diff --git a/apps/web/tests/reasoning-preview.e2e.ts b/apps/web/tests/reasoning-preview.e2e.ts
index 6ae2425e41..15fa2a0988 100644
--- a/apps/web/tests/reasoning-preview.e2e.ts
+++ b/apps/web/tests/reasoning-preview.e2e.ts
@@ -65,39 +65,58 @@ it('shows completed paragraph first lines across blank lines with a right-edge f
       const reasoning = page.locator('[data-variant="think"][data-state="running"]')
       await expandOwningTurnProcess(page, reasoning)
       await reasoning.waitFor()
-      const whale = page.locator('[data-chat-running] svg')
-      const animatedWhale = whale.locator('path:has(animate)')
-      const restingWhale = whale.locator('path:not(:has(animate))')
-      await animatedWhale.locator('animate').waitFor({ state: 'attached' })
-      const positions = await animatedWhale.evaluate(async (element) => {
-        const path = element as SVGPathElement
-        const svg = path.ownerSVGElement!
-        const time = svg.getCurrentTime()
-        svg.pauseAnimations()
-        try {
-          const positions: number[][] = []
-          for (const at of [0.3, 0.9, 3.3]) {
-            svg.setCurrentTime(at)
-            await new Promise<void>(resolve => requestAnimationFrame(() => { resolve() }))
-            const point = path.getPointAtLength(path.getTotalLength() * 0.4)
-            positions.push([point.x, point.y])
-          }
-          return positions
-        } finally {
-          svg.setCurrentTime(time)
-          svg.unpauseAnimations()
-        }
-      })
-      expect(positions[1]).not.toEqual(positions[0])
-      expect(positions[2]).toEqual(positions[0])
-      expect(await animatedWhale.evaluate(element => getComputedStyle(element).display)).not.toBe('none')
-      expect(await restingWhale.evaluate(element => getComputedStyle(element).display)).toBe('none')
-      await page.emulateMedia({ reducedMotion: 'reduce' })
-      await expect.poll(() => animatedWhale.evaluate(element => getComputedStyle(element).display)).toBe('none')
-      await expect.poll(() => restingWhale.evaluate(element => getComputedStyle(element).display)).not.toBe('none')
-      await page.emulateMedia({ reducedMotion: 'no-preference' })
-      await expect.poll(() => animatedWhale.evaluate(element => getComputedStyle(element).display)).not.toBe('none')
-      await expect.poll(() => restingWhale.evaluate(element => getComputedStyle(element).display)).toBe('none')
+      const whale = page.locator('[data-chat-running] span[aria-hidden="true"]:has(> svg)')
+      const animatedWhale = whale.locator(':scope > span')
+      const restingWhale = whale.locator(':scope > svg')
+      await whale.waitFor()
+      expect(await whale.locator('animate').count()).toBe(0)
+      const expectStaticWhale = async () => {
+        await expect.poll(() => animatedWhale.isVisible()).toBe(false)
+        await expect.poll(() => restingWhale.isVisible()).toBe(true)
+        expect(await animatedWhale.evaluate(element => getComputedStyle(element).maskImage)).toBe('none')
+        const colors = await restingWhale.locator('path').evaluate((path) => {
+          const probe = document.createElement('span')
+          probe.style.cssText = 'color: Canvas; forced-color-adjust: none'
+          document.body.append(probe)
+          try {
+            const style = getComputedStyle(path)
+            return {
+              stroke: style.stroke.toLowerCase() === 'currentcolor' ? style.color : style.stroke,
+              canvas: getComputedStyle(probe).color,
+              length: (path as SVGPathElement).getTotalLength(),
+            }
+          } finally { probe.remove() }
+        })
+        expect(colors.stroke).not.toBe('none')
+        expect(colors.stroke).not.toBe('transparent')
+        expect(colors.stroke).not.toBe(colors.canvas)
+        expect(colors.length).toBeGreaterThan(0)
+      }
+      try {
+        await page.emulateMedia({ reducedMotion: 'no-preference', forcedColors: 'none' })
+        await expect.poll(() => animatedWhale.isVisible()).toBe(true)
+        expect(await animatedWhale.evaluate(element => getComputedStyle(element).maskMode)).toBe('alpha')
+        const imageSize = await animatedWhale.evaluate(async (element) => {
+          const source = getComputedStyle(element).maskImage.match(/^url\("?(data:image\/png;base64,[A-Za-z0-9+/=]+)"?\)$/)?.[1]
+          if (source === undefined) throw new Error('Running whale mask must use the bundled PNG data URL')
+          const image = new Image()
+          image.src = source
+          await image.decode()
+          return [image.naturalWidth, image.naturalHeight]
+        })
+        expect(imageSize).toEqual([28, 28])
+        expect(await restingWhale.isVisible()).toBe(false)
+        const firstWhaleFrame = await whale.screenshot({ animations: 'allow' })
+        await expect.poll(async () => !(await whale.screenshot({ animations: 'allow' })).equals(firstWhaleFrame), {
+          timeout: 5000,
+        }).toBe(true)
+        await page.emulateMedia({ reducedMotion: 'reduce' })
+        await expectStaticWhale()
+        await page.emulateMedia({ reducedMotion: 'no-preference', forcedColors: 'active' })
+        await expectStaticWhale()
+      } finally {
+        await page.emulateMedia({ reducedMotion: null, forcedColors: null })
+      }
       expect(await reasoning.getAttribute('data-preview')).toBeNull()
 
