pub fn data_dir() -> Result<PathBuf>Expand description
Per-platform data dir for durable state: $XDG_DATA_HOME/mcpmesh when that
var is set, non-empty, and absolute; otherwise $HOME/.local/share/mcpmesh (unix).
state.redb (the peer allowlist) lives here. Unlike the runtime dir (ephemeral, per-boot),
this is durable across reboots. On Windows, %LOCALAPPDATA%\mcpmesh\data (LOCALAPPDATA,
not APPDATA — this data need not roam with the user profile).