fix: address review feedback — subscription cleanup, filter nullability, stale diagram

- Add scopedBus.clear() in dispose() to prevent subscription accumulation
  on worker crash/restart cycles
- Use two-arg subscribe() overload when filter is null instead of passing
  empty object; fix filter type to include null
- Update ASCII flow diagram: onEvent is a notification, not request/response

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

@@ -19,8 +19,7 @@
  *   |--- request(initialize) ------------->  |  → calls plugin.setup(ctx)
  *   |<-- response(ok:true) ----------------  |
  *   |                                        |
- *   |--- request(onEvent) ---------------->  |  → dispatches to registered handler
- *   |<-- response(void) ------------------  |
+ *   |--- notification(onEvent) ----------->  |  → dispatches to registered handler
  *   |                                        |
  *   |<-- request(state.get) ---------------  |  ← SDK client call from plugin code
  *   |--- response(result) ---------------->  |

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

@@ -556,16 +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 });
-            }
-          },
-        );
+      async subscribe(params: { eventPattern: string; filter?: Record<string, unknown> | null }) {
+        const handler = async (event: import("@paperclipai/plugin-sdk").PluginEvent) => {
+          if (notifyWorker) {
+            notifyWorker("onEvent", { event });
+          }
+        };
+        if (params.filter) {
+          scopedBus.subscribe(params.eventPattern as any, params.filter as any, handler);
+        } else {
+          scopedBus.subscribe(params.eventPattern as any, handler);
+        }
       },
     },
 
@@ -1071,6 +1072,10 @@ export function buildHostServices(
     dispose() {
       disposed = true;
 
+      // Clear event bus subscriptions to prevent accumulation on worker restart.
+      // Without this, each crash/restart cycle adds duplicate subscriptions.
+      scopedBus.clear();
+
       // Snapshot to avoid iterator invalidation from concurrent sendMessage() calls
       const snapshot = Array.from(activeSubscriptions);
       activeSubscriptions.clear();