refactor(git): older-on-left placement, drop empty placeholders

lua/git/object.lua

@@ -275,19 +275,24 @@ function M.read_uri(buf)
     vim.api.nvim_exec_autocmds("BufReadPost", { buffer = buf })
 end
 
----Buffer for the file at `<ref>:<path>`. A zero/nil blob (file absent on
----this side of the diff) yields an empty placeholder.
+---Buffer for the file at `<ref>:<path>`. A zero/nil blob (file absent
+---on this side of the diff) maps to `/dev/null`, mirroring git's diff
+---headers.
 ---@param worktree string
 ---@param blob string?
 ---@param path string
 ---@param ref string  the commit ref the blob represents (e.g. `<sha>` or `<sha>^`)
 ---@return integer
 local function blob_buf(worktree, blob, path, ref)
-    local revspec = ref .. ":" .. path
     if is_zero(blob) then
-        return util.empty_buf({ name = util.uri(revspec) })
+        local buf = vim.fn.bufnr("/dev/null")
+        if buf == -1 then
+            buf = vim.api.nvim_create_buf(true, true)
+            pcall(vim.api.nvim_buf_set_name, buf, "/dev/null")
+        end
+        return buf
     end
-    return M.buf_for(worktree, revspec)
+    return M.buf_for(worktree, ref .. ":" .. path)
 end
 
 ---@param worktree string
@@ -308,8 +313,6 @@ local function open_section(ctx, section)
         return
     end
     local parent = ctx.parent_ref or "0"
-    -- An empty buffer for zero blobs keeps `:diffsplit` from
-    -- BufReadCmd-loading a non-existent revspec.
     local left =
         blob_buf(ctx.worktree, section.pre_blob, section.pre_path, parent)
     local right =