[codex] Fix Windows BuildBuddy Bazel wrapper execution (#25915)

## Why

#25156 moved Bazel CI launches into a shared Python wrapper. On Windows,
launching Bazel with `os.execvp` can split the spaced
`--test_env=PATH=...` argument and fail to propagate the eventual Bazel
exit status, allowing jobs to pass without running tests. This reapplies
the wrapper after #25909 with a Windows-safe launch path.

## What changed

Use a waited `subprocess.run` launch on Windows while preserving
`os.execvp` on Unix. Add a process-level regression test for spaced
arguments and child exit status, and run it on Windows Bazel shard 1.

## Experiment

To confirm Bazel was actually invoking tests, patch `87b61d0be6`
temporarily added an intentionally failing `codex-core` unit test. Bazel
failed on that sentinel on all three major platforms:

- [Linux Bazel
test](https://github.com/openai/codex/actions/runs/26841132773/job/79151062486)
- [macOS Bazel
test](https://github.com/openai/codex/actions/runs/26841132773/job/79151062362)
- [Windows Bazel test shard
1/4](https://github.com/openai/codex/actions/runs/26841132773/job/79151062155)

The sentinel was removed after collecting this evidence. Windows Bazel
[clippy](https://github.com/openai/codex/actions/runs/26841132773/job/79151062914)
and [release
verification](https://github.com/openai/codex/actions/runs/26841132773/job/79151062739)
also passed.

## Validation

After removing the sentinel, `just test -p codex-core` no longer
reported it. The local run retained two unrelated environment-specific
failures.

.github/scripts/test_rusty_v8_bazel.py

@@ -88,24 +88,49 @@ class RustyV8BazelTest(unittest.TestCase):
             ),
         )
 
-    def test_bazel_remote_args_include_buildbuddy_header_when_present(self) -> None:
-        with patch.dict(environ, {"BUILDBUDDY_API_KEY": "token"}, clear=False):
+    def test_bazel_commands_use_shared_buildbuddy_remote_config_library(self) -> None:
+        with patch.dict(environ, {}, clear=True):
             self.assertEqual(
-                ["--remote_header=x-buildbuddy-api-key=token"],
-                rusty_v8_bazel.bazel_remote_args(),
+                [
+                    "bazel",
+                    "build",
+                    "//third_party/v8:release",
+                ],
+                rusty_v8_bazel.bazel_command(
+                    "build",
+                    "--config=ci-v8",
+                    "//third_party/v8:release",
+                ),
+            )
+        with patch.dict(environ, {"BUILDBUDDY_API_KEY": "token"}, clear=True):
+            self.assertEqual(
+                [
+                    "bazel",
+                    "build",
+                    "--config=buildbuddy-generic-rbe",
+                    "--remote_header=x-buildbuddy-api-key=token",
+                    "--config=ci-v8",
+                    "//third_party/v8:release",
+                ],
+                rusty_v8_bazel.bazel_command(
+                    "build",
+                    "--config=ci-v8",
+                    "//third_party/v8:release",
+                ),
             )
 
-        with patch.dict(environ, {}, clear=True):
-            self.assertEqual([], rusty_v8_bazel.bazel_remote_args())
-
-    def test_release_pair_labels_and_staged_names_distinguish_sandbox_artifacts(self) -> None:
+    def test_release_pair_labels_and_staged_names_distinguish_sandbox_artifacts(
+        self,
+    ) -> None:
         self.assertEqual(
             "//third_party/v8:rusty_v8_release_pair_x86_64_unknown_linux_musl",
             rusty_v8_bazel.release_pair_label("x86_64-unknown-linux-musl"),
         )
         self.assertEqual(
             "//third_party/v8:rusty_v8_sandbox_release_pair_x86_64_unknown_linux_musl",
-            rusty_v8_bazel.release_pair_label("x86_64-unknown-linux-musl", sandbox=True),
+            rusty_v8_bazel.release_pair_label(
+                "x86_64-unknown-linux-musl", sandbox=True
+            ),
         )
         self.assertEqual(
             "//third_party/v8:rusty_v8_sandbox_release_pair_x86_64_apple_darwin",
@@ -205,11 +230,7 @@ class RustyV8BazelTest(unittest.TestCase):
         with TemporaryDirectory() as source_dir, TemporaryDirectory() as output_dir:
             source_root = Path(source_dir)
             gn_out = (
-                source_root
-                / "target"
-                / "x86_64-pc-windows-msvc"
-                / "release"
-                / "gn_out"
+                source_root / "target" / "x86_64-pc-windows-msvc" / "release" / "gn_out"
             )
             (gn_out / "obj").mkdir(parents=True)
             (gn_out / "obj" / "rusty_v8.lib").write_bytes(b"archive")