Default cross-session memory provider: a self-contained ETS+DETS store.

Follows the Raxol.Payments.Mandate.Store pattern: a GenServer owns writes, reads bypass through ETS directly (read_concurrency: true). Table names are derived from the registered name, so multiple instances can coexist via a distinct :name.

Tables (derived from the server name)

• primary :set {id, record}
• Tok :bag {token, id} - inverted index
• Tag :bag {tag, id}
• Agent :bag {agent_id, id} - per-agent partition
• DF :set {token, doc_freq} plus {:__N__, doc_count} and {:__DL__, total_doc_len} for IDF / average document length

Only the primary records are persisted to DETS (:dets_path opt or the :memory_store_path Application key); every secondary index, including DF, is rebuilt from the primary records on open, so no stale index can survive a restart.

Ranking (pure Elixir, no SQLite/NIF)

score = relevance + recency + tag_bonus, where relevance is a length- normalized BM25-lite sum of IDF over matching query tokens, recency decays exponentially from last_accessed, and tag_bonus rewards tag overlap. An empty query degrades to recency-only most-recent-N (the prefetch default).