Mailglass.OptionalDeps (Mailglass v1.0.0)

Namespace for optional dependency gateway modules.

Each submodule gates one optional dependency behind a Code.ensure_loaded?/1 check and exposes available?/0. The @compile {:no_warn_undefined, ...} declaration in each gateway module (and the corresponding project-level elixirc_options list in mix.exs) suppresses compiler warnings when the dep is absent, so mix compile --no-optional-deps --warnings-as-errors stays green across the full matrix.

Pattern (CORE-06)

• Compile-time: @compile {:no_warn_undefined, [Module.Name, ...]} as the first declaration inside the gateway module, scoped to exactly the modules the gateway wraps.
• Runtime: available?/0 delegates to Code.ensure_loaded?/1 so callers can branch between the real dep and a degraded fallback without compiling against the optional dep.

Gateway Modules

• Mailglass.OptionalDeps.Oban — gates {:oban, "~> 2.21"}. Fallback for deliver_later/2 is Task.Supervisor (lands Phase 3).
• Mailglass.OptionalDeps.OpenTelemetry — gates {:opentelemetry, "~> 1.7"}. Adopter-owned bridge via opentelemetry_telemetry (D-32).
• Mailglass.OptionalDeps.Mjml — gates {:mjml, "~> 5.3"} (Rust NIF). Used by Mailglass.TemplateEngine.MJML when adopters opt into MJML (AUTHOR-05).
• Mailglass.OptionalDeps.GenSmtp — gates {:gen_smtp, "~> 1.3"}. Used by mailglass_inbound for SMTP relay ingress (v0.5+).
• Mailglass.OptionalDeps.Sigra — gates {:sigra, "~> 0.2"}. The module is conditionally compiled: it only exists when :sigra is loaded. Callers must guard via Code.ensure_loaded?(Mailglass.OptionalDeps.Sigra).

Lint Enforcement

Phase 6 ships a custom Credo check (NoBareOptionalDepReference) that flags any direct reference to the gated modules outside their corresponding gateway module. The gateway is the single authorized callsite.