Gateway for the optional Oban dependency ({:oban, "~> 2.21"}).

When Oban is present, available?/0 returns true and callers may safely reference Oban, Oban.Worker, and Oban.Job. When absent, Mailglass.Outbound.deliver_later/2 falls back to Task.Supervisor with a Logger.warning emitted at boot (see Mailglass.Application).

Oban integration lands in Phase 3 (Outbound). This gateway is delivered in Phase 1 so Config/Telemetry can reference it without forward-reference pain.

Phase 2 addition — TenancyMiddleware (D-33)

Mailglass.Oban.TenancyMiddleware (defined as a sibling module in this file, conditionally compiled when Oban.Worker is loaded) serializes Mailglass.Tenancy.current/0 into job args on enqueue and restores it via put_current/1 in perform/1. Mitigates process-dict-leakage risk across background boundaries. The module is absent when Oban is not loaded — mix compile --no-optional-deps --warnings-as-errors passes cleanly.

OSS Oban 2.21 has no first-class middleware behaviour (that lives in Oban Pro). Mailglass ships the middleware as a plain module exposing call/2 (the shape an adopter using Oban Pro can register directly) PLUS a wrap_perform/2 helper that adopters using OSS Oban invoke inside their worker's perform/1. Both paths converge on the same Mailglass.Tenancy.with_tenant/2 wrap.

Lint Enforcement (Phase 6)

The Credo check NoBareOptionalDepReference flags direct Oban.* calls outside this module. All Oban interaction routes through the Outbound facade, which consults available?/0 before dispatching.