24fe97a457
Replace LineIndex::from_reader(BufReader) with LineIndex::from_bytes(&mmap) in both open() and reload(), ensuring the line index is always built from the same mmap snapshot rather than a separate read through the file descriptor. This closes the race window where an external file modification between mmap() and from_reader() could cause line_index offsets to disagree with the mmap data, leading to get_line() returning wrong content or panicking. Closes #2