refactor(git): load git:// URI buffers via BufReadCmd

lua/git/cmd.lua

@@ -68,10 +68,39 @@ local function first_positional(args, start)
     end
 end
 
+---Open `<ref>:<path>` in a split via the `git://` BufReadCmd loader.
+---Resolves to a sha first so the URI stays stable if the ref moves.
+---@param worktree string
+---@param user_ref string
+---@param path string
+local function show_file_in_split(worktree, user_ref, path)
+    repo.rev_parse(worktree, user_ref, true, function(sha)
+        local label = sha or user_ref
+        local uri = "git://" .. label .. "//" .. path
+        local buf = vim.fn.bufadd(uri)
+        vim.b[buf].git_worktree = worktree
+        vim.cmd("split " .. vim.fn.fnameescape(uri))
+    end)
+end
+
 ---@param worktree string
 ---@param args string[]
 ---@param conf ow.Git.SplitHandler
 local function run_in_split(worktree, args, conf)
+    -- `<ref>:<path>` is a file lookup; the URI must carry the path so
+    -- filetype detection has something to match against.
+    if args[1] == "show" then
+        local arg = first_positional(args, 2)
+        if arg then
+            local ref, path = arg:match("^(.-):(.+)$")
+            if ref then
+                ---@cast path -nil
+                show_file_in_split(worktree, ref, path)
+                return
+            end
+        end
+    end
+
     local buf = git.new_scratch()
     vim.b[buf].git_worktree = worktree
     if conf.needs_ref then
@@ -80,7 +109,7 @@ local function run_in_split(worktree, args, conf)
             if not vim.api.nvim_buf_is_valid(buf) then
                 return
             end
-            pcall(vim.api.nvim_buf_set_name, buf, "git://" .. label .. "/")
+            pcall(vim.api.nvim_buf_set_name, buf, "git://" .. label .. "//")
             vim.bo[buf].filetype = conf.ft
         end
         repo.rev_parse(worktree, user_ref, true, function(sha)