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/sandboxing/src/manager.rs

@@ -4,7 +4,7 @@ use crate::bwrap::WSL1_BWRAP_WARNING;
 use crate::bwrap::is_wsl1;
 use crate::landlock::CODEX_LINUX_SANDBOX_ARG0;
 use crate::landlock::allow_network_for_proxy;
-use crate::landlock::create_linux_sandbox_command_args_for_policies;
+use crate::landlock::create_linux_sandbox_command_args_for_permission_profile;
 use crate::policy_transforms::effective_permission_profile;
 use crate::policy_transforms::should_require_platform_sandbox;
 use codex_network_proxy::NetworkProxy;
@@ -186,12 +186,6 @@ impl SandboxManager {
             effective_permission_profile(permissions, additional_permissions.as_ref());
         let (effective_file_system_policy, effective_network_policy) =
             effective_permission_profile.to_runtime_permissions();
-        let effective_policy = compatibility_sandbox_policy_for_permission_profile(
-            &effective_permission_profile,
-            &effective_file_system_policy,
-            effective_network_policy,
-            sandbox_policy_cwd,
-        );
         let mut argv = Vec::with_capacity(1 + command.args.len());
         argv.push(command.program);
         argv.extend(command.args.into_iter().map(OsString::from));
@@ -231,12 +225,10 @@ impl SandboxManager {
                     allow_proxy_network,
                     is_wsl1(),
                 )?;
-                let mut args = create_linux_sandbox_command_args_for_policies(
+                let mut args = create_linux_sandbox_command_args_for_permission_profile(
                     os_argv_to_strings(argv),
                     command.cwd.as_path(),
-                    &effective_policy,
-                    &effective_file_system_policy,
-                    effective_network_policy,
+                    &effective_permission_profile,
                     sandbox_policy_cwd,
                     use_legacy_landlock,
                     allow_proxy_network,