Fix source selection after disabling dual output

app/components-react/editor/elements/SourceSelector.tsx

@@ -387,6 +387,7 @@ class SourceSelectorController {
        * clicking on the source selector selects both sources
        */
       if (
+        this.isDualOutputActive &&
         this.dualOutputService.views.hasNodeMap(this.scene.id) &&
         this.dualOutputService.views.activeDisplays.horizontal &&
         this.dualOutputService.views.activeDisplays.vertical
@@ -504,6 +505,7 @@ class SourceSelectorController {
      * in the vertical display, convert the vertical node id to the horizontal node id.
      */
     if (
+      this.isDualOutputActive &&
       this.dualOutputService.views.activeDisplays.horizontal &&
       this.dualOutputService.views.activeDisplays.vertical
     ) {

app/services/dual-output/dual-output.ts

@@ -174,7 +174,7 @@ class DualOutputViews extends ViewHandler<IDualOutputServiceState> {
   }
 
   get onlyVerticalDisplayActive() {
-    return this.activeDisplays.vertical && !this.activeDisplays.horizontal;
+    return this.dualOutputMode && this.activeDisplays.vertical && !this.activeDisplays.horizontal;
   }
 
   get platformsDualStreaming() {

app/services/scenes/scene.ts

@@ -151,9 +151,7 @@ export class Scene {
   getSourceSelectorNodes(): TSceneNode[] {
     let nodes = this.getNodes();
 
-    const populateWithVerticalNodes =
-      !this.dualOutputService.views.activeDisplays.horizontal &&
-      this.dualOutputService.views.activeDisplays.vertical;
+    const populateWithVerticalNodes = this.dualOutputService.views.onlyVerticalDisplayActive;
 
     nodes = nodes.filter(node => {
       // if only the vertical display is active

test/regular/api/dual-output.ts

@@ -3,11 +3,87 @@ import { getApiClient } from '../../helpers/api-client';
 import { test, useWebdriver, TExecutionContext } from '../../helpers/webdriver';
 import { ScenesService, Scene, SceneItem } from 'services/scenes';
 import { VideoSettingsService } from 'services/settings-v2/video';
+import { SelectionService } from 'services/api/external-api/selection';
+import { click, focusMain, waitForDisplayed } from '../../helpers/modules/core';
 
 // not a react hook
 // eslint-disable-next-line react-hooks/rules-of-hooks
 useWebdriver();
 
+testSelectionAfterDisablingDualOutput(false);
+testSelectionAfterDisablingDualOutput(true);
+
+async function setDualOutputMode(status: boolean) {
+  const client = await getApiClient();
+  // The RPC fallback exposes this private method; its loading-mode decorator returns a promise.
+  const dualOutput = client.getResource<{
+    setDualOutputMode(status: boolean, skipShowVideoSettings: boolean): Promise<void>;
+  }>('DualOutputService');
+
+  // Exercise the normal mode transition without requiring a provider login.
+  await dualOutput.setDualOutputMode(status, true);
+  await focusMain();
+}
+
+function testSelectionAfterDisablingDualOutput(horizontalVisible: boolean) {
+  test(`Selection after disabling dual output with horizontal ${
+    horizontalVisible ? 'visible' : 'hidden'
+  }`, async t => {
+    const client = await getApiClient();
+    const scenesService = client.getResource<ScenesService>('ScenesService');
+    const dualOutputService = client.getResource<DualOutputService>('DualOutputService');
+    const selection = client.getResource<SelectionService>('SelectionService');
+    const scene = scenesService.createScene('Selection transition');
+    scenesService.makeSceneActive(scene.id);
+    const horizontalItem = scene.createAndAddSource('Selection target', 'color_source');
+    horizontalItem.fitToScreen();
+
+    await setDualOutputMode(true);
+    dualOutputService.toggleDisplay(horizontalVisible, 'horizontal');
+    const verticalItem = scene.getItems().find(item => item.display === 'vertical');
+    t.truthy(verticalItem, 'Dual output created a vertical partner');
+    t.deepEqual(
+      scene.getSourceSelectorNodes().map(node => node.id),
+      [horizontalVisible ? horizontalItem.id : verticalItem.id],
+      'Dual output source rows follow the visible displays',
+    );
+
+    await setDualOutputMode(false);
+    await waitForDisplayed('#horizontal-display');
+    t.deepEqual(
+      scene.getSourceSelectorNodes().map(node => node.id),
+      [horizontalItem.id],
+      'Single output source rows always use horizontal items',
+    );
+
+    await click('[data-name="Selection target"]');
+    t.deepEqual(selection.getIds(), [horizontalItem.id], 'List selects only the visible item');
+
+    selection.reset();
+    await t.context.app.client.waitUntil(async () => {
+      const selectedRows = await t.context.app.client.$$(
+        '.ant-tree-node-selected [data-name="Selection target"]',
+      );
+      return selectedRows.length === 0;
+    });
+    await click('#horizontal-display');
+    await waitForDisplayed('.ant-tree-node-selected [data-name="Selection target"]');
+    t.deepEqual(selection.getIds(), [horizontalItem.id], 'Canvas selection highlights the list');
+
+    await setDualOutputMode(true);
+    t.is(
+      dualOutputService.state.videoSettings.activeDisplays.horizontal,
+      horizontalVisible,
+      'The saved horizontal display preference is preserved',
+    );
+    t.deepEqual(
+      scene.getSourceSelectorNodes().map(node => node.id),
+      [horizontalVisible ? horizontalItem.id : verticalItem.id],
+      'Re-enabling dual output restores the corresponding source rows',
+    );
+  });
+}
+
 function confirmDualOutputSources(t: TExecutionContext, scene: Scene) {
   const numSceneItems = scene
     .getItems()