diff --git a/apps/desktop/e2e/fixtures.ts b/apps/desktop/e2e/fixtures.ts
index 02130965c3..53020800d5 100644
--- a/apps/desktop/e2e/fixtures.ts
+++ b/apps/desktop/e2e/fixtures.ts
@@ -572,7 +572,6 @@ type E2eTestFixtures = {
   railRenderWindow: Page;
   promptRailWindow: Page;
   partialHistoryWindow: Page;
-  promptRailMotionWindow: Page;
   requestHeaderRowWindow: Page;
   newTaskTargetWindow: Page;
   directoryReferenceWindow: { page: Page; folder: string };
@@ -741,8 +740,9 @@ export const test = base.extend<E2eTestFixtures, E2eWorkerFixtures>({
       await use({ app, page, viewport });
     });
   }, { scope: 'worker' }],
-  // A multi-prompt transcript for the prompt anchor rail. Shown, because every
-  // assertion in prompt-rail.spec.ts is geometry the compositor has to settle.
+  // A multi-prompt transcript. Shown, because the perf suite that measures it
+  // reads real frame pacing, and a throttled compositor paces nothing a user
+  // would see.
   promptRailWindow: async ({ promptRailWorker }, use) => {
     await setPromptRailWindowVisible(promptRailWorker, true);
     try {
@@ -763,28 +763,6 @@ export const test = base.extend<E2eTestFixtures, E2eWorkerFixtures>({
       showWindow: true,
     }, use);
   },
-  // The same transcript, scrolling the way the shipped app scrolls. Separate
-  // from `promptRailWindow` because it is only the jump that needs a scroll
-  // still in flight, and paying for one everywhere costs several seconds per
-  // window and settles less predictably.
-  promptRailMotionWindow: async ({}, use) => {
-    await withE2eWindow({
-      seed: false,
-      // The transcript and the fixture attributes arrive on two unordered
-      // async paths: `runDeferredStartupRefreshes` fires `refreshSessions()`
-      // and `applyE2eFixture()` side by side, and only the second one — after
-      // its `e2eFixture.getState()` IPC resolves — writes
-      // `data-maka-scroll-motion`. A turn can therefore paint while the
-      // document still says nothing about scroll motion. Requiring both in one
-      // selector is what makes "this window scrolls smoothly" true by the time
-      // a test body reads it.
-      readinessSelector: 'html[data-maka-scroll-motion="smooth"] [data-turn-id]',
-      e2eFixtureScenario: 'chat-prompt-rail',
-      locale: 'zh',
-      showWindow: true,
-      scrollMotion: 'smooth',
-    }, use);
-  },
   // Settings → 模型, where `no-models` is the seeded openai-compatible relay —
   // the connection type whose detail page owns the custom request headers
   // editor. Shown, because what this window is for is a rendered box
diff --git a/apps/desktop/e2e/prompt-rail.spec.ts b/apps/desktop/e2e/prompt-rail.spec.ts
deleted file mode 100644
index 7af51a35c2..0000000000
--- a/apps/desktop/e2e/prompt-rail.spec.ts
+++ /dev/null
@@ -1,622 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-import { PROMPT_RAIL_PROMPT_COUNT } from '../src/main/e2e-fixture/seed-helpers';
-import { DESKTOP_TRANSCRIPT_ACTIVE_RANGE_MAX_TURNS } from '../src/preload/transcript-contract';
-import { COMPOSER_INPUT, ensureSidebarExpanded, expect, test } from './fixtures';
-import type { Page } from '@playwright/test';
-
-const MAX_PROMPT_RAIL_TICKS = 64;
-
-/**
- * The prompt anchor rail (#563) has failed three times in a row in the same
- * way: the code kept working and the pixels stopped. #2161 pinned it against
- * `.maka-chat-shell` while Astryx's ChatLayout owned the scroll container, so
- * the rail laid out across the whole conversation and scrolled off screen.
- * #2338 parked it under macOS's overlay scrollbar, which takes no layout space
- * but still swallows the pointer, so every tick rendered and none could be
- * clicked. #2580 moved the tick onto Astryx's `Button`, whose label span put
- * the tick's bar back into normal flow — an inline box takes no width or
- * height, so the bars computed to 0x0 and the rail shipped invisible in 0.1.9
- * and 0.1.10.
