fix(desktop): macOS swipe Back/Forward moves the focused Browser tab

apps/desktop/src/preview/Manager.ts

@@ -488,6 +488,10 @@ const isPreviewRefreshShortcut = (input: Electron.Input, platform: NodeJS.Platfo
   !input.shift &&
   !input.alt;
 
+// Every guest of a focused window reports focus; GuestInput handles guests without a focused frame.
+export const holdsKeyboardFocus = (contents: Electron.WebContents): boolean =>
+  contents.isFocused() && contents.focusedFrame !== null;
+
 export const isPreviewEditingShortcut = (
   input: Electron.Input,
   platform: NodeJS.Platform,
@@ -1444,9 +1448,6 @@ const makeNativeOperations = Effect.fn("PreviewManager.makeOperations")(function
         }).pipe(Effect.ignore),
       );
     };
-    // Every guest of a focused window reports focus; GuestInput handles guests without a focused frame.
-    const holdsKeyboardFocus = (contents: Electron.WebContents) =>
-      contents.isFocused() && contents.focusedFrame !== null;
     const syncMenuShortcuts = (contents: Electron.WebContents, input: Electron.Input): void => {
       if (input.type !== "keyDown") return;
       contents.setIgnoreMenuShortcuts(

apps/desktop/src/window/DesktopWindow.test.ts

@@ -31,6 +31,9 @@ vi.mock("electron", async (importOriginal) => ({
       },
     ]),
   },
+  webContents: {
+    getAllWebContents: vi.fn(() => []),
+  },
 }));
 
 import * as DesktopAssets from "../app/DesktopAssets.ts";
@@ -1044,12 +1047,35 @@ describe("DesktopWindow", () => {
     }),
   );
 
-  it.effect("maps macOS horizontal swipes to available history navigation", () =>
+  it.effect("maps macOS horizontal swipes to the focused Browser tab or the app history", () =>
     Effect.gen(function* () {
       const fakeWindow = makeFakeBrowserWindow();
       const createCount = yield* Ref.make(0);
       const mainWindow = yield* Ref.make<Option.Option<Electron.BrowserWindow>>(Option.none());
       const layer = layerTest({ window: fakeWindow.window, createCount, mainWindow });
+      const guestHistory = {
+        canGoBack: vi.fn(() => true),
+        canGoForward: vi.fn(() => true),
+        goBack: vi.fn(),
+        goForward: vi.fn(),
+      };
+      const guest = {
+        hostWebContents: fakeWindow.window.webContents,
+        isDestroyed: () => false,
+        isFocused: () => true,
+        focusedFrame: {} as Electron.WebFrameMain | null,
+        navigationHistory: guestHistory,
+      };
+      const navigations = () => ({
+        app: [
+          fakeWindow.navigationHistory.goBack.mock.calls.length,
+          fakeWindow.navigationHistory.goForward.mock.calls.length,
+        ],
+        browserTab: [
+          guestHistory.goBack.mock.calls.length,
+          guestHistory.goForward.mock.calls.length,
+        ],
+      });
 
       yield* Effect.gen(function* () {
         const desktopWindow = yield* DesktopWindow.DesktopWindow;
@@ -1060,19 +1086,37 @@ describe("DesktopWindow", () => {
         const history = fakeWindow.navigationHistory;
 
         swipe({}, "left");
-        assert.equal(history.goBack.mock.calls.length, 1);
-        assert.equal(history.goForward.mock.calls.length, 0);
         swipe({}, "right");
-        assert.equal(history.goForward.mock.calls.length, 1);
-
         swipe({}, "up");
         swipe({}, "down");
+        assert.deepEqual(navigations(), { app: [1, 1], browserTab: [0, 0] });
+
+        using _all = vi
+          .mocked(Electron.webContents.getAllWebContents)
+          .mockReturnValue([
+            fakeWindow.window.webContents,
+            guest as unknown as Electron.WebContents,
+          ]);
+        swipe({}, "left");
+        swipe({}, "right");
+        assert.deepEqual(
+          navigations(),
+          { app: [1, 1], browserTab: [1, 1] },
+          "swipe back/forward should navigate the focused Browser tab, not the app router",
+        );
+
+        // Every guest of a focused window reports isFocused(); focus back in the app clears its frame.
+        guest.focusedFrame = null;
         history.canGoBack.mockReturnValue(false);
         history.canGoForward.mockReturnValue(false);
         swipe({}, "left");
         swipe({}, "right");
-        assert.equal(history.goBack.mock.calls.length, 1);
-        assert.equal(history.goForward.mock.calls.length, 1);
+        assert.deepEqual(navigations(), { app: [1, 1], browserTab: [1, 1] });
+        history.canGoBack.mockReturnValue(true);
+        history.canGoForward.mockReturnValue(true);
+        swipe({}, "left");
+        swipe({}, "right");
+        assert.deepEqual(navigations(), { app: [2, 2], browserTab: [1, 1] });
       }).pipe(Effect.provide(layer));
     }),
   );

apps/desktop/src/window/DesktopWindow.ts

@@ -747,7 +747,15 @@ export const make = Effect.gen(function* () {
     if (environment.platform === "darwin") {
       // Mouse drivers can deliver Back/Forward as macOS swipe gestures instead of buttons.
       window.on("swipe", (_event, direction) => {
-        const history = window.webContents.navigationHistory;
+        const focusedGuest = Electron.webContents
+          .getAllWebContents()
+          .find(
+            (contents) =>
+              contents.hostWebContents === window.webContents &&
+              !contents.isDestroyed() &&
+              PreviewManager.holdsKeyboardFocus(contents),
+          );
+        const history = (focusedGuest ?? window.webContents).navigationHistory;
         if (direction === "left" && history.canGoBack()) history.goBack();
         else if (direction === "right" && history.canGoForward()) history.goForward();
       });