Function spawn_embed_backfill 

pub fn spawn_embed_backfill(
    memory: Arc<SemanticMemory>,
    timeout_secs: u64,
    progress_tx: Option<Sender<Option<BackfillProgress>>>,
) -> JoinHandle<()>

Spawn a background task that backfills missing embeddings.

Fire-and-forget: the caller does not need to await the returned handle. The task runs for at most timeout_secs seconds.

Errors

The returned JoinHandle resolves to () — errors are logged internally.