       first.proceed.resolve(undefined)
@@ -120,6 +139,7 @@ it('shows completed paragraph first lines across blank lines with a right-edge f
       third.proceed.resolve(undefined)
       await settled
       await page.getByText('Done', { exact: true }).waitFor()
+      await whale.waitFor({ state: 'detached' })
       expect(console.pageErrors).toEqual([])
       expect(console.warnings).toEqual([])
     } finally {
diff --git a/packages/client/ui-chat/src/client/chat/ChatView.module.css b/packages/client/ui-chat/src/client/chat/ChatView.module.css
index 71c13916b4..ff121998a6 100644
--- a/packages/client/ui-chat/src/client/chat/ChatView.module.css
+++ b/packages/client/ui-chat/src/client/chat/ChatView.module.css
@@ -160,32 +160,35 @@
   flex: none;
   width: calc(14px + var(--dsh-content-font-delta, 0px));
   height: calc(14px + var(--dsh-content-font-delta, 0px));
+  /* The fixed footprint contains the animation's layout and paint. */
   contain: strict;
   overflow: hidden;
 }
 
 .runningWhaleAnimated {
+  display: none;
   position: absolute;
   inset: 0;
-  background: currentColor;
-  mask: url('./running-whale@2x.png') center / 100% 100% no-repeat;
-  mask-mode: alpha;
-  will-change: transform;
 }
 
 .runningWhaleStill {
-  display: none;
+  display: initial;
 }
 
-@media (prefers-reduced-motion: reduce) {
-  .runningWhaleAnimated {
-    display: none;
-    mask-image: none;
-    will-change: auto;
-  }
+@supports (mask-mode: alpha) and (mask-image: url('')) {
+  @media (prefers-reduced-motion: no-preference) and (forced-colors: none) {
+    .runningWhaleAnimated {
+      display: block;
+      background: currentColor;
+      mask: url('./running-whale@2x.png') center / 100% 100% no-repeat;
+      mask-mode: alpha;
+      /* Keep animated-mask repaints on an icon-sized composited layer. */
+      will-change: transform;
+    }
 
-  .runningWhaleStill {
-    display: initial;
+    .runningWhaleStill {
+      display: none;
+    }
   }
 }
 
diff --git a/packages/client/ui-chat/tests/chat-view.client.spec.tsx b/packages/client/ui-chat/tests/chat-view.client.spec.tsx
index 932dd53060..ba6d2e0b47 100644
--- a/packages/client/ui-chat/tests/chat-view.client.spec.tsx
+++ b/packages/client/ui-chat/tests/chat-view.client.spec.tsx
@@ -4131,8 +4131,12 @@ describe('ChatView', () => {
     expect(column.lastElementChild).toBe(status)
     expect(within(status as HTMLElement).getByRole('status').textContent).toBe('深度求索中')
     expect(status?.lastElementChild?.textContent).toBe('深度求索中')
-    expect(status?.querySelector('svg')?.parentElement?.getAttribute('aria-hidden')).toBe('true')
-    expect(status?.querySelector('animate')).not.toBeNull()
+    const icon = status?.querySelector('svg')?.parentElement
+    expect(icon?.getAttribute('aria-hidden')).toBe('true')
+    expect(icon?.firstElementChild?.tagName).toBe('SPAN')
+    expect(icon?.querySelectorAll('path')).toHaveLength(1)
+    expect(icon?.getAttribute('style')).toBeNull()
+    expect(status?.querySelector('animate')).toBeNull()
     act(() => { h.setSession({ running: false }) })
     expect(column.querySelector('[data-chat-running]')).toBeNull()
   })
diff --git a/packages/client/ui-chat/tests/running-whale-tail.client.spec.tsx b/packages/client/ui-chat/tests/running-whale-tail.client.spec.tsx
index f2a06bd9a2..5d1bbc0c99 100644
--- a/packages/client/ui-chat/tests/running-whale-tail.client.spec.tsx
+++ b/packages/client/ui-chat/tests/running-whale-tail.client.spec.tsx
@@ -1,5 +1,7 @@
 // @vitest-environment jsdom
 
