Function launcher_saga_log_path_read_only 

pub fn launcher_saga_log_path_read_only(data_dir: &Path) -> PathBuf

Read-only resolver for the launcher saga log path. Returns whichever location actually holds the data: the canonical <data-dir>/db/launcher-sagas.db if present, otherwise the legacy <data-dir>/launcher-sagas.db if THAT exists, otherwise the canonical path (for the fresh-install case).

Does NOT touch the filesystem — safe for read-only callers like --diag sagas which document themselves as passive.