Function write_segment 

pub fn write_segment(
    dir: &Path,
    name: &str,
    dim: usize,
    vectors: &[&[f32]],
    surrogate_ids: &[u64],
) -> Result<()>

Write a v2 NDVS segment file as name inside dir.

surrogate_ids[i] is the u64 surrogate for vectors[i]. The slice may be empty, in which case all surrogate IDs are written as 0.

The segment is assembled in memory and published with a single write → sync_data → rename → fsync_dir sequence, so the final name only ever names a complete, footer-terminated segment. Writing into the final path directly had two crash windows: truncating it destroyed an existing segment before anything valid replaced it, and a crash between the body and footer syncs left a final-named file that no reader could validate.

Errors

Returns std::io::Error on any I/O failure, arithmetic overflow, or a name that is not one plain path component.