release: package prebuilt resource binaries (#23759)

## Why

Release packaging should be a staging step once release binaries have
already been built and signed. The Windows release job was downloading
and signing `codex-command-runner.exe` and
`codex-windows-sandbox-setup.exe`, but `scripts/build_codex_package.py`
still rebuilt those helpers while creating the package archives.

That makes the package step slower and, more importantly, risks putting
helper binaries in the archive that were produced after the signing
step. Linux had the same shape for package resources: `bwrap` could be
rebuilt by the package builder instead of being passed in as a prebuilt
release artifact.

This builds on #23752, which fixes `.tar.zst` creation when Windows
runners rely on the repository DotSlash `zstd` wrapper.

## What changed

- Add explicit prebuilt resource inputs to the Codex package builder:
  - `--bwrap-bin`
  - `--codex-command-runner-bin`
  - `--codex-windows-sandbox-setup-bin`
- Make `.github/scripts/build-codex-package-archive.sh` pass resource
binaries from the release output directory when they are already
present.
- Build Linux `bwrap` for app-server release jobs too, so app-server
package creation does not invoke Cargo just to supply the package
resource.
- Keep macOS package creation as a no-Cargo path when `--entrypoint-bin`
is provided, since macOS packages have no resource binaries.
- Add unit coverage showing prebuilt macOS, Linux, and Windows package
inputs result in no source-built binaries.

## Verification

- `python3 -m unittest discover -s scripts/codex_package -p 'test_*.py'`
- `python3 -m py_compile scripts/codex_package/*.py`
- `bash -n .github/scripts/build-codex-package-archive.sh`
- Dry-ran Linux and Windows package builds with fake prebuilt resources
and a nonexistent Cargo path to verify the package builder did not
invoke Cargo.


---
[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/23759).
* #23760
* __->__ #23759

scripts/codex_package/cli.py

@@ -83,6 +83,32 @@ def parse_args() -> argparse.Namespace:
             "variant. If omitted, the entrypoint is built with Cargo."
         ),
     )
+    parser.add_argument(
+        "--bwrap-bin",
+        type=Path,
+        help=(
+            "Optional prebuilt Linux bwrap executable. If omitted for Linux "
+            "targets, bwrap is built with Cargo."
+        ),
+    )
+    parser.add_argument(
+        "--codex-command-runner-bin",
+        type=Path,
+        help=(
+            "Optional prebuilt Windows codex-command-runner.exe executable. "
+            "If omitted for Windows targets, codex-command-runner is built "
+            "with Cargo."
+        ),
+    )
+    parser.add_argument(
+        "--codex-windows-sandbox-setup-bin",
+        type=Path,
+        help=(
+            "Optional prebuilt Windows codex-windows-sandbox-setup.exe "
+            "executable. If omitted for Windows targets, "
+            "codex-windows-sandbox-setup is built with Cargo."
+        ),
+    )
     parser.add_argument(
         "--rg-bin",
         type=Path,
@@ -110,14 +136,25 @@ def main() -> int:
         variant,
         cargo=args.cargo,
         profile=args.cargo_profile,
-        entrypoint_bin=(
-            resolve_input_path(
-                args.entrypoint_bin,
-                "prebuilt entrypoint executable",
-                "--entrypoint-bin",
-            )
-            if args.entrypoint_bin is not None
-            else None
+        entrypoint_bin=resolve_optional_input_path(
+            args.entrypoint_bin,
+            "prebuilt entrypoint executable",
+            "--entrypoint-bin",
+        ),
+        bwrap_bin=resolve_optional_input_path(
+            args.bwrap_bin,
+            "prebuilt Linux bwrap executable",
+            "--bwrap-bin",
+        ),
+        codex_command_runner_bin=resolve_optional_input_path(
+            args.codex_command_runner_bin,
+            "prebuilt Windows codex-command-runner.exe executable",
+            "--codex-command-runner-bin",
+        ),
+        codex_windows_sandbox_setup_bin=resolve_optional_input_path(
+            args.codex_windows_sandbox_setup_bin,
+            "prebuilt Windows codex-windows-sandbox-setup.exe executable",
+            "--codex-windows-sandbox-setup-bin",
         ),
     )
     version = read_workspace_version()
@@ -139,3 +176,14 @@ def main() -> int:
 
     print(f"Built Codex package directory at {package_dir}")
     return 0
+
+
+def resolve_optional_input_path(
+    explicit_path: Path | None,
+    description: str,
+    flag_name: str,
+) -> Path | None:
+    if explicit_path is None:
+        return None
+
+    return resolve_input_path(explicit_path, description, flag_name)