linux-sandbox: switch helper plumbing to PermissionProfile (#20106)

## Why

`PermissionProfile` is the canonical runtime permission model in the
Rust workspace, but the Linux sandbox helper still accepted a legacy
`SandboxPolicy` plus separate filesystem and network policy flags. That
translation layer made the helper interface harder to reason about and
left `linux-sandbox`-specific callers and tests coupled to the legacy
policy representation.

This change moves the helper onto `PermissionProfile` directly so the
Linux sandbox plumbing matches the rest of the permission stack.

## What changed

- changed `codex-linux-sandbox` to accept `--permission-profile` and
derive the runtime filesystem and network policies internally
- updated the in-process seccomp and legacy Landlock path in
`codex-rs/linux-sandbox` to operate on `PermissionProfile`
- updated Linux sandbox argv construction in `codex-rs/sandboxing`,
`codex-rs/core`, and the CLI debug sandbox path to pass the canonical
profile instead of serializing compatibility policy projections
- simplified the Linux sandbox tests to build the exact permission
profile under test, including the managed-proxy path and
direct-runtime-enforcement carveout coverage
- removed helper-local `SandboxPolicy` usage from `bwrap` tests where
`FileSystemSandboxPolicy` is already the value being exercised

## Testing

- `cargo test -p codex-sandboxing`
- `cargo test -p codex-linux-sandbox` (on this macOS host, the crate
compiled cleanly and its Linux-only tests were cfg-gated)
- `cargo test -p codex-core --no-run`
- `cargo test -p codex-cli --no-run`

codex-rs/cli/src/debug_sandbox.rs

@@ -16,7 +16,8 @@ use codex_core::spawn::CODEX_SANDBOX_ENV_VAR;
 use codex_core::spawn::CODEX_SANDBOX_NETWORK_DISABLED_ENV_VAR;
 use codex_protocol::config_types::SandboxMode;
 use codex_protocol::permissions::NetworkSandboxPolicy;
-use codex_sandboxing::landlock::create_linux_sandbox_command_args_for_policies;
+use codex_sandboxing::landlock::allow_network_for_proxy;
+use codex_sandboxing::landlock::create_linux_sandbox_command_args_for_permission_profile;
 #[cfg(target_os = "macos")]
 use codex_sandboxing::seatbelt::CreateSeatbeltCommandArgsParams;
 #[cfg(target_os = "macos")]
@@ -222,19 +223,14 @@ async fn run_command_under_sandbox(
                 .codex_linux_sandbox_exe
                 .expect("codex-linux-sandbox executable not found");
             let use_legacy_landlock = config.features.use_legacy_landlock();
-            let file_system_sandbox_policy = config.permissions.file_system_sandbox_policy();
             let network_sandbox_policy = config.permissions.network_sandbox_policy();
-            let args = create_linux_sandbox_command_args_for_policies(
+            let args = create_linux_sandbox_command_args_for_permission_profile(
                 command,
                 cwd.as_path(),
-                &config
-                    .permissions
-                    .legacy_sandbox_policy(sandbox_policy_cwd.as_path()),
-                &file_system_sandbox_policy,
-                network_sandbox_policy,
+                &config.permissions.permission_profile(),
                 sandbox_policy_cwd.as_path(),
                 use_legacy_landlock,
-                /*allow_network_for_proxy*/ false,
+                allow_network_for_proxy(managed_network_requirements_enabled),
             );
             spawn_debug_sandbox_child(
                 codex_linux_sandbox_exe,