- *
- * None of the three is visible to a static read of the CSS, and none is
- * reachable from jsdom, which has no layout. Only a real scroller with a real
- * transcript can see them, so this file keeps one test per failure and nothing
- * else. It is deliberately much smaller than the suite deleted in #2462.
- *
- * Two boundaries worth knowing before adding to it:
- *  - e2e-fixture renders carry `data-maka-e2e-fixture`, and `base.css` gives
- *    that `animation: none` plus a 0.01ms transition cap, so a fixture's state
- *    never depends on when it settles. Assert the end states motion resolves
- *    to; there is no way to assert that anything animated.
- *  - the reachability test is load-bearing on macOS only. Linux's in-flow
- *    scrollbar moves the content column left instead of overlaying it, so the
- *    #2338 regression goes green on CI. Run this spec on macOS before merging
- *    anything that touches the rail's right edge.
- */
-
-const RAIL_PROBE = `(() => {
-  const scroller = document.querySelector('[data-chat-scroll-container="true"]');
-  const rail = document.querySelector('.maka-prompt-rail');
-  if (!scroller || !rail) return null;
-  const s = scroller.getBoundingClientRect();
-  const r = rail.getBoundingClientRect();
-  // Astryx renders the composer dock as the scroll container's last child;
-  // the rail measures it the same way, for want of a published hook.
-  const dock = scroller.lastElementChild.getBoundingClientRect();
-  return {
-    // Positive on all four = the rail's box is inside the scrollport and clear
-    // of the band the sticky dock occupies at the bottom.
-    insetTop: Math.round(r.top - s.top),
-    insetBottom: Math.round(s.bottom - r.bottom),
-    insetRight: Math.round(s.right - r.right),
-    dockClearance: Math.round(dock.top - r.bottom),
-    railWidth: Math.round(r.width),
-    scrollTop: Math.round(scroller.scrollTop),
-  };
-})()`;
-
-interface RailProbe {
-  insetTop: number;
-  insetBottom: number;
-  insetRight: number;
-  dockClearance: number;
-  railWidth: number;
-  scrollTop: number;
-}
-
-function probeRail(page: Page): Promise<RailProbe | null> {
-  return page.evaluate(RAIL_PROBE) as Promise<RailProbe | null>;
-}
-
-async function scrollTranscriptTo(page: Page, position: 'top' | 'bottom'): Promise<void> {
-  await page.evaluate((where) => {
-    const scroller = document.querySelector('[data-chat-scroll-container="true"]');
-    if (!scroller) throw new Error('the chat scroll container is missing');
-    scroller.scrollTop = where === 'top' ? 0 : scroller.scrollHeight;
-  }, position);
-  await notifyTranscriptScrolled(page);
-  await waitForPaintedFrames(page);
-}
-
-async function scrollTranscriptAwayFromTail(page: Page): Promise<void> {
-  await page.evaluate(() => {
-    const root = document.querySelector<HTMLElement>('[data-chat-scroll-container="true"]');
-    if (!root) throw new Error('the chat scroll container is missing');
-    const historyLoadBand = Math.max(640, root.clientHeight * 2);
-    root.scrollTop = Math.min(
-      root.scrollHeight - root.clientHeight - 100,
-      historyLoadBand + 200,
-    );
-    root.dispatchEvent(new Event('scroll'));
-  });
-  await waitForPaintedFrames(page);
-}
-
-async function waitForPaintedFrames(page: Page, count = 2): Promise<void> {
-  await page.evaluate((frames) => new Promise<void>((resolve) => {
-    const tick = (left: number) => {
-      if (left <= 0) {
-        resolve();
-        return;
-      }
-      requestAnimationFrame(() => tick(left - 1));
-    };
-    tick(frames);
-  }), count);
-}
-
-function notifyTranscriptScrolled(page: Page): Promise<void> {
-  return page.evaluate(() => {
-    const root = document.querySelector<HTMLElement>('[data-chat-scroll-container="true"]');
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.dispatchEvent(new Event('scroll'));
-  });
-}
-
-interface ActivePromptRailSnapshot {
-  currentIds: string[];
-  expectedId: string | null;
-  sourceTurnId: string | null;
-}
-
-async function activePromptRailSnapshot(page: Page): Promise<ActivePromptRailSnapshot> {
-  return page.evaluate(async ({ promptCount }) => {
-    const root = document.querySelector<HTMLElement>('[data-chat-scroll-container="true"]');
