refactor(git): bracket-named scratches for :G, reuse on re-run

lua/git/cmd.lua

@@ -109,8 +109,32 @@ local function run_in_split(worktree, args, conf)
         end
     end
 
-    local buf = git.new_scratch()
+    -- Bracket naming so the buffer name doesn't pretend to be a real
+    -- file path (and doesn't collide with the `git://<revspec>` URI
+    -- form used by the BufReadCmd loader). Reused on re-run so a
+    -- second `:G show HEAD` refreshes the existing buffer in place
+    -- instead of leaving a nameless duplicate behind.
+    local name = "[git " .. table.concat(args, " ") .. "]"
+    local buf = vim.fn.bufnr(name)
+    if buf == -1 or not vim.api.nvim_buf_is_loaded(buf) then
+        buf = git.new_scratch()
+        pcall(vim.api.nvim_buf_set_name, buf, name)
+    else
+        local win_id = vim.fn.bufwinid(buf)
+        if win_id ~= -1 then
+            vim.api.nvim_set_current_win(win_id)
+        else
+            vim.api.nvim_open_win(buf, true, {
+                split = vim.o.splitbelow and "below" or "above",
+            })
+        end
+        vim.bo[buf].modifiable = true
+        vim.api.nvim_buf_set_lines(buf, 0, -1, false, {})
+    end
+
     vim.b[buf].git_worktree = worktree
+    vim.b[buf].git_ref = nil
+    vim.b[buf].git_parent_ref = nil
     if conf.needs_ref then
         local user_ref = first_positional(args, 2) or "HEAD"
         local sha = repo.rev_parse(worktree, user_ref, true)
@@ -119,17 +143,8 @@ local function run_in_split(worktree, args, conf)
             vim.b[buf].git_parent_ref =
                 repo.rev_parse(worktree, user_ref .. "^", true)
         end
-        -- Per-subcommand scheme so `:G show <sha>` doesn't collide with
-        -- the cat-file URI form `git://<sha>` used by the gitlog flow.
-        pcall(
-            vim.api.nvim_buf_set_name,
-            buf,
-            "git" .. args[1] .. "://" .. (sha or user_ref)
-        )
-        vim.bo[buf].filetype = conf.ft
-    else
-        vim.bo[buf].filetype = conf.ft
     end
+    vim.bo[buf].filetype = conf.ft
 
     local cmd = { "git" }
     vim.list_extend(cmd, args)