fix(desktop): handle Cmd/Ctrl +/-/0 zoom in main process (MUL-2354) (#2791)

The default Electron application menu's zoomIn/zoomOut roles do not fire
reliably on macOS — Cmd+= would zoom in but Cmd+- could not undo it, so
users got stuck at the zoomed-in level with no way back.

Move the shortcut into before-input-event so the same handler covers
every platform and every keyboard layout. preventDefault here blocks
both the renderer keydown and the menu accelerator, so there's no
double-zoom risk on macOS.

Co-authored-by: multica-agent <github@multica.ai>

apps/desktop/src/main/index.ts

@@ -7,6 +7,7 @@ import { setupAutoUpdater } from "./updater";
 import { setupDaemonManager } from "./daemon-manager";
 import { openExternalSafely, downloadURLSafely } from "./external-url";
 import { installContextMenu } from "./context-menu";
+import { handleAppShortcut } from "./keyboard-shortcuts";
 import { getAppVersion } from "./app-version";
 import { loadRuntimeConfig } from "./runtime-config-loader";
 import type { RuntimeConfigResult } from "../shared/runtime-config";
@@ -189,19 +190,13 @@ function createWindow(): void {
     return { action: "deny" };
   });
 
-  // Prevent Cmd+R / Ctrl+R / Shift+Cmd+R / Shift+Ctrl+R / F5 from
-  // reloading the page. In a desktop app an accidental reload destroys
-  // in-memory state (tabs, drafts, WS connections) with no URL bar to
-  // navigate back. DevTools refresh (via the DevTools UI) still works.
-  mainWindow.webContents.on("before-input-event", (_event, input) => {
-    if (input.type !== "keyDown") return;
-    const cmdOrCtrl =
-      process.platform === "darwin" ? input.meta : input.control;
-    if (
-      (cmdOrCtrl && input.key.toLowerCase() === "r") ||
-      input.key === "F5"
-    ) {
-      _event.preventDefault();
+  // Window-level keyboard shortcuts. Calling preventDefault here prevents
+  // both the renderer keydown AND the application menu accelerator, so
+  // anything we own here (reload-block, zoom) is the sole handler for
+  // that combination — no double-fire with the macOS default View menu.
+  mainWindow.webContents.on("before-input-event", (event, input) => {
+    if (handleAppShortcut(input, mainWindow!.webContents)) {
+      event.preventDefault();
     }
   });
 

apps/desktop/src/main/keyboard-shortcuts.test.ts

@@ -0,0 +1,152 @@
+import { describe, expect, it, vi } from "vitest";
+import { handleAppShortcut, type ShortcutInput } from "./keyboard-shortcuts";
+
+function makeWc(initialLevel = 0) {
+  let level = initialLevel;
+  return {
+    getZoomLevel: vi.fn(() => level),
+    setZoomLevel: vi.fn((next: number) => {
+      level = next;
+    }),
+    currentLevel: () => level,
+  };
+}
+
+function key(
+  k: string,
+  mods: Partial<Pick<ShortcutInput, "control" | "meta">> = {},
+): ShortcutInput {
+  return {
+    type: "keyDown",
+    key: k,
+    control: false,
+    meta: false,
+    ...mods,
+  };
+}
+
+describe("handleAppShortcut — reload blocking", () => {
+  it("swallows Cmd+R on macOS", () => {
+    const wc = makeWc();
+    expect(handleAppShortcut(key("r", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.setZoomLevel).not.toHaveBeenCalled();
+  });
+
+  it("swallows Ctrl+R on Linux/Windows", () => {
+    const wc = makeWc();
+    expect(handleAppShortcut(key("r", { control: true }), wc, "linux")).toBe(true);
+    expect(handleAppShortcut(key("R", { control: true }), wc, "win32")).toBe(true);
+  });
+
+  it("swallows F5 regardless of modifier", () => {
+    const wc = makeWc();
+    expect(handleAppShortcut(key("F5"), wc, "darwin")).toBe(true);
+  });
+
+  it("ignores non-keyDown events", () => {
+    const wc = makeWc();
+    expect(
+      handleAppShortcut({ ...key("r", { meta: true }), type: "keyUp" }, wc, "darwin"),
+    ).toBe(false);
+  });
+});
+
+describe("handleAppShortcut — zoom in", () => {
+  it("zooms in on Cmd+= (unshifted)", () => {
+    const wc = makeWc(0);
+    expect(handleAppShortcut(key("=", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("zooms in on Cmd++ (Shift+=)", () => {
+    const wc = makeWc(0);
+    expect(handleAppShortcut(key("+", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("zooms in on Ctrl+= on non-mac", () => {
+    const wc = makeWc(0);
+    expect(handleAppShortcut(key("=", { control: true }), wc, "linux")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("does nothing without Cmd/Ctrl", () => {
+    const wc = makeWc(0);
+    expect(handleAppShortcut(key("="), wc, "darwin")).toBe(false);
+    expect(wc.setZoomLevel).not.toHaveBeenCalled();
+  });
+
+  it("clamps zoom-in at the upper bound", () => {
+    const wc = makeWc(4.5);
+    expect(handleAppShortcut(key("=", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(4.5);
+  });
+});
+
+describe("handleAppShortcut — zoom out (regression: MUL-2354)", () => {
+  it("zooms out on Cmd+- (unshifted)", () => {
+    const wc = makeWc(1);
+    expect(handleAppShortcut(key("-", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("zooms out on Cmd+_ (Shift+-)", () => {
+    const wc = makeWc(1);
+    expect(handleAppShortcut(key("_", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("zooms out on Ctrl+- on non-mac", () => {
+    const wc = makeWc(1);
+    expect(handleAppShortcut(key("-", { control: true }), wc, "win32")).toBe(true);
+    expect(wc.currentLevel()).toBe(0.5);
+  });
+
+  it("undoes a prior Cmd+= so the user can return to 100%", () => {
+    const wc = makeWc(0);
+    handleAppShortcut(key("=", { meta: true }), wc, "darwin");
+    expect(wc.currentLevel()).toBe(0.5);
+    handleAppShortcut(key("-", { meta: true }), wc, "darwin");
+    expect(wc.currentLevel()).toBe(0);
+  });
+
+  it("clamps zoom-out at the lower bound", () => {
+    const wc = makeWc(-3);
+    expect(handleAppShortcut(key("-", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(-3);
+  });
+
+  it("does nothing without Cmd/Ctrl", () => {
+    const wc = makeWc(1);
+    expect(handleAppShortcut(key("-"), wc, "darwin")).toBe(false);
+    expect(wc.setZoomLevel).not.toHaveBeenCalled();
+  });
+});
+
+describe("handleAppShortcut — reset zoom", () => {
+  it("resets to 0 on Cmd+0", () => {
+    const wc = makeWc(2);
+    expect(handleAppShortcut(key("0", { meta: true }), wc, "darwin")).toBe(true);
+    expect(wc.currentLevel()).toBe(0);
+  });
+
+  it("resets to 0 on Ctrl+0", () => {
+    const wc = makeWc(-1.5);
+    expect(handleAppShortcut(key("0", { control: true }), wc, "linux")).toBe(true);
+    expect(wc.currentLevel()).toBe(0);
+  });
+
+  it("ignores plain 0 without modifier", () => {
+    const wc = makeWc(2);
+    expect(handleAppShortcut(key("0"), wc, "darwin")).toBe(false);
+    expect(wc.setZoomLevel).not.toHaveBeenCalled();
+  });
+});
+
+describe("handleAppShortcut — unrelated keys pass through", () => {
+  it("does not capture plain letters", () => {
+    const wc = makeWc();
+    expect(handleAppShortcut(key("a", { meta: true }), wc, "darwin")).toBe(false);
+    expect(handleAppShortcut(key("k", { meta: true }), wc, "darwin")).toBe(false);
+  });
+});

