fix: allow file-map-executable for vllm-metal cache in macOS sandbox

The pre-compiled paged_ops .so extension needs to be dlopen()'d at
runtime, which requires mmap with execute permissions. Add a targeted
file-map-executable allowance for ~/.cache/vllm-metal where the
pre-built extension is cached.

Author: ilopezluna

pkg/sandbox/sandbox_darwin.go

@@ -88,6 +88,9 @@ const ConfigurationPython = `(version 1)
     (subpath "[HOMEDIR]/.cache/vllm")
     (subpath "[HOMEDIR]/.cache/vllm-metal")
     (subpath "/private/tmp"))
+;;; Allow loading pre-compiled Metal kernel extensions from the vllm-metal cache.
+(allow file-map-executable
+    (subpath "[HOMEDIR]/.cache/vllm-metal"))
 `
 
 // ConfigurationLlamaCpp is the sandbox configuration for llama.cpp processes.