-    if (!root) throw new Error('the chat scroll container is missing');
-    const ticks = [...document.querySelectorAll<HTMLElement>('.maka-prompt-rail-tick')];
-    const currentIds = ticks
-      .filter((tick) => tick.getAttribute('aria-current') === 'true')
-      .map((tick) => tick.dataset.promptTurnId ?? '');
-    const rootBounds = root.getBoundingClientRect();
-    const atEnd = root.scrollHeight - root.scrollTop - root.clientHeight <= 2;
-    const turns = [...root.querySelectorAll<HTMLElement>('[data-transcript-turn-id]')]
-      .map((turn) => ({
-        element: turn,
-        id: turn.dataset.transcriptTurnId ?? '',
-        index: Number(turn.dataset.transcriptTurnId?.split('-').at(-1)) - 1,
-      }))
-      .filter((turn) => turn.id.length > 0 && Number.isFinite(turn.index));
-    const readingBandTurns = turns
-      .filter(({ element }) => {
-        const bounds = element.getBoundingClientRect();
-        return bounds.bottom > rootBounds.top
-          && bounds.top < rootBounds.top + rootBounds.height * 0.34;
-      })
-      .sort((left, right) => left.index - right.index);
-    const scrollportTurns = turns
-      .filter(({ element }) => {
-        const bounds = element.getBoundingClientRect();
-        return bounds.bottom > rootBounds.top && bounds.top < rootBounds.bottom;
-      })
-      .sort((left, right) => left.index - right.index);
-    const sourceTurn = atEnd
-      ? turns.reduce<typeof turns[number] | null>(
-        (latest, turn) => latest === null || turn.index > latest.index ? turn : latest,
-        null,
-      )
-      : readingBandTurns[0] ?? scrollportTurns[0] ?? null;
-    const expectedRailIndex = sourceTurn === null || ticks.length === 0
-      ? null
-      : Math.round(
-        sourceTurn.index * (ticks.length - 1) / (promptCount - 1),
-      );
-    const expectedId = expectedRailIndex === null
-      ? null
-      : ticks[expectedRailIndex]?.dataset.promptTurnId ?? null;
-    return {
-      currentIds,
-      expectedId,
-      sourceTurnId: sourceTurn?.id ?? null,
-    };
-  }, { promptCount: PROMPT_RAIL_PROMPT_COUNT });
-}
-
-async function expectPromptRailMatchesReadingPosition(page: Page): Promise<void> {
-  let lastSnapshot: ActivePromptRailSnapshot | null = null;
-  try {
-    await expect.poll(async () => {
-      lastSnapshot = await activePromptRailSnapshot(page);
-      return lastSnapshot.expectedId !== null
-        && lastSnapshot.currentIds.length === 1
-        && lastSnapshot.currentIds[0] === lastSnapshot.expectedId;
-    }, { message: 'the one current tick maps from the Turn being read' }).toBe(true);
-  } catch {
-    throw new Error(`the prompt rail did not settle on the reading position: ${JSON.stringify(lastSnapshot)}`);
-  }
-  const snapshot = await activePromptRailSnapshot(page);
-  expect(snapshot.expectedId, `no visible Turn in ${JSON.stringify(snapshot)}`).not.toBeNull();
-  expect(snapshot.currentIds).toEqual([snapshot.expectedId]);
-}
-
-async function scrollTranscriptThroughHistory(page: Page): Promise<void> {
-  for (let pageIndex = 0; pageIndex < PROMPT_RAIL_PROMPT_COUNT; pageIndex += 1) {
-    const firstBefore = await page.locator('[data-turn-id]').first().getAttribute('data-turn-id');
-    if (firstBefore === 'turn-prompt-rail-1') return;
-    await page.evaluate(() => {
-      const root = document.querySelector<HTMLElement>('[data-chat-scroll-container="true"]');
-      if (!root) throw new Error('the chat scroll container is missing');
-      root.scrollTop = 0;
-      root.dispatchEvent(new WheelEvent('wheel', { deltaY: -120, bubbles: true }));
-      root.dispatchEvent(new Event('scroll'));
-    });
-    await expect.poll(async () =>
-      page.locator('[data-turn-id]').first().getAttribute('data-turn-id'), {
-      message: `history loads before ${firstBefore}`,
-      timeout: 20_000,
-    }).not.toBe(firstBefore);
-    await waitForPaintedFrames(page);
-    await expectPromptRailMatchesReadingPosition(page);
-  }
-  throw new Error('the first prompt did not enter the active transcript range');
-}
-
-test('every tick paints a bar with a real box', async ({ promptRailWindow: page }) => {
-  // Measured over ALL ticks, not a sample: a helper that skips what it cannot
-  // evaluate creates its blind spot exactly where a regression lives.
