pub fn lean_ctx_data_dir() -> Result<PathBuf, String>Expand description
Resolve the lean-ctx data directory.
Priority order (backward-compatible XDG migration):
LEAN_CTX_DATA_DIRenv var (explicit override)~/.lean-ctxif it has actual data (stats.json/config.toml/sessions)$XDG_CONFIG_HOME/lean-ctx(XDG compliant, default~/.config/lean-ctx)
An empty ~/.lean-ctx/ directory does NOT trigger legacy mode — this prevents
data directory splits when setup creates the dir before MCP writes stats.