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/cargo.py

@@ -28,11 +28,25 @@ def build_source_binaries(
     cargo: str,
     profile: str,
     entrypoint_bin: Path | None,
+    bwrap_bin: Path | None,
+    codex_command_runner_bin: Path | None,
+    codex_windows_sandbox_setup_bin: Path | None,
 ) -> SourceBuildOutputs:
+    validate_prebuilt_resource_inputs(
+        spec,
+        bwrap_bin=bwrap_bin,
+        codex_command_runner_bin=codex_command_runner_bin,
+        codex_windows_sandbox_setup_bin=codex_windows_sandbox_setup_bin,
+    )
     binaries = source_binaries_for_target(
         spec,
         variant,
         build_entrypoint=entrypoint_bin is None,
+        build_bwrap=spec.is_linux and bwrap_bin is None,
+        build_codex_command_runner=spec.is_windows
+        and codex_command_runner_bin is None,
+        build_codex_windows_sandbox_setup=spec.is_windows
+        and codex_windows_sandbox_setup_bin is None,
     )
     if binaries:
         cmd = [
@@ -51,17 +65,21 @@ def build_source_binaries(
 
     output_dir = cargo_profile_output_dir(spec, profile)
     outputs = SourceBuildOutputs(
-        entrypoint_bin=(
-            entrypoint_bin.resolve()
-            if entrypoint_bin is not None
-            else output_dir / variant.entrypoint_name(spec)
+        entrypoint_bin=resolve_output_path(
+            entrypoint_bin,
+            output_dir / variant.entrypoint_name(spec),
         ),
-        bwrap_bin=output_dir / "bwrap" if spec.is_linux else None,
-        codex_command_runner_bin=(
-            output_dir / "codex-command-runner.exe" if spec.is_windows else None
+        bwrap_bin=resolve_output_path(
+            bwrap_bin,
+            output_dir / "bwrap" if spec.is_linux else None,
         ),
-        codex_windows_sandbox_setup_bin=(
-            output_dir / "codex-windows-sandbox-setup.exe" if spec.is_windows else None
+        codex_command_runner_bin=resolve_output_path(
+            codex_command_runner_bin,
+            output_dir / "codex-command-runner.exe" if spec.is_windows else None,
+        ),
+        codex_windows_sandbox_setup_bin=resolve_output_path(
+            codex_windows_sandbox_setup_bin,
+            output_dir / "codex-windows-sandbox-setup.exe" if spec.is_windows else None,
         ),
     )
     validate_source_outputs(outputs)
@@ -73,22 +91,48 @@ def source_binaries_for_target(
     variant: PackageVariant,
     *,
     build_entrypoint: bool,
+    build_bwrap: bool,
+    build_codex_command_runner: bool,
+    build_codex_windows_sandbox_setup: bool,
 ) -> list[str]:
     binaries = []
     if build_entrypoint:
         binaries.append(variant.cargo_bin)
-    if spec.is_linux:
+    if build_bwrap:
         binaries.append("bwrap")
-    if spec.is_windows:
-        binaries.extend(
-            [
-                "codex-command-runner",
-                "codex-windows-sandbox-setup",
-            ]
-        )
+    if build_codex_command_runner:
+        binaries.append("codex-command-runner")
+    if build_codex_windows_sandbox_setup:
+        binaries.append("codex-windows-sandbox-setup")
     return binaries
 
 
+def validate_prebuilt_resource_inputs(
+    spec: TargetSpec,
+    *,
+    bwrap_bin: Path | None,
+    codex_command_runner_bin: Path | None,
+    codex_windows_sandbox_setup_bin: Path | None,
+) -> None:
+    if bwrap_bin is not None and not spec.is_linux:
+        raise RuntimeError("--bwrap-bin is only supported for Linux targets.")
+    if codex_command_runner_bin is not None and not spec.is_windows:
+        raise RuntimeError(
+            "--codex-command-runner-bin is only supported for Windows targets."
+        )
+    if codex_windows_sandbox_setup_bin is not None and not spec.is_windows:
+        raise RuntimeError(
+            "--codex-windows-sandbox-setup-bin is only supported for Windows targets."
+        )
+
+
+def resolve_output_path(explicit_path: Path | None, default_path: Path | None) -> Path | None:
+    if explicit_path is not None:
+        return explicit_path.resolve()
+
+    return default_path
+
+
 def cargo_profile_output_dir(spec: TargetSpec, profile: str) -> Path:
     target_dir = cargo_target_dir()
     return target_dir / spec.target / cargo_profile_dirname(profile)