-  const bars = await page.evaluate(() =>
-    [...document.querySelectorAll('.maka-prompt-rail-tick-bar')].map((bar) => {
-      const box = bar.getBoundingClientRect();
-      return { width: Math.round(box.width), height: Math.round(box.height) };
-    }),
-  );
-
-  expect(bars).toHaveLength(Math.min(PROMPT_RAIL_PROMPT_COUNT, MAX_PROMPT_RAIL_TICKS));
-  // #2580 shipped bars at 0x0 — present in the DOM, painting nothing.
-  expect(Math.min(...bars.map((bar) => bar.width))).toBeGreaterThan(0);
-  expect(Math.min(...bars.map((bar) => bar.height))).toBeGreaterThan(0);
-});
-
-test('the rail stays inside the scrollport at both scroll extremes', async ({
-  promptRailWindow: page,
-}) => {
-  const scroll = await page.evaluate(() => {
-    const scroller = document.querySelector('[data-chat-scroll-container="true"]');
-    if (!scroller) throw new Error('the chat scroll container is missing');
-    return { height: scroller.scrollHeight, client: scroller.clientHeight };
-  });
-  // Without an overflowing transcript the rail has nothing to be pinned
-  // against and the rest of this test proves nothing.
-  expect(scroll.height).toBeGreaterThan(scroll.client);
-
-  for (const position of ['top', 'bottom'] as const) {
-    await scrollTranscriptTo(page, position);
-    // The bottom is where it bites: a sticky offset is clamped by its
-    // containing block, and the chat shell ends a dock-height above the
-    // scrollport's bottom edge (CI caught -62px insetTop that way).
-    await expect
-      .poll(async () => {
-        const probe = await probeRail(page);
-        if (!probe) return null;
-        return {
-          insetTop: probe.insetTop >= 0,
-          insetBottom: probe.insetBottom >= 0,
-          insetRight: probe.insetRight >= 0,
-          dockClearance: probe.dockClearance >= 0,
-        };
-      }, { message: `rail geometry at the ${position} of the transcript` })
-      .toEqual({
-        insetTop: true,
-        insetBottom: true,
-        insetRight: true,
-        dockClearance: true,
-      });
-  }
-});
-
-test('the pointer is always on a tick while it travels down the rail', async ({
-  promptRailWindow: page,
-}) => {
-  // The hover falloff reads which tick the pointer entered. A gap between the
-  // hit boxes is a band where it is over the rail and over no tick, so the
-  // effect drops out and picks up again every few pixels of travel. Walked a
-  // pixel at a time rather than sampled between two ticks: a single midpoint
-  // would pass on a rail whose gaps sat anywhere else.
