The boring ETS owner. Holds the snapshot table and does exactly two things: apply snapshots and settle the ready gate. All crash-prone work (HTTP, decode, backoff) lives in Lucerna.Gates.Sync — the supervisor's one_for_one strategy exists precisely so a Sync crash cannot take this table down with it.

Table layout (:protected, :named_table, read_concurrency):

• {{:kill, key}, boolean} / {{:flag, key}, map} / {{:experiment, key}, map} / {{:audience, id}, map} — one row per gate, so a read copies one gate's rules out of ETS, never the whole snapshot.
• {:document, map} — the last wire document, for evaluate, inspect_gate and runtime (cold paths).

• {:etag, binary | nil} — lives here, not in Sync, so a Store restart (fresh empty table) also resets the conditional-fetch state and the next poll refetches instead of trusting a 304.

• {:meta, map} — environment / generatedAt; presence means loaded.