fix: prevent Computer Use subprocess leak on macOS

[guangsizhongbin]

Problem

Codex spawns a SkyComputerUseClient subprocess for each Computer Use session via the openai-bundled computer-use plugin, but does not reliably clean them up when conversations end. Over time these orphaned processes accumulate (~20MB RSS each), causing swap pressure and UI freezes.

On macOS, Codex++'s computer_use_guard was a no-op — all guard functionality was #[cfg(windows)] only.

Changes

computer_use_guard.rs

Added kill_orphaned_computer_use_processes() for macOS that uses pkill -f SkyComputerUseClient to clean up orphaned processes. Codex re-spawns them lazily on the next Computer Use session, so killing them is safe.

node_repl processes are intentionally left alone — they are lightweight (~1MB RSS) and killing them could disrupt in-flight code execution.

launcher.rs

Added a macOS-specific computer_use_guard_watchdog that runs every 120 seconds in a background tokio task. The watchdog is always active on macOS (not gated on computer_use_guard_enabled, which is a Windows-specific setting).

relay_config.rs

Replaced && let_chains syntax with nested if let blocks for broader Rust version compatibility. The let_chains feature requires nightly or specific Rust ≥1.86 nightly features.

Testing

• Compiles on Rust 1.87.0 (arm64 macOS)
• Binary runs as menu bar app
• Watchdog is registered via start_computer_use_guard_watchdog and runs every 2 minutes
• Cleanup successfully kills orphaned SkyComputerUseClient processes