Core: Prevent story-local viewport from persisting in URL

code/core/src/manager-api/modules/globals.ts

@@ -130,22 +130,20 @@ export const init: ModuleFn<SubAPI, SubState> = ({ store, fullAPI, provider }) =
     SET_GLOBALS,
     function handleSetGlobals(this: any, { globals, globalTypes }: SetGlobalsPayload) {
       const { ref } = getEventMetadata(this, fullAPI)!;
-      const currentGlobals = store.getState()?.globals;
+      const currentUserGlobals = store.getState()?.userGlobals;
 
       if (!ref) {
         store.setState({ globals, userGlobals: globals, globalTypes });
       } else if (Object.keys(globals).length > 0) {
         logger.warn('received globals from a non-local ref. This is not currently supported.');
       }
 
-      // If we have stored globals different to what the preview just inited with,
-      // we should update it to those values
       if (
-        currentGlobals &&
-        Object.keys(currentGlobals).length !== 0 &&
-        !deepEqual(globals, currentGlobals)
+        currentUserGlobals &&
+        Object.keys(currentUserGlobals).length !== 0 &&
+        !deepEqual(globals, currentUserGlobals)
       ) {
-        api.updateGlobals(currentGlobals);
+        api.updateGlobals(currentUserGlobals);
       }
     }
   );

code/core/src/manager-api/tests/globals.test.ts

@@ -71,7 +71,7 @@ describe('globals API', () => {
     });
   });
 
-  it('emits UPDATE_GLOBALS if retains a globals value different to what receives on SET_GLOBALS', () => {
+  it('emits UPDATE_GLOBALS if retains a user globals value different to what receives on SET_GLOBALS', () => {
     const channel = new EventEmitter();
     const listener = vi.fn();
     channel.on(UPDATE_GLOBALS, listener);
@@ -83,6 +83,7 @@ describe('globals API', () => {
     } as unknown as ModuleArgs);
     store.setState({
       ...state,
+      userGlobals: { a: 'c' },
       globals: { a: 'c' },
     });
 
@@ -103,6 +104,31 @@ describe('globals API', () => {
     });
   });
 
+  it('does not push story globals to preview when SET_GLOBALS fires with empty globals', () => {
+    const channel = new EventEmitter();
+    const listener = vi.fn();
+    channel.on(UPDATE_GLOBALS, listener);
+
+    const store = createMockStore();
+    const { state } = initModule({
+      store,
+      provider: { channel },
+    } as unknown as ModuleArgs);
+    store.setState({
+      ...state,
+      userGlobals: {},
+      storyGlobals: { viewport: 'mobile1' },
+      globals: { viewport: 'mobile1' },
+    });
+
+    channel.emit(SET_GLOBALS, {
+      globals: {},
+      globalTypes: {},
+    } satisfies SetGlobalsPayload);
+
+    expect(listener).not.toHaveBeenCalled();
+  });
+
   it('ignores SET_STORIES from other refs', () => {
     const channel = new EventEmitter();
     const api = { findRef: vi.fn() };