-  const travel = await page.evaluate(() => {
-    const bars = [...document.querySelectorAll('.maka-prompt-rail-tick-bar')];
-    if (bars.length < 2) throw new Error('the prompt rail needs at least two ticks');
-    const first = bars[0]!.getBoundingClientRect();
-    const last = bars[bars.length - 1]!.getBoundingClientRect();
-    const x = Math.round(first.left + first.width / 2);
-    const misses: number[] = [];
-    for (let y = Math.round(first.top + first.height / 2); y <= Math.round(last.top + last.height / 2); y += 1) {
-      const found = document.elementFromPoint(x, y);
-      if (!found?.closest('.maka-prompt-rail-tick')) misses.push(y);
-    }
-    return { misses: misses.length, span: Math.round(last.bottom - first.top) };
-  });
-
-  expect(travel.span).toBeGreaterThan(0);
-  expect(travel.misses).toBe(0);
-});
-
-test('the first click of a session lands on its prompt and holds', async ({
-  promptRailMotionWindow: page,
-}) => {
-  // Clicked before anything else touches the transcript, which is the case
-  // that used to fail: the head of a 30-prompt session is not mounted yet, so
-  // the jump has to mount it, and the fill that follows changes scrollHeight
-  // under Astryx's auto-follow lock. The lock ignores scroll-ups that arrive
-  // with a changed height, so it stayed on and pulled the transcript back to
-  // the bottom — the click looked dead until the reader scrolled by hand.
-  //
-  // This window is the only one in the suite that scrolls smoothly, which is
-  // why it is its own fixture. Every capture otherwise collapses scroll
-  // motion, and a jump that finishes in one frame is never in flight long
-  // enough to meet the lock at all. `emulateMedia` cannot arrange it: the
-  // collapse is keyed on `data-maka-e2e-fixture`, not on the media query.
-  expect(await page.evaluate(() => document.documentElement.dataset.makaScrollMotion)).toBe(
-    'smooth',
-  );
-
-  // The first tick's turn, named rather than inferred: the first mounted
-  // `[data-turn-id]` is whatever the tail window happens to hold, and at the
-  // opening scroll position its top is already above the scrollport, which
-  // passes an upper-bound-only check without the jump doing anything at all.
-  const targetTurnId = 'turn-prompt-rail-1';
-  await page.locator('.maka-prompt-rail-tick').first().click({ force: true });
-
-  const landing = async () =>
-    page.evaluate((turnId) => {
-      const scroller = document.querySelector('[data-chat-scroll-container="true"]')!;
-      const turn = document.querySelector(`[data-turn-id="${turnId}"]`);
-      if (!turn) return null;
-      const tick = document.querySelector('.maka-prompt-rail-tick');
-      return {
-        offset: Math.round(
-          turn.getBoundingClientRect().top - scroller.getBoundingClientRect().top,
-        ),
-        tickIsCurrent: tick?.getAttribute('aria-current') === 'true',
-      };
-    }, targetTurnId);
-
-  // Bounded on both sides: below is the turn never arriving, above is it
-  // arriving and then being pulled off the top of the scrollport.
-  await expect
-    .poll(async () => {
-      const offset = (await landing())?.offset;
-      return offset === undefined ? Number.POSITIVE_INFINITY : Math.abs(offset);
-    }, { message: 'the clicked prompt reaches the top' })
-    .toBeLessThan(24);
-  expect((await landing())?.tickIsCurrent).toBe(true);
-
-  // And stays: turns keep resolving their content and remeasuring after the
-  // jump, so a jump that only wins the first frame reads as landing and then
-  // sliding away.
