Function storage_dir 

pub fn storage_dir(configured: Option<&Path>) -> PathBuf

Resolve the process-state storage root exactly once for every Rust entry point. The environment override is checked here so it wins over a stale plugin wire value, while both plugin-less fallback and plugin-injected paths share one root.

Last re-derived 2026-09-06 against subconscious d5e09914b0791a66f2a5a00a9bb3422860ade95e: compare the ordered variables, platform gates, and empty-value guards below with subc-core/src/daemon_config.rs::default_data_home, resolve its named constants, then preserve the documented Windows cache-class divergence.