Fix sandbox extraction follow-ups

- trim leftover codex-core sandbox shims and retarget the remaining type plumbing
- keep sandbox-related dependencies scoped to the crates and targets that actually use them

Co-authored-by: Codex <noreply@openai.com>

codex-rs/core/src/error.rs

@@ -15,6 +15,7 @@ use codex_protocol::ThreadId;
 use codex_protocol::protocol::CodexErrorInfo;
 use codex_protocol::protocol::ErrorEvent;
 use codex_protocol::protocol::RateLimitSnapshot;
+use codex_sandbox::SandboxTransformError;
 use reqwest::StatusCode;
 use serde_json;
 use std::io;
@@ -234,6 +235,20 @@ impl From<codex_sandbox::error::CodexErr> for CodexErr {
     }
 }
 
+impl From<SandboxTransformError> for CodexErr {
+    fn from(err: SandboxTransformError) -> Self {
+        match err {
+            SandboxTransformError::MissingLinuxSandboxExecutable => {
+                CodexErr::LandlockSandboxExecutableNotProvided
+            }
+            #[cfg(not(target_os = "macos"))]
+            SandboxTransformError::SeatbeltUnavailable => CodexErr::UnsupportedOperation(
+                "seatbelt sandbox is only available on macOS".to_string(),
+            ),
+        }
+    }
+}
+
 impl CodexErr {
     pub fn is_retryable(&self) -> bool {
         match self {