-  await page.waitForTimeout(1_200);
-  const settled = await landing();
-  expect(settled?.offset).toBeGreaterThan(-24);
-  expect(settled?.offset).toBeLessThan(24);
-  expect(settled?.tickIsCurrent).toBe(true);
-});
-
-test('manual transcript scrolling keeps exactly the visible prompt current', async ({
-  promptRailWindow: page,
-}) => {
-  await page.setViewportSize({ width: 1_000, height: 700 });
-  await scrollTranscriptTo(page, 'bottom');
-  await expectPromptRailMatchesReadingPosition(page);
-  await expect(page.locator('.maka-prompt-rail-tick[aria-current="true"]')).toHaveCount(1);
-  await expect(page.locator('.maka-prompt-rail-tick').last()).toHaveAttribute(
-    'aria-current',
-    'true',
-  );
-
-  await page.evaluate(() => {
-    const rail = document.querySelector('.maka-prompt-rail');
-    if (!rail) throw new Error('the prompt rail is missing');
-    const counts: number[] = [];
-    const record = () => counts.push(
-      rail.querySelectorAll('.maka-prompt-rail-tick[aria-current="true"]').length,
-    );
-    const observer = new MutationObserver(record);
-    observer.observe(rail, {
-      attributes: true,
-      subtree: true,
-      attributeFilter: ['aria-current'],
-    });
-    record();
-    Object.assign(window, {
-      __makaPromptRailCurrentCounts: counts,
-      __makaPromptRailCurrentObserver: observer,
-    });
-  });
-
-  await scrollTranscriptThroughHistory(page);
-  await scrollTranscriptTo(page, 'top');
-  await expectPromptRailMatchesReadingPosition(page);
-  await expect(page.locator('.maka-prompt-rail-tick[aria-current="true"]')).toHaveCount(1);
-  await expect(page.locator('.maka-prompt-rail-tick').first()).toHaveAttribute(
-    'aria-current',
-    'true',
-  );
-
-  const currentCounts = await page.evaluate(() => {
-    const state = window as Window & {
-      __makaPromptRailCurrentCounts?: number[];
-      __makaPromptRailCurrentObserver?: MutationObserver;
-    };
-    state.__makaPromptRailCurrentObserver?.disconnect();
-    return state.__makaPromptRailCurrentCounts ?? [];
-  });
-  expect(currentCounts.length).toBeGreaterThan(1);
-  expect(currentCounts.every((count) => count === 1), currentCounts.join(',')).toBe(true);
-});
-
-test('streaming deltas do not reconstruct the prompt rail observer', async ({
-  window: page,
-}) => {
-  const composer = page.locator(COMPOSER_INPUT);
-  const sendAndSettle = async (prompt: string, expectedTurns: number): Promise<void> => {
-    await composer.fill(prompt);
-    await composer.press('Enter');
-    await expect(page.getByRole('button', { name: '重新生成' })).toHaveCount(expectedTurns, {
-      timeout: 20_000,
-    });
-  };
-  await sendAndSettle('First prompt rail observer seed', 1);
-  await sendAndSettle('Second prompt rail observer seed', 2);
-
-  await page.evaluate(() => {
-    const NativeIntersectionObserver = window.IntersectionObserver;
-    const state: {
-      constructions: number;
-      initialConstructions: number | null;
-    } = { constructions: 0, initialConstructions: null };
-    window.IntersectionObserver = class extends NativeIntersectionObserver {
-      constructor(
-        callback: IntersectionObserverCallback,
-        options?: IntersectionObserverInit,
-      ) {
-        super(callback, options);
-        if (
-          options?.root === document.querySelector('[data-chat-scroll-container="true"]')
-          && options.rootMargin === '0px 0px -66% 0px'
-        ) {
-          state.constructions += 1;
-          state.initialConstructions ??= state.constructions;
-        }
-      }
-    };
-    Object.assign(window, { __makaPromptRailObserverProbe: state });
-  });
-
-  const streamingPrompt = Array.from(
-    { length: 40 },
-    (_, index) => `Observer stability line ${index + 1}`,
-  ).join('\n');
-  await composer.fill(streamingPrompt);
-  await composer.press('Enter');
-
-  await expect.poll(() => page.evaluate(() => (
-    window as Window & {
-      __makaPromptRailObserverProbe?: { constructions: number };
-    }
-  ).__makaPromptRailObserverProbe?.constructions ?? 0), {
-    message: 'the third Turn creates the prompt rail observer',
-  }).toBeGreaterThan(0);
-
-  // The fake backend emits nine characters per delta, so reaching the last
-  // line proves many same-Turn text updates landed after observer creation.
