Function export_subset 

pub fn export_subset(
    out_dir: &Path,
    ids: &[String],
) -> Result<Vec<(String, u64)>>

Re-export the subset of stories identified by ids. Empty ids means “re-export everything plus the index”. The shared style.css is rewritten on every call so a CSS edit picked up by the worker still propagates.

Returns a vector of (id, elapsed_ms) tuples for everything rendered, in the order rendered.

Errors

Returns an io::Error if any file write fails or a story id is unknown to the registry.