Releases resources the store owns.
Returns the number of stored rows.
Returns the active row for a symbol (case-insensitive), or null.
Creates the schema if needed. Idempotent and safe to call concurrently.
Returns the newest row timestamp, or null when the store is empty.
Atomically replaces the whole symbol set; rejects (leaving the old set intact) on failure.
Persistence backend for the symbol directory.