XPC executor for faster IPC

[frouaix]

Summary

Replace the current CLI-based IPC (JSON over stdin/stdout with child process spawning) with XPC for faster, more efficient communication.

Details

• Currently, the TypeScript MCP server spawns the Swift executor as a child process and communicates via JSON over stdin/stdout
• XPC would provide:
  • Lower latency (no process spawn per call)
  • Better resource management
  • Native macOS IPC with Mach messaging
• Requires an XPC service target in the Swift package
• The TypeScript side would need an XPC client (likely via a native addon or a long-lived bridge process)
• This is a significant architectural change

Affected components

• packages/executor-swift/ — convert to XPC service
• packages/mcp-server/src/exec/ — replace child process spawning with XPC client

Phase 23 item

From TODO.md

Phase 23: XPC executor — Replace CLI-based IPC with XPC for faster communication