v7.0.0-preview.3

This is a pre-release of 7.0.0. Packages are published to NuGet with the 7.0.0-preview.3
version suffix, so dotnet add package only resolves them when a pre-release version is requested
explicitly or --prerelease is passed.

The notes below cover what changed since 7.0.0-preview.2. For everything landing in
7.0.0, see the 7.0.0 changelog.

What changed since v7.0.0-preview.2. This preview acts on the feedback from the first application to migrate onto
the v7 previews. Most of it is about the distance between what the pipeline could already express and what an
application still had to write by hand to use it: the audit trail knew what happened but not who did it, a refusal
could only be caught rather than received, a declaration had to be repeated on every message it applied to, and
nothing could report what the composition had actually assembled.

Added

• Actor attribution on the audit trail. AuditActor, IAuditActorResolver, and AuditRecord.Actor record who
  performed an audited action, which is the field an audit trail is least useful without.
• MessageModuleBuilder.AddAuditing configures the trail, the actor resolver, the outcome mapper, and which axes are
  audited in one place, in place of a sequence of separate registrations.
• Events are audited. An event now records alongside commands and queries instead of being excluded by construction.
• IMessageDefinition<TMessage>.Describe(IMessageDeclarations) declares several values for one message from a single
  definition class, rather than one class per declared value.
• Scoped declaration requirements. RequireDeclaration<TValue, TScope>() and the predicate overload require a value
  only of the messages a marker or a predicate covers, so one family can be held to a rule the rest is not.
• Family defaults. DeclareDefault<TScope, TValue>(value) and IMessageWriter.AddDeclaration(MessageDeclarationItem)
  declare a value once for a whole family; a message carrying its own still keeps it.
• Composition checks. ValidateComposition(Action<IMessageCatalog>), RequireUniqueAuditActions,
  RequireAuditActionFormat, and RequireExplicitOpenGenerics fail the build rather than a request in production.
• ICommandMediator.TrySendAsync, IQueryMediator.TryQueryAsync, and EvaluateAsync on both. A refusal arrives as a
  MediationResult instead of an exception, and EvaluateAsync asks whether a message would be permitted without
  performing it, which is what a UI needs to decide whether to offer the action at all.
• Mediation telemetry. An ActivitySource and a Meter named LiteBus.Mediation, MediationTelemetryOptions to
  choose what is emitted, and a new LiteBus.Messaging.Extensions.OpenTelemetry package registering both with a host.
• IMessageCatalog.Explain(Type) reports the pipeline a message will actually run as a MessagePipelinePlan, and
  LiteBusCompositionSummary reports what the composition assembled.
• MediationHarness in LiteBus.Testing.Mediation runs the shipped pipeline over hand-supplied handler instances, so
  a pipeline test does not need a container.
• The audit catalogue. AuditCatalogue.ToRows and ToMarkdown derive it from the declarations, and IMessageCatalog
  is registered as a Singleton so it resolves at runtime and not only inside a composition check.
• Keyed data on IExecutionContext.Data, a Code on Shortcut and on completion, and AuditReasonMissingException.
• Typed configuration exceptions: ModuleCompositionException, MessageDeclarationException,
  PipelineContractException, DurableStorageConfigurationException, and AuditConfigurationException.

Changed

• LiteBusConfigurationException is no longer sealed, because the typed exceptions above derive from it. A catch on
  the base still catches every one of them.
• The axis builders accept IMessageDefinition<> and the messaging-level handler contracts, so a definition or a guard
  written against the messaging abstractions registers on the axis whose message type it constrains.
• IExecutionContext is registered as Scoped, so a handler can take it as a dependency instead of reaching for the
  ambient accessor.

Fixed

• The events strategy dropped decision.Code, so an event denial reported no code.
• Describe is invoked reflectively, which wrapped a configuration error in TargetInvocationException.
• EventModule registered the audit completion handler after its handler scan, so the type never reached the container
  and no event was ever audited.
• [AuditExempt] accepted an empty rationale, which is the one thing the attribute exists to record.

Breaking

• HandlerPriorities.UnitOfWork moved to ReservedCeiling + 100. An application's unit-of-work commit now runs after
  the framework's own writers rather than between them, which is the order the inbox and the audit trail need to be
  committed in the same transaction as the work.
• ICommandMediator and IQueryMediator gained members without default implementations, so a hand-written
  implementation of either, such as a test double, has to implement them.

Documentation

• Arity-2 open generic handlers, IMessageShortcut<,> and IMessageRefusalMapper<,>, were already supported in
  preview.2 but undocumented. They are now recorded and covered by regression tests.
• The dispatch scope is created from the root scope factory, making it a sibling of the request scope rather than a
  child. hosted-services.md described a "per-request DbContext", which is the opposite of what happens.
• IExecutionContext.Data was missing from the execution context listings, and no page said what the Post stage is
  for.