chore(git): consistent error reporting on git failures

lua/git/cmd.lua

@@ -20,15 +20,17 @@ local cached_cmds
 
 ---@param result vim.SystemCompleted
 local function populate_cached_cmds(result)
-    cached_cmds = {}
-    if result.code == 0 then
-        for line in (result.stdout or ""):gmatch("[^\r\n]+") do
-            if line ~= "" then
-                table.insert(cached_cmds, line)
-            end
-        end
-        table.sort(cached_cmds)
+    if result.code ~= 0 then
+        log.error("git --list-cmds failed: %s", vim.trim(result.stderr or ""))
+        return
     end
+    cached_cmds = {}
+    for line in (result.stdout or ""):gmatch("[^\r\n]+") do
+        if line ~= "" then
+            table.insert(cached_cmds, line)
+        end
+    end
+    table.sort(cached_cmds)
 end
 
 ---Prime `cached_cmds` asynchronously so the first `:G <Tab>` doesn't block.
@@ -111,6 +113,13 @@ local function run_in_split(worktree, args, conf)
             vim.api.nvim_buf_set_lines(buf, 0, -1, false, split_lines(content))
             vim.bo[buf].modifiable = false
             vim.bo[buf].modified = false
+            if obj.code ~= 0 then
+                log.error(
+                    "git %s failed: %s",
+                    args[1] or "",
+                    vim.trim(obj.stderr or "")
+                )
+            end
         end)
     end)
 end