git switch -c / git checkout -b from the current branch record
'branch: Created from HEAD' in the reflog, but parseBranchCreationSource
only rejected 'HEAD@{...}' (detached start) and raw commit hashes. The
bare HEAD passed through, so getBranchBase returned { base: 'HEAD' }
and the branch scope computed diffs against HEAD itself, which is empty
when the service is checked out on that branch and wrong otherwise.
Treat bare HEAD like HEAD@{...}: no named source is recorded, so return
null and let the UI ask the user to pick a base.
gaojunran
a498d1935d