sing-box: Don'have permission to create cache file

Package Name

sing-box

Maintainer

@brvphoenix

OpenWrt Version

25.12.2

OpenWrt Target/Subtarget

ramips/mt7621

Steps to Reproduce

1. compile 25.12 with the package and have a fresh installation
2. add cachefile settings to config.json like:

{
  ...
  "experimental": {
    "cache_file": {"enabled": true,"path": "/etc/sing-box/cache.db","store_fakeip": true},
    "clash_api": {"external_ui": "ui","external_controller": "0.0.0.0:7890","external_ui_download_url": "https://gh-proxy.com/https://github.com/MetaCubeX/metacubexd/archive/refs/heads/gh-pages.zip","external_ui_download_detour": "direct"}
  }
  ...
}

3. start sing-box service and get error log daemon.err: sing-box[8917]: [31mFATAL[0m[0001] start service: initialize cache-file: open /etc/sing-box/cache.db: permission denied

Actual Behaviour

In a typical sing-box configuration, the cache file /etc/sing-box/cache.db is used to store webUI settings, DNS cache or fake IP addresses. When I compile 25.12 with the package and have a fresh installation on router, this file fails to create, resulting in a service starting failure.

Confirmation Checklist

• The package is maintained in this repository.
• I understand that issues related to the base OpenWrt repository or LuCI repository will be closed.
• I am reporting an issue for OpenWrt, not an unsupported fork.

Start by inspecting the sing-box package definition and its service configuration, then reproduce the fresh-install setup with the shown cache_file path. Trace which account starts the service and whether it can create /etc/sing-box/cache.db; done means the package permits the configured cache file and sing-box starts successfully on the listed OpenWrt target.