Reliable commits
Commit files are written atomically and include a CRC32 trailer. Recovery strips and validates the trailer before loading a commit. If the newest commit was torn or corrupted, LeanLucene falls back to an older valid generation.
IndexWriter runs recovery when it opens. SearcherManager also uses recovery
while polling, but without deleting orphaned files so readers stay safe.
Durable commits are on by default. Turn them off only for benchmarks where losing the latest commit is acceptable.