Function wal_path_for 

pub fn wal_path_for(main: &Path) -> PathBuf

Construct the WAL sidecar path for a given main-file path. We append -wal to the file name (mirroring SQLite’s convention); the WAL lives next to the main file.

Exposed for integration tests and tooling that need to inspect or manipulate the sidecar directly (e.g. the crash-cycle fault harness and the eventual verifier CLI).