Receiving

Cratis.Showrunner.Marquee is the package a product references to show announcements. It also runs in the product’s own Arc and Chronicle process. It receives the contract events from the authoring store, records them once for the whole product, and answers, per tenant and per person, which announcements to show.

Add Marquee to a product

Reference the Cratis.Showrunner.Marquee package and call AddMarquee next to AddCratis:

var builder = WebApplication.CreateBuilder(args);
builder.AddCratis();
builder.AddMarquee(marquee =>
{
    marquee.Product = "ledger";
    marquee.AuthoringStores = ["Direct"];
});

Option	Default	Meaning
Product	none, required	The product this application is, as announcements name it. An authoring store serves several products; the product records only its own.
AuthoringStores	["Direct"]	The names of the event stores whose outbox the announcements come from, which is where authoring runs.
PollingInterval	one minute	How often Marquee makes sure the subscriptions exist and the inbox is observed.

The host fails to start when Product is not set. A module or plan audience is answered by the IAudienceEntitlements in the service collection; add Box Office’s before or after AddMarquee and it is used. Without one, only Everyone and Tenants audiences reach anybody; see Plugging in who holds a module.

The subscription

The contracts name no store, so nothing routes them on its own. For each authoring store, AddMarquee adds a hosted service that

• subscribes the product’s event store to the authoring store’s outbox, for the four announcement events, under the subscription id marquee-<store> (so it does not collide with a subscription another part such as Usher makes to the same store), and
• observes the inbox-<store> event sequence those events arrive in.

Both steps are idempotent and repeat every PollingInterval, so a restart or an authoring store that was not ready yet is caught up by the next round. The inbox reactor does not replay: replaying it would only receive again what is already recorded.

Recorded once, product-wide

An announcement is the same for every tenant, so it is recorded once, in the product’s own (default) namespace, and not copied to each tenant’s namespace. A tenant provisioned after an announcement was published still sees it while it is active.

MarqueeInbox turns each public event into a private fact and appends it under the announcement’s id, with event source type marquee:

Public event	Recorded as
AnnouncementPublished	AnnouncementReceived
AnnouncementRevised	AnnouncementRevisionReceived
AnnouncementAudienceChanged	AnnouncementAudienceChangeReceived
AnnouncementRetracted	AnnouncementRetractionReceived

A reducer folds them into StandingAnnouncement, one per announcement the product holds. A retraction removes it.

• Delivered at least once, recorded once. The fact is appended with an idempotency key derived from the event: the authoring store, the announcement, the event type, when it occurred, its correlation id and its content. Every copy of the same event yields one fact.
• Another product’s announcements are ignored. An event naming a product other than Product records nothing.

A retraction always wins

An announcement that was retracted is never brought back, whatever order its events arrive in. The inbox records a retraction even for an announcement it never received, and drops what arrives about the announcement after it: a publication, a revision or a new audience. It also drops a revision or a new audience for an announcement it never received, and a second publication of one it holds. All announcements of a product arrive under one event source, so the inbox handles them one at a time in the order they were published.

What a tenant sees

AnnouncementForMe.AnnouncementsForMe is an observable query that returns the announcements the signed-in person is to see in the current tenant. It resolves the tenant from Arc’s tenancy, keeps the standing announcements whose audience includes it, and leaves out a DialogOnce announcement the person already acknowledged. Nobody who is not signed in is authorized.

The query does not filter by date. An announcement scheduled for later is returned, with ActiveFrom and ActiveUntil, and the client compares the window with the clock every 60 seconds, so it appears on time without a round trip.