fix: wire plugin event subscriptions from worker to host

Plugin workers register event handlers via `ctx.events.on()` in the SDK,
but these subscriptions were never forwarded to the host process. The host
sends events via `notifyWorker("onEvent", ...)` which produces a JSON-RPC
notification (no `id`), but the worker only dispatched `onEvent` as a
request handler — notifications were silently dropped.

Changes:
- Add `events.subscribe` RPC method so workers can register subscriptions
  on the host-side event bus during setup
- Handle `onEvent` notifications in the worker notification dispatcher
  (previously only `agents.sessions.event` was handled)
- Add `events.subscribe` to HostServices interface, capability map, and
  host client handler
- Add `subscribe` handler in host services that registers on the scoped
  plugin event bus and forwards matched events to the worker

packages/plugins/sdk/src/host-client-factory.ts

@@ -103,9 +103,10 @@ export interface HostServices {
     list(params: WorkerToHostMethods["entities.list"][0]): Promise<WorkerToHostMethods["entities.list"][1]>;
   };
 
-  /** Provides `events.emit`. */
+  /** Provides `events.emit` and `events.subscribe`. */
   events: {
     emit(params: WorkerToHostMethods["events.emit"][0]): Promise<void>;
+    subscribe(params: WorkerToHostMethods["events.subscribe"][0]): Promise<void>;
   };
 
   /** Provides `http.fetch`. */
@@ -261,6 +262,7 @@ const METHOD_CAPABILITY_MAP: Record<WorkerToHostMethodName, PluginCapability | n
 
   // Events
   "events.emit": "events.emit",
+  "events.subscribe": "events.subscribe",
 
   // HTTP
   "http.fetch": "http.outbound",
@@ -407,6 +409,9 @@ export function createHostClientHandlers(
     "events.emit": gated("events.emit", async (params) => {
       return services.events.emit(params);
     }),
+    "events.subscribe": gated("events.subscribe", async (params) => {
+      return services.events.subscribe(params);
+    }),
 
     // HTTP
     "http.fetch": gated("http.fetch", async (params) => {

packages/plugins/sdk/src/protocol.ts

@@ -482,6 +482,10 @@ export interface WorkerToHostMethods {
     params: { name: string; companyId: string; payload: unknown },
     result: void,
   ];
+  "events.subscribe": [
+    params: { eventPattern: string; filter?: Record<string, unknown> | null },
+    result: void,
+  ];
 
   // HTTP
   "http.fetch": [

packages/plugins/sdk/src/worker-rpc-host.ts

@@ -387,6 +387,13 @@ export function startWorkerRpcHost(options: WorkerRpcHostOptions): WorkerRpcHost
             registration = { name, filter: filterOrFn, fn: maybeFn };
           }
           eventHandlers.push(registration);
+          // Register subscription on the host so events are forwarded to this worker
+          void callHost("events.subscribe", { eventPattern: name, filter: registration.filter ?? null }).catch((err) => {
+            notifyHost("log", {
+              level: "warn",
+              message: `Failed to subscribe to event "${name}" on host: ${err instanceof Error ? err.message : String(err)}`,
+            });
+          });
           return () => {
             const idx = eventHandlers.indexOf(registration);
             if (idx !== -1) eventHandlers.splice(idx, 1);
@@ -1107,6 +1114,14 @@ export function startWorkerRpcHost(options: WorkerRpcHostOptions): WorkerRpcHost
         const event = notif.params as AgentSessionEvent;
         const cb = sessionEventCallbacks.get(event.sessionId);
         if (cb) cb(event);
+      } else if (notif.method === "onEvent" && notif.params) {
+        // Plugin event bus notifications — dispatch to registered event handlers
+        handleOnEvent(notif.params as OnEventParams).catch((err) => {
+          notifyHost("log", {
+            level: "error",
+            message: `Failed to handle event notification: ${err instanceof Error ? err.message : String(err)}`,
+          });
+        });
       }
     }
   }

server/src/services/plugin-host-services.ts

@@ -556,6 +556,17 @@ export function buildHostServices(
         }
         await scopedBus.emit(params.name, params.companyId, params.payload);
       },
+      async subscribe(params: { eventPattern: string; filter?: Record<string, unknown> }) {
+        scopedBus.subscribe(
+          params.eventPattern as any,
+          params.filter as any ?? {},
+          async (event) => {
+            if (notifyWorker) {
+              notifyWorker("onEvent", { event });
+            }
+          },
+        );
+      },
     },
 
     http: {