Windows Sandbox - Alpha version (#4905)

- Added the new codex-windows-sandbox crate that builds both a library
entry point (run_windows_sandbox_capture) and a CLI executable to launch
commands inside a Windows restricted-token sandbox, including ACL
management, capability SID provisioning, network lockdown, and output
capture
(windows-sandbox-rs/src/lib.rs:167, windows-sandbox-rs/src/main.rs:54).
- Introduced the experimental WindowsSandbox feature flag and wiring so
Windows builds can opt into the sandbox:
SandboxType::WindowsRestrictedToken, the in-process execution path, and
platform sandbox selection now honor the flag (core/src/features.rs:47,
core/src/config.rs:1224, core/src/safety.rs:19,
core/src/sandboxing/mod.rs:69, core/src/exec.rs:79,
core/src/exec.rs:172).
- Updated workspace metadata to include the new crate and its
Windows-specific dependencies so the core crate can link against it
(codex-rs/
    Cargo.toml:91, core/Cargo.toml:86).
- Added a PowerShell bootstrap script that installs the Windows
toolchain, required CLI utilities, and builds the workspace to ease
development
    on the platform (scripts/setup-windows.ps1:1).
- Landed a Python smoke-test suite that exercises
read-only/workspace-write policies, ACL behavior, and network denial for
the Windows sandbox
    binary (windows-sandbox-rs/sandbox_smoketests.py:1).

codex-rs/core/src/config/mod.rs

@@ -769,6 +769,8 @@ impl ConfigToml {
         let mut forced_auto_mode_downgraded_on_windows = false;
         if cfg!(target_os = "windows")
             && matches!(resolved_sandbox_mode, SandboxMode::WorkspaceWrite)
+            // If the experimental Windows sandbox is enabled, do not force a downgrade.
+            && crate::safety::get_platform_sandbox().is_none()
         {
             sandbox_policy = SandboxPolicy::new_read_only_policy();
             forced_auto_mode_downgraded_on_windows = true;
@@ -900,6 +902,10 @@ impl Config {
         };
 
         let features = Features::from_config(&cfg, &config_profile, feature_overrides);
+        #[cfg(target_os = "windows")]
+        {
+            crate::safety::set_windows_sandbox_enabled(features.enabled(Feature::WindowsSandbox));
+        }
 
         let resolved_cwd = {
             use std::env;