add dynamic worker create event (#3608)

src/backend/clients/event/types.ts

@@ -348,6 +348,18 @@ export type EventMap = {
     // is pricing workers that came into existence, not deploys.
     'worker.create': { actor: Actor; workerName: string };
 
+    // The same announcement for worker code that lives inside a hosted site
+    // and is deployed on demand rather than by an explicit call. Such a worker
+    // has no row of ours to key on, so what stands in for "genuinely new" is
+    // the absence of any prior record that it ran — which is why it is
+    // announced separately, and identified by where its source lives rather
+    // than by a worker name.
+    'worker.dynamic.create': {
+        actor: Actor;
+        subdomain: string;
+        worker: string;
+    };
+
     // ---- Outer / GUI broadcast ----
     'outer.cacheUpdate': {
         cacheKey: string[];