Libsql vectors

@mayurajs/vector-libsql implements the RAG contracts. Install it alongside mayura. Construction performs no I/O, credential discovery, provisioning or background work. All operations require an explicit host permission and a nonnegative costMicros ceiling. Offline tests and package checks passed locally. Real service behavior remains unqualified; see release validation status.

libsqlVectorStore accepts an explicit location: 'local' | 'hosted', dimensions, table, costMicros, permissions and a host-owned execute(sql, parameters, signal) callback returning row objects. Bind every parameter with the native driver; keep credentials and pooling in the host. The driver must cooperate with cancellation; an ignored abort can leave an uncertain write, which ingestion keeps quarantined. The adapter does not close the host driver.

Grant rag:transport:libsql for operations and rag:admin for explicit initialize(signal). Initialization creates only the named table. Provision the vector engine separately. Search uses exact cosine ordering with scope and metadata predicates inside SQL; it does not claim an approximate index or implicit lexical fallback. A production host can create a reviewed native index and tune its query plan separately.

Protocol reference, reviewed 2026-10-20: libsql documentation.