Scope branch refresh fetch to checked-out upstream refspec

- derive upstream branch from `branch@{upstream}` and guard empty values
- fetch only `+refs/heads/<branch>:refs/remotes/<remote>/<branch>` instead of all remote refs
- add integration test asserting scoped fetch args during `checkoutBranch`
6708fe996aJulius Marminge committed on 2/15/2026, 8:53:20 AM· committed by Julius Marmingeparent72d7fcc
2 files changedLine totals unavailable