, default = true })