Lightweight PubSub broadcast transport for real-time events.

Broadcasts event payload directly to a Phoenix channel without creating Notification records. Uses the same pubsub_module and channel_topic config as other transports — everything config-derived.

Receipt is created (audit trail) and immediately marked as sent.

Features

• invalidates — event-declared frontend cache keys included in payload
• throttle_ms — per-user+event rate limiting via ETS (metadata option)

Channel Config

[transport: :broadcast, audience: :user]
[transport: :broadcast, audience: :admin]

Admin audience broadcasts to the firehose topic configured via :admin_channel_topic (default: "admin:firehose").