windows-sandbox: add resolved permissions helper (#22896)

## Why

The Windows sandbox migration away from the legacy `SandboxPolicy`
abstraction needs a small local bridge before IPC and core wiring can
move to `PermissionProfile`. Leaf helpers currently branch directly on
`WorkspaceWrite`, which spreads legacy assumptions through path planning
and token setup code.

This PR introduces a Windows-local resolved permissions view so those
helpers can ask Windows-specific questions about runtime
filesystem/network permissions without matching on the legacy policy
enum everywhere.

## What changed

- Added `ResolvedWindowsSandboxPermissions` in
`windows-sandbox-rs/src/resolved_permissions.rs`, with legacy
`SandboxPolicy` constructors for the current call sites.
- Moved `allow.rs` writable-root and read-only-subpath planning onto the
resolved permissions type.
- Preserved Windows `TEMP`/`TMP` writable-root behavior when the
effective policy includes writable tmpdir access.
- Avoided resolving Unix `:slash_tmp` or parent-process `TMPDIR` while
computing Windows writable roots.
- Reused the shared allow-path result for setup write-root gathering and
routed network-block selection through the resolved abstraction.

## Verification

- `cargo test -p codex-windows-sandbox`
- `just fix -p codex-windows-sandbox`
- GitHub CI restarted on the amended commit; Windows Bazel is the
required signal for the Windows-only code paths.












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[//]: # (BEGIN SAPLING FOOTER)
Stack created with [Sapling](https://sapling-scm.com). Best reviewed
with [ReviewStack](https://reviewstack.dev/openai/codex/pull/22896).
* #23715
* #23714
* #23167
* #22923
* #22918
* __->__ #22896

codex-rs/windows-sandbox-rs/src/spawn_prep.rs

@@ -19,6 +19,7 @@ use crate::logging::log_start;
 use crate::path_normalization::canonicalize_path;
 use crate::policy::SandboxPolicy;
 use crate::policy::parse_policy;
+use crate::resolved_permissions::ResolvedWindowsSandboxPermissions;
 use crate::sandbox_utils::ensure_codex_home_exists;
 use crate::sandbox_utils::inject_git_safe_directory;
 use crate::setup::effective_write_roots_for_setup;
@@ -73,7 +74,7 @@ pub(crate) struct LegacyAclSids<'a> {
 }
 
 pub(crate) fn should_apply_network_block(policy: &SandboxPolicy) -> bool {
-    !policy.has_full_network_access()
+    ResolvedWindowsSandboxPermissions::from_legacy_policy(policy).should_apply_network_block()
 }
 
 fn prepare_spawn_context_common(