package: include zsh fork in Codex package

Teach the Codex package builder to fetch the prebuilt zsh fork from a checked-in DotSlash manifest and install it under codex-resources/zsh/bin/zsh when an artifact is available for the package target.

Generalize the DotSlash download/cache/verify helper previously embedded in ripgrep packaging so additional checked-in DotSlash manifests can use the same SHA-256 and size validation path. Add install-context support for locating the bundled zsh fork and thread that path through config loading as the lowest-precedence zsh_path default, preserving explicit CLI/profile/global config values.

Also avoid preserving platform-specific file metadata when copying executables into the package directory so package smoke tests can use macOS system binaries as inputs.

scripts/codex_package/cli.py

@@ -15,6 +15,7 @@ from .targets import TARGET_SPECS
 from .targets import PackageInputs
 from .targets import default_target
 from .targets import resolve_input_path
+from .zsh import resolve_zsh_bin
 from .version import read_workspace_version
 
 
@@ -161,13 +162,14 @@ def main() -> int:
     inputs = PackageInputs(
         entrypoint_bin=source_outputs.entrypoint_bin,
         rg_bin=resolve_rg_bin(spec, args.rg_bin),
+        zsh_bin=resolve_zsh_bin(spec),
         bwrap_bin=source_outputs.bwrap_bin,
         codex_command_runner_bin=source_outputs.codex_command_runner_bin,
         codex_windows_sandbox_setup_bin=source_outputs.codex_windows_sandbox_setup_bin,
     )
     prepare_package_dir(package_dir, force=args.force)
     build_package_dir(package_dir, version, variant, spec, inputs)
-    validate_package_dir(package_dir, variant, spec)
+    validate_package_dir(package_dir, variant, spec, include_zsh=inputs.zsh_bin is not None)
 
     for archive_output in args.archive_output:
         archive_path = archive_output.resolve()