Mediation Settings

ID: mediator.mediation-settings
Name: Mediation settings
Maturity: GA
Summary: Provides per-call routing, execution, and context item settings for command, query, and event mediation.

What It Does

Each semantic mediator accepts an optional settings object:

CommandMediationSettings
QueryMediationSettings
EventMediationSettings

Settings carry:

Routing (Tags, HandlerPredicate) for all message kinds.
Items dictionary for ambient execution context state.
Event-specific execution and no-handler behavior.

Public Surface

var settings = new EventMediationSettings
{
    ThrowIfNoHandlerFound = true,
    Routing = new EventRoutingSettings
    {
        Tags = ["Notifications"]
    },
    Execution = new EventExecutionSettings
    {
        PriorityGroupsConcurrencyMode = ConcurrencyMode.Sequential,
        HandlersWithinSamePriorityConcurrencyMode = ConcurrencyMode.Parallel,
        ParallelFaultMode = ParallelFaultMode.AggregateAll
    }
};

await eventMediator.PublishAsync(new OrderPlacedEvent(orderId), settings, cancellationToken);

API	Role
`CommandMediationSettings.Routing`	Command routing config
`CommandMediationSettings.Items`	Command ambient context seed
`QueryMediationSettings.Routing`	Query routing config
`QueryMediationSettings.Items`	Query ambient context seed
`EventMediationSettings.Routing`	Event routing config
`EventMediationSettings.Execution`	Event execution concurrency/fault mode
`EventMediationSettings.ThrowIfNoHandlerFound`	Event no-handler behavior
`EventMediationSettings.AutoRegisterUnregisteredMessageTypes`	On-the-spot registration for plain events

Packages

LiteBus.Commands.Abstractions
LiteBus.Queries.Abstractions
LiteBus.Events.Abstractions
LiteBus.Messaging.Abstractions

Requires

mediator.handler-filtering
mediator.execution-context
mediator.events (for execution settings)

Invariants

Default routing accepts all handlers (Tags empty and predicate returns true).
Items flow into AmbientExecutionContext.Current.Items for the mediation call.
ThrowIfNoHandlerFound only applies to event publish.
AutoRegisterUnregisteredMessageTypes only applies to event publish requests.

Non-Goals

Global default policy store across all mediator calls.
Persistence of settings beyond one mediator invocation.
Runtime mutation of module registration.

Observability

No settings-specific telemetry surfaces are emitted. Settings influence behavior but do not emit dedicated metrics.

Operational alternatives:

Log effective settings at call boundaries in application code.
Use test coverage to validate policy combinations for critical paths.

Test Coverage

Covered

Test method	Project
`mediating_event_with_no_handlers_should_throw_exception_when_ThrowIfNoHandlerFound_is_true`	`LiteBus.Mediator.UnitTests`
`mediating_event_with_no_handlers_should_not_throw_exception_when_ThrowIfNoHandlerFound_is_false`	`LiteBus.Mediator.UnitTests`
`mediating_event_with_items_in_settings_propagates_context_correctly`	`LiteBus.Mediator.UnitTests`
`mediating_an_command_with_specified_tag_goes_through_handlers_with_that_tag_and_handlers_without_any_tag_correctly`	`LiteBus.Mediator.UnitTests`
`Mediating_StreamQuery_PassesMetadataViaExecutionContext`	`LiteBus.Mediator.UnitTests`

Untested

Event AutoRegisterUnregisteredMessageTypes combined with large-scale polymorphic dispatch.
Cross-cutting settings policy helpers in external libraries.

Out-of-Scope

Long-lived session-level routing profiles.
Broker routing configuration.