Function resolve_global_shared_root 

pub(crate) fn resolve_global_shared_root() -> Option<PathBuf>

The global, channel-independent <home>/shared root. Deliberately UNAFFECTED by isolated_auth_enabled() — callers that need the true ~/.agentmux home (e.g. migrations/runner.rs’s MigrationContext.home) must call this directly rather than deriving it from resolve_shared_store_path(), which DOES vary with isolation.