Event Backend Architecture

The event system lives in victor.core.events. Use the event-bus guide
for the current publishing and subscription interfaces, and the
observability overview for metrics and telemetry.

ObservabilityBus carries telemetry; AgentMessageBus carries agent messages.
create_event_backend() selects a registered implementation. Its default is in-memory;
an unregistered backend falls back to in-memory with a warning. Register and configure a
backend before relying on persistence or cross-process delivery.

The configuration setting is event_backend_type (VICTOR_EVENT_BACKEND_TYPE), not the
removed eventbus_backend / VICTOR_EVENTBUS_BACKEND. JSONL metrics export is a separate
consumer, not a guarantee of distributed message delivery.

The previous factory guide described removed victor.observability.event_bus_factory
and victor.observability.event_bus modules. Its migration examples and old dashboard
recipes remain available in git history.

Source: victor/core/events/__init__.py, victor/core/events/backends.py, and
victor/config/settings.py.