Three follow-up fixes — all the same shape: silently doing the wrong
thing instead of either honoring --branch or refusing.
1) --check --branch <missing> raised CalledProcessError from
'git rev-list ... --count' (check=True) when the branch didn't
exist on origin. 'git fetch origin' succeeds without a refspec
(it just fetches what's there), so the bad-branch case wasn't
caught at the fetch step. Now verify the compare ref with
'git rev-parse --verify --quiet' before rev-list and emit a
friendly error.
2) _update_via_zip (Windows fallback for broken git file I/O)
hard-coded branch = 'main', so on the ZIP path --branch=foo
silently downloaded main.zip and told the user it worked. Refuse
in that case instead — silently lying about which branch got
installed is exactly what --branch was added to prevent.
3) _cmd_update_check PyPI path returned before looking at branch,
so PyPI users running 'hermes update --check --branch=x' got a
generic PyPI version check with no indication --branch was
dropped. Now prints a one-line warning when --branch was explicit
and non-main.
Also pull the '(getattr(args, branch, None) or main).strip() or main'
expression into _resolve_update_branch(args) — three callsites agree
on the same parsing.
Tests: 5 new tests for the --check + --branch matrix (named branch,
missing branch, default-main upstream-first, PyPI warning) and the
ZIP refusal. test_cmd_update.py is 20/20 green, broader hermes_cli/
suite (4952 tests) unchanged.
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