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).

docs/sandbox.md

@@ -69,6 +69,12 @@ The mechanism Codex uses to enforce the sandbox policy depends on your OS:
 
 - **macOS 12+** uses **Apple Seatbelt**. Codex invokes `sandbox-exec` with a profile that corresponds to the selected `--sandbox` mode, constraining filesystem and network access at the OS level.
 - **Linux** combines **Landlock** and **seccomp** APIs to approximate the same guarantees. Kernel support is required; older kernels may not expose the necessary features.
+- **Windows (experimental)**:
+  - Launches commands inside a restricted token derived from an AppContainer profile.
+  - Grants only specifically requested filesystem capabilities by attaching capability SIDs to that profile.
+  - Disables outbound network access by overriding proxy-related environment variables and inserting stub executables for common network tools.
+
+Windows sandbox support remains highly experimental. It cannot prevent file writes, deletions, or creations in any directory where the Everyone SID already has write permissions (for example, world-writable folders).
 
 In containerized Linux environments (for example Docker), sandboxing may not work when the host or container configuration does not expose Landlock/seccomp. In those cases, configure the container to provide the isolation you need and run Codex with `--sandbox danger-full-access` (or the shorthand `--dangerously-bypass-approvals-and-sandbox`) inside that container.