GenServer owning the :mailglass_fake_mailbox ETS table. Mirrors Swoosh.Adapters.Sandbox.Storage pattern: the GenServer handles ownership mutations (checkout, checkin, allow, set_shared, find_owner, {:DOWN, ...}) but READS happen directly against ETS to bypass the mailbox.

State

• :owners — MapSet of currently-checked-out owner pids.
• :allowed — map allowed_pid => owner_pid for allow-list delegation (LiveView, Playwright, Oban worker processes).
• :shared — single owner pid for global-mode tests (set via set_shared/1).
• :monitors — map monitor_ref => pid for auto-cleanup on DOWN.

ETS table

:mailglass_fake_mailbox — [:set, :named_table, :public, {:read_concurrency, true}]. Keys: owner pid. Values: list of records (prepended on each push, so newest is head).

Divergences from Swoosh.Adapters.Sandbox.Storage

1. Table name: :mailglass_fake_mailbox (not :swoosh_sandbox_emails).
2. Stored value: %{message: %Mailglass.Message{}, delivery_id: binary(), provider_message_id: binary(), recorded_at: DateTime.t()} — not a bare email.
3. send(owner_pid, {:mail, msg}) — not {:email, email}.
4. push/2 accepts owner_pid + record_map; stores full record in ETS.