+import { readFileSync } from 'node:fs'
+import { resolve } from 'node:path'
 import { cleanup, render } from '@testing-library/react'
 import { afterEach, describe, expect, it } from 'vitest'
 import { RunningWhaleTail } from '../src/client/chat/RunningWhaleTail.tsx'
@@ -7,26 +9,55 @@ import { RunningWhaleTail } from '../src/client/chat/RunningWhaleTail.tsx'
 afterEach(cleanup)
 
 describe('RunningWhaleTail', () => {
-  it('renders matching animated and resting contours for the stylesheet to switch', () => {
+  it('renders a decorative mask seat and static SVG without inline styles', () => {
     const view = render(<RunningWhaleTail />)
-    expect(view.container.firstElementChild?.getAttribute('aria-hidden')).toBe('true')
-    expect(view.container.querySelector('svg')?.getAttribute('viewBox')).toBe('0 0 16 16')
-    const contours = view.container.querySelectorAll('path')
-    expect(contours).toHaveLength(2)
-    expect(contours[1]?.getAttribute('d')).toBe(contours[0]?.getAttribute('d'))
-    const animation = view.container.querySelector('animate')
-    expect(animation?.getAttribute('attributeName')).toBe('d')
-    expect(animation?.getAttribute('begin')).toBe('0.3s')
-    expect(animation?.getAttribute('dur')).toBe('3s')
-    expect(animation?.getAttribute('repeatCount')).toBe('indefinite')
-    const paths = animation!.getAttribute('values')!.split(';')
-    const times = animation!.getAttribute('keyTimes')!.split(';').map(Number)
-    expect(paths.length).toBeGreaterThan(1)
-    expect(paths).toHaveLength(times.length)
-    expect(paths[0]).toBe(view.container.querySelector('path')?.getAttribute('d'))
-    expect(paths.at(-1)).toBe(paths[0])
-    expect(times[0]).toBe(0)
-    expect(times.at(-1)).toBe(1)
-    expect(times.slice(1).every((time, i) => time > times[i]!)).toBe(true)
+    const icon = view.container.firstElementChild!
+    expect(icon.tagName).toBe('SPAN')
+    expect(icon.getAttribute('aria-hidden')).toBe('true')
+    expect(icon.children).toHaveLength(2)
+    expect(icon.firstElementChild?.tagName).toBe('SPAN')
+    expect(icon.firstElementChild?.childElementCount).toBe(0)
+    const svg = icon.querySelector('svg')!
+    expect(icon.lastElementChild).toBe(svg)
+    expect(svg.getAttribute('viewBox')).toBe('0 0 16 16')
+    expect(svg.querySelectorAll('path')).toHaveLength(1)
+    expect(svg.querySelector('path')?.getAttribute('d')).toMatch(/^M/)
+    expect(svg.querySelector('path')?.getAttribute('stroke')).toBe('currentColor')
+    expect(view.container.querySelector('animate')).toBeNull()
+    expect(view.container.querySelector('[style]')).toBeNull()
+  })
+
+  it('ships a 28px alpha APNG with sixty 50ms frames and infinite playback', () => {
+    const png = readFileSync(resolve(import.meta.dirname, '../src/client/chat/running-whale@2x.png'))
+    expect([...png.subarray(0, 8)]).toEqual([137, 80, 78, 71, 13, 10, 26, 10])
+    const chunks: { type: string; data: Buffer }[] = []
+    for (let offset = 8; offset < png.length;) {
+      const length = png.readUInt32BE(offset)
+      const end = offset + 12 + length
+      expect(end).toBeLessThanOrEqual(png.length)
+      chunks.push({ type: png.toString('ascii', offset + 4, offset + 8), data: png.subarray(offset + 8, end - 4) })
+      offset = end
+    }
+    expect(chunks.at(-1)?.type).toBe('IEND')
+    const headers = chunks.filter(chunk => chunk.type === 'IHDR')
+    expect(headers).toHaveLength(1)
+    const header = headers[0]!.data
+    expect([header.readUInt32BE(0), header.readUInt32BE(4), header[8], header[9]]).toEqual([28, 28, 8, 4])
+    const animations = chunks.filter(chunk => chunk.type === 'acTL')
+    expect(animations).toHaveLength(1)
+    expect([animations[0]!.data.readUInt32BE(0), animations[0]!.data.readUInt32BE(4)]).toEqual([60, 0])
+    const frames = chunks.filter(chunk => chunk.type === 'fcTL')
+    expect(frames).toHaveLength(60)
+    let duration = 0
+    for (const { data } of frames) {
+      expect(data).toHaveLength(26)
+      expect(data.readUInt32BE(4)).toBeGreaterThan(0)
+      expect(data.readUInt32BE(8)).toBeGreaterThan(0)
+      expect(data.readUInt32BE(4) + data.readUInt32BE(12)).toBeLessThanOrEqual(28)
+      expect(data.readUInt32BE(8) + data.readUInt32BE(16)).toBeLessThanOrEqual(28)
+      expect([data.readUInt16BE(20), data.readUInt16BE(22)]).toEqual([1, 20])
+      duration += data.readUInt16BE(20) / data.readUInt16BE(22)
+    }
+    expect(duration).toBeCloseTo(3)
   })
 })