Mostly a rubber-stamp, particularly the tests I just skimmed.
It's also a common fix just with unsafe-options guards, and
a regex fix which hopefully is truly better than before.
I didn't question it in the interest of time.

<!-- agent -->
Address GHSA-w8jc-g24h-crhw by applying the existing guard policy to
`Git.ls_remote()`, `Repo.merge_base()`, and `IndexFile.move()`. These wrappers
previously omitted protocol or option checks already used by sibling APIs.

Check flattened positional arguments and split short-option values before
`ls_remote()` starts Git, including values that become the repository after
option parsing. Add the independent `allow_unsafe_protocols` opt-in and recognize
helper selectors even when their address is empty or begins with a newline.
Match Git's scheme-character rules at the start of the address so ordinary
IPv6 URLs and double colons in repository paths retain their meaning. This
addresses the review finding that the broad matcher rejected valid IPv6 remotes.
The protocol check is conservative for positional and split option values;
long-form `server_option` values remain available without a protocol opt-in.

Reuse the revision and pathspec option guards in `merge_base()` and `move()`,
with explicit `allow_unsafe_options` opt-ins. Git currently rejects these
denylisted options for those subcommands; the checks keep their policy aligned
with sibling APIs. Preserve literal move operands behind `--` and validate
options before either the dry run or actual move.

Only treat exit status 1 from `merge_base()` as no common ancestor. Other
failures, including invalid options, now propagate as `GitCommandError`
instead of silently returning an empty list.

Git reference: `git/git@d38352cd43ab9745686d697872408bc3249a153f`, inspected in
`builtin/ls-remote.c`, `transport.c`, `builtin/merge-base.c`, `builtin/mv.c`,
`url.c`, and `parse-options.c`. These confirm option parsing before the remote operand,
helper selection independently of address contents, long-option abbreviations,
and status 1 for unrelated histories.

Assisted-by: GPT 6.0
Co-authored-by: GPT 6.0 <codex@openai.com>