VerticalSlices: Skill for Claude Code

Cross-Cutting Event Properties

Some information must travel with every event — correlation/causation ids, the authenticated actor, tenant context — but adding it as a property to every [EventType] would pollute the schemas. Chronicle solves this with ICanProvideAdditionalEventInformation (metadata-envelope providers) and event tags.

First, check the built-in EventContext

Before implementing a provider, see whether what you need is already there (available in reactors/reducers):

Property	Description
EventSourceId	the event source appended to
SequenceNumber	ordinal within the sequence
Occurred	wall-clock time at append
CorrelationId	propagated from the request (or generated)
Causation	upstream event references
CausedBy	actor identity (from the configured identity provider)

You don't need a custom provider for actor identity alone — CausedBy already captures it. Reach for a provider only for additional fields.

ICanProvideAdditionalEventInformation

using System.Text.Json.Nodes;

public class TenantMetadataProvider(IHttpContextAccessor http) : ICanProvideAdditionalEventInformation
{
    // ProvideFor receives the event as a JsonObject and mutates it in place; it returns Task.
    public Task ProvideFor(JsonObject @event)
    {
        @event["tenantId"] = http.HttpContext?.Request.Headers["x-tenant-id"].FirstOrDefault() ?? "Default";
        return Task.CompletedTask;
    }
}

Chronicle discovers providers from DI — register as scoped/singleton. Multiple providers merge; key collisions = last-registered wins. Place the class at a cross-cutting infrastructure location, not inside a slice. The properties land in the event's metadata envelope, not the event record — they are not surfaced in EventContext on reactive handlers. If a value must influence a projection/reducer, it belongs on the event type (or a dedicated audit event), not in cross-cutting metadata.