Check joined short-option values before Git execution

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GHSA-wvpp-8hx9-p66j reports that unsafe-option checks omitted the value
joined to a one-character option when split_single_char_options was false. A
regression test reproduced the mismatch: GitPython checked only -n even though
it emitted a joined -nVALUE token that Git parses as clustered short options.

Collect the exact joined token for unsplit one-character keyword arguments so
the existing clustered-short-option validation sees every option character.
The split form and long-option behavior remain unchanged.

A broader audit confirmed that all guarded keyword-forwarding APIs use
_option_candidates, including clone, ls-remote, fetch, pull, push, archive,
revision, diff, checkout-index, and tag paths. Git cf5497b14 confirms repeated
short-option parsing within a joined token. Focused candidate and unsafe-option
tests pass.

Assisted-by: GPT 5.6
Co-authored-by: GPT 5.6 <codex@openai.com>

git/cmd.py

@@ -1044,13 +1044,21 @@ def _option_candidates(cls, args: Sequence[Any] = (), kwargs: Optional[Mapping[s
                 values = value if isinstance(value, (list, tuple)) else (value,)
                 if any(value is True or (value is not False and value is not None) for value in values):
                     key = str(key)
-                    options.append(f"-{key}" if len(key) == 1 else f"--{dashify(key)}")
-                    if len(key) == 1 and split_single_char_options:
+                    if len(key) != 1:
+                        options.append(f"--{dashify(key)}")
+                    elif split_single_char_options:
+                        options.append(f"-{key}")
                         options.extend(
                             str(value)
                             for value in values
                             if value is not True and value not in (False, None) and str(value).startswith("-")
                         )
+                    else:
+                        options.extend(
+                            f"-{key}" if value is True else f"-{key}{value}"
+                            for value in values
+                            if value is True or (value is not False and value is not None)
+                        )
         return options
 
     AutoInterrupt: TypeAlias = _AutoInterrupt

test/test_git.py

@@ -230,7 +230,15 @@ def test_option_candidates_include_split_single_char_option_values(self):
 
         unsplit_kwargs = {"n": "--upload-pack=helper", "split_single_char_options": False}
         self.assertEqual(self.git.transform_kwargs(**unsplit_kwargs), ["-n--upload-pack=helper"])
-        self.assertEqual(Git._option_candidates(kwargs=unsplit_kwargs), ["-n"])
+        self.assertEqual(Git._option_candidates(kwargs=unsplit_kwargs), ["-n--upload-pack=helper"])
+
+    def test_option_candidates_include_joined_single_char_option_values(self):
+        kwargs = {"n": "uhelper", "split_single_char_options": False}
+        candidates = Git._option_candidates(kwargs=kwargs)
+
+        self.assertEqual(candidates, ["-nuhelper"])
+        with self.assertRaises(UnsafeOptionError):
+            Git.check_unsafe_options(options=candidates, unsafe_options=["-u"])
 
     _shell_cases = (
         # value_in_call, value_from_class, expected_popen_arg