PostgreSQL/pgvector implementation of Mnemosyne.GraphBackend.
Persists knowledge graph nodes in a single polymorphic nodes table
with JSONB data, vector embeddings, and JSONB link maps. Metadata
is stored in a separate node_metadata table.
Telemetry
See MnemosynePostgres.Telemetry for the full list of events and their
metadata.
Error handling
Callbacks whose behaviour spec includes {:error, ...} returns
(apply_changeset, delete_nodes, find_candidates, get_nodes_by_type)
catch exceptions and return {:error, StorageError.t()}. Callbacks that
only define {:ok, ...} returns (get_node, get_linked_nodes,
get_metadata, update_metadata, delete_metadata) let exceptions
propagate, as the caller is expected to handle crashes via supervision.