test(transitions): regression lock for the #269 motion guard

src/lib/__tests__/transitions.test.ts

@@ -0,0 +1,56 @@
+import { describe, it, expect, afterEach } from 'vitest';
+import {
+  fadeQuick,
+  modalScale,
+  overlayFade,
+  overlayFlyUp,
+  slideDown,
+  expandSlide,
+  motionSuppressed,
+} from '../transitions';
+
+// Regression lock for #269: in web mode (and whenever the user asks for
+// reduced motion) every shared preset must resolve to a zero-duration
+// transition. Svelte's out-transition completion never fires in background
+// panes, so a real transition there stacked stale views forever.
+
+const node = document.createElement('div');
+
+afterEach(() => {
+  delete (window as any).__TAURI_INTERNALS__;
+});
+
+describe('motion suppression (web mode + reduced motion)', () => {
+  it('is always on in a plain browser', () => {
+    // vitest runs without __TAURI_INTERNALS__ → web mode → suppressed.
+    expect(motionSuppressed()).toBe(true);
+  });
+
+  it('is on for desktop when prefers-reduced-motion is set', () => {
+    (window as any).__TAURI_INTERNALS__ = {};
+    (window as any).matchMedia = (query: string) => ({
+      matches: query.includes('prefers-reduced-motion'),
+      media: query,
+    });
+    expect(motionSuppressed()).toBe(true);
+  });
+
+  it('is off for desktop when the user allows motion', () => {
+    (window as any).__TAURI_INTERNALS__ = {};
+    (window as any).matchMedia = (query: string) => ({
+      matches: false,
+      media: query,
+    });
+    expect(motionSuppressed()).toBe(false);
+  });
+});
+
+describe('presets collapse to zero duration when suppressed', () => {
+  it('every shared preset returns duration 0 in web mode', () => {
+    const presets = [fadeQuick, modalScale, overlayFade, overlayFlyUp, slideDown, expandSlide];
+    for (const preset of presets) {
+      const config = preset(node);
+      expect(config.duration).toBe(0);
+    }
+  });
+});

src/lib/transitions.ts

@@ -3,28 +3,32 @@
 
 import { fade, fly, scale, slide } from 'svelte/transition';
 import type { TransitionConfig } from 'svelte/transition';
-import { isWebMode } from './ts/transport';
 
 type EasingFunc = (t: number) => number;
 
-// Web-mode guard: in a background browser pane, Svelte's out-transition
-// completion callbacks never fire — keyed swaps and overlay closes leave
-// stale DOM stacked forever. A zero-duration no-op keeps the API contract
-// (Svelte requires a function) while finishing instantly; desktop keeps
-// the real presets untouched.
+// Motion suppression guard, checked per-invocation:
+// 1. Web mode (background panes): Svelte's out-transition completion never
+//    fires there, so real transitions stacked stale views forever (#269) —
+//    always suppress.
+// 2. Desktop: animate, unless the user asked for reduced motion.
 const noOp = (): TransitionConfig => ({ duration: 0 });
 const prefersReducedMotion = (): boolean =>
   typeof window !== 'undefined' &&
   typeof window.matchMedia === 'function' &&
   window.matchMedia('(prefers-reduced-motion: reduce)').matches;
+
+/** True when transitions should be skipped entirely. */
+export function motionSuppressed(): boolean {
+  if (typeof window !== 'undefined' && '__TAURI_INTERNALS__' in window) {
+    return prefersReducedMotion();
+  }
+  return true; // plain browser (incl. background panes)
+}
+
 const guarded = <A extends unknown[]>(
   preset: (node: Element, ...args: A) => TransitionConfig,
 ): ((node: Element, ...args: A) => TransitionConfig) => {
-  if (!isWebMode) {
-    // Checked per-invocation so a live OS setting change is respected.
-    return (node, ...args) => (prefersReducedMotion() ? { duration: 0 } : preset(node, ...args));
-  }
-  return (node, ..._args) => ({ duration: 0 });
+  return (node, ...args) => (motionSuppressed() ? { duration: 0 } : preset(node, ...args));
 };
 
 // Easing — cubic-bezier approximations for smooth UI motion