`hermes update` has always hard-coded its target to `main`. Add --branch
so callers can update against a non-default channel while preserving every
existing behavior at the default:
- `hermes update` still pulls main (no behavior change)
- `hermes update --branch X` pulls origin/X, auto-stashing and switching
local HEAD to X first if needed
- `hermes update --check --branch X` reports behindness against
origin/X (and skips the upstream/X probe,
since forks don't have upstream copies of
their own feature branches)
- Branch absent locally → retry as `checkout -B X origin/X` (track)
- Branch absent everywhere → exit 1 with a clear error, after restoring
the user's prior stash so we don't strand
them in a weird state
The fork-upstream sync logic was already guarded on `branch == 'main'`,
so non-main updates correctly skip the upstream trampling without
further changes.
5 new tests cover: explicit --branch, default-to-main, switch-from-other,
track-from-origin, and the fail-cleanly case. Full test_cmd_update.py
suite (15 tests) passes on main.
51689a4206