Caller-owned output slot populated by HnswIndex.saveTo once the
immutable generation is ready for meta-last publication. The receipt is a
cleanup candidate, not proof that publication committed: callers may pass
it to the internal stale-generation cleanup helper, which also compares the
live pointer's EmbedDb generation while holding the publisher lease.
Caller-owned output slot populated by HnswIndex.saveTo once the immutable generation is ready for meta-last publication. The receipt is a cleanup candidate, not proof that publication committed: callers may pass it to the internal stale-generation cleanup helper, which also compares the live pointer's EmbedDb generation while holding the publisher lease.