apps/desktop/src/main/keyboard-shortcuts.ts

@@ -0,0 +1,74 @@
+import type { WebContents } from "electron";
+
+// Shape of the input subset we read from Electron's `before-input-event`.
+// Modeled as a structural type so the handler is unit-testable without a
+// real Electron Input instance.
+export type ShortcutInput = {
+  type: string;
+  key: string;
+  control: boolean;
+  meta: boolean;
+};
+
+// Subset of WebContents the zoom handler needs. Keeps the test mock tiny.
+export type ZoomTarget = Pick<WebContents, "getZoomLevel" | "setZoomLevel">;
+
+// Match Electron's built-in zoomIn/zoomOut roles (Chromium default of 0.5
+// per step). Clamp to a range that keeps the UI legible — values outside
+// this band turn the workspace into either confetti or a microfiche.
+const ZOOM_STEP = 0.5;
+const ZOOM_MIN = -3;
+const ZOOM_MAX = 4.5;
+
+/**
+ * Inspect a `before-input-event` key and apply (or block) the matching
+ * window-level shortcut. Returns `true` when the caller should call
+ * `event.preventDefault()` — that both swallows the renderer keydown and
+ * prevents the application menu accelerator from firing, so we don't
+ * double-trigger zoom on macOS where the default menu also binds these
+ * keys.
+ *
+ * Why we don't rely on the menu's `zoomIn` / `zoomOut` roles: on macOS the
+ * default `Cmd+-` accelerator does not fire reliably across keyboard
+ * layouts (issue MUL-2354 — Cmd+= zooms in but Cmd+- doesn't undo it).
+ * Handling the shortcuts here gives identical behavior on every platform
+ * and every layout.
+ */
+export function handleAppShortcut(
+  input: ShortcutInput,
+  webContents: ZoomTarget,
+  platform: NodeJS.Platform = process.platform,
+): boolean {
+  if (input.type !== "keyDown") return false;
+  const cmdOrCtrl = platform === "darwin" ? input.meta : input.control;
+
+  // Block reload — accidental Cmd+R / Ctrl+R / F5 destroys in-memory state
+  // (tabs, drafts, WS connections) with no URL bar to recover from.
+  if ((cmdOrCtrl && input.key.toLowerCase() === "r") || input.key === "F5") {
+    return true;
+  }
+
+  if (!cmdOrCtrl) return false;
+
+  // Cmd/Ctrl + "=" (unshifted) or "+" (Shift+=) → zoom in.
+  if (input.key === "=" || input.key === "+") {
+    const next = Math.min(webContents.getZoomLevel() + ZOOM_STEP, ZOOM_MAX);
+    webContents.setZoomLevel(next);
+    return true;
+  }
+
+  // Cmd/Ctrl + "-" (unshifted) or "_" (Shift+-) → zoom out.
+  if (input.key === "-" || input.key === "_") {
+    const next = Math.max(webContents.getZoomLevel() - ZOOM_STEP, ZOOM_MIN);
+    webContents.setZoomLevel(next);
+    return true;
+  }
+
+  // Cmd/Ctrl + 0 → reset zoom to 100%.
+  if (input.key === "0") {
+    webContents.setZoomLevel(0);
+    return true;
+  }
+
+  return false;
+}