feat(git): navigate any git object from cat-file headers

lua/git/cmd.lua

@@ -119,7 +119,13 @@ local function run_in_split(worktree, args, conf)
             vim.b[buf].git_parent_ref =
                 repo.rev_parse(worktree, user_ref .. "^", true)
         end
-        pcall(vim.api.nvim_buf_set_name, buf, "git://" .. (sha or user_ref))
+        -- 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

lua/git/object.lua

@@ -115,18 +115,21 @@ local function show_diff(ctx, section)
         return
     end
     local parent = ctx.parent_ref or "0"
+    -- blob_buf handles the absent (zero-blob) case by returning an empty
+    -- buffer, which keeps `:diffsplit` from triggering BufReadCmd against
+    -- a non-existent revspec and logging an error.
     local left =
         blob_buf(ctx.worktree, section.pre_blob, section.pre_path, parent)
     local right =
         blob_buf(ctx.worktree, section.post_blob, section.post_path, ctx.ref)
     vim.cmd.normal({ "m'", bang = true })
-    local left_win = vim.api.nvim_get_current_win()
-    vim.api.nvim_set_current_buf(left)
-    vim.wo[left_win].diff = true
-    local right_win =
-        vim.api.nvim_open_win(right, true, { split = "right", win = left_win })
-    vim.wo[right_win].diff = true
-    vim.api.nvim_set_current_win(left_win)
+    vim.api.nvim_set_current_buf(right)
+    -- `:diffsplit` is the same path `M.split` uses; Vim's built-in diff
+    -- machinery handles the diff option setup on both windows.
+    vim.cmd(
+        "leftabove vert diffsplit "
+            .. vim.fn.fnameescape(vim.api.nvim_buf_get_name(left))
+    )
 end
 
 ---@class ow.Git.OpenCommitOpts
@@ -265,7 +268,8 @@ function M.open_under_cursor()
     -- Cat-file header navigation: `parent <sha>` (commit), `tree <sha>`
     -- (commit / tag), `object <sha>` (tag's referent) all reference
     -- another git object.
-    local sha = line:match("^parent (%x+)$")
+    local sha = line:match("^commit (%x+)$")
+        or line:match("^parent (%x+)$")
         or line:match("^tree (%x+)$")
         or line:match("^object (%x+)$")
     if sha then