Embed the summary and upsert into the scope-specific collection.
Upsert is idempotent: re-indexing the same sessionId replaces
the prior vector rather than appending a duplicate.
Embed the query and return the top-K sessions for the given
scope, ordered by descending similarity. Returns [] when the
collection does not yet exist (cold scope).
Dedicated vector store wrapper for session-level summaries.
Example