host: expose harness state and actions over the world API

host/js/workspaces-test-bundle.js

@@ -30662,6 +30662,7 @@ async function loadExtensions(harness2, registry2, storage2, models2, context, b
       for (const { name, module } of modules) {
         const facet = scope(name, staged);
         next.push(facet);
+        facet.actions = Object.fromEntries((module.userActions ?? []).filter((key) => typeof module.actions?.[key] === "function").map((key) => [key, module.actions[key]]));
         facet.extension = typeof module.default === "function" ? await module.default(facet.host) : module.default;
         if (!facet.extension || facet.extension.name !== name) throw new Error(`Extension name must match ${name}`);
       }
@@ -30727,7 +30728,12 @@ Last good: ${fallback}` : failed;
       if (active) await enqueue2();
     }
   })();
-  return { reload: enqueue2, state: () => ({ ...state }), close: async () => {
+  return { reload: enqueue2, state: () => ({ ...state }), async invoke(name, key, args, signal, conversationId) {
+    const facet = facets.find((f) => f.extension.name === name);
+    const action = facet?.actions?.[key];
+    if (!action) throw Object.assign(new Error("Unknown user action"), { status: 404 });
+    return action(args, { host: facet.host, signal, conversationId, source: "ui" });
+  }, close: async () => {
     active = false;
     Deno.core.close(rid);
     await pending;