-  await expect(page.getByRole('log').getByText(
-    /Fake backend received:[\s\S]*Observer stability line 40/,
-  )).toBeVisible({
-    timeout: 20_000,
-  });
-
-  const settled = await page.evaluate(() => ({ ...(
-    window as Window & {
-      __makaPromptRailObserverProbe: {
-        constructions: number;
-        initialConstructions: number | null;
-      };
-    }
-  ).__makaPromptRailObserverProbe }));
-  expect(settled.constructions).toBe(settled.initialConstructions);
-});
-
-test('active transcript Turns keep stable DOM identities while scrolling', async ({
-  promptRailWindow: page,
-}) => {
-  const sourceCount = Number(
-    await page.locator('.maka-chat-message-list').getAttribute('data-turn-source-count'),
-  );
-  expect(sourceCount).toBe(DESKTOP_TRANSCRIPT_ACTIVE_RANGE_MAX_TURNS);
-  expect(await page.locator('[data-turn-id]').count()).toBe(sourceCount);
-  await page.evaluate(() => {
-    for (const turn of document.querySelectorAll<HTMLElement>('[data-turn-id]')) {
-      turn.dataset.stableMountProbe = turn.dataset.turnId;
-    }
-  });
-
-  await scrollTranscriptTo(page, 'bottom');
-  await scrollTranscriptAwayFromTail(page);
-
-  expect(await page.locator('[data-turn-id]').count()).toBe(sourceCount);
-  expect(await page.locator('[data-turn-id][data-stable-mount-probe]').count()).toBe(sourceCount);
-});
-
-test('scrolling away preserves a turn-owned focus and selection', async ({
-  promptRailWindow: page,
-}) => {
-  await scrollTranscriptTo(page, 'bottom');
-  await expect(page.locator('[data-turn-id="turn-prompt-rail-120"]')).toHaveCount(1);
-  await page.evaluate(() => {
-    const turn = document.querySelector<HTMLElement>('[data-turn-id="turn-prompt-rail-120"]');
-    if (!turn) throw new Error('the tail Turn is missing');
-    const turnOwnedAction = document.createElement('button');
-    turnOwnedAction.dataset.turnOwnedAction = 'true';
-    turnOwnedAction.textContent = 'Turn-owned action';
-    turn.append(turnOwnedAction);
-    turnOwnedAction.focus();
-    const range = document.createRange();
-    range.selectNodeContents(turnOwnedAction);
-    const selection = document.getSelection();
-    selection?.removeAllRanges();
-    selection?.addRange(range);
-  });
-  await scrollTranscriptAwayFromTail(page);
-
-  await expect.poll(async () => page.evaluate(() => {
-    const active = document.activeElement;
-    return {
-      retained: document.querySelector('[data-turn-id="turn-prompt-rail-120"]') !== null,
-      focusRetained: active instanceof HTMLElement
-        && active.dataset.turnOwnedAction === 'true',
-      selectionRetained: document.getSelection()?.isCollapsed === false,
-    };
-  })).toEqual({
-    retained: true,
-    focusRetained: true,
-    selectionRetained: true,
-  });
-});
-
-test('offscreen active Turns remain findable and accessible', async ({
-  promptRailWindow: page,
-}) => {
-  const firstTurnId = await page.locator('[data-turn-id]').first().getAttribute('data-turn-id');
-  const turnNumber = Number(firstTurnId?.split('-').at(-1));
-  expect(turnNumber).toBeGreaterThan(0);
-  const needle = `第 ${turnNumber} 个问题`;
-  await scrollTranscriptTo(page, 'bottom');
-
-  const found = await page.evaluate((text) => {
-    document.getSelection()?.removeAllRanges();
-    return (window as Window & { find(text: string): boolean }).find(text);
-  }, needle);
-  expect(found).toBe(true);
-  expect(await page.evaluate(() => document.getSelection()?.toString() ?? '')).toContain(needle);
-
-  const cdp = await page.context().newCDPSession(page);
-  const tree = await cdp.send('Accessibility.getFullAXTree');
-  expect(tree.nodes.some((node) => node.name?.value?.includes(needle))).toBe(true);
-});
-
-test('switching sessions reconstructs only the Host active range', async ({
-  promptRailWindow: page,
-}) => {
-  await ensureSidebarExpanded(page);
-  const rows = page.locator('.maka-session-row');
-  const selected = rows.locator('button.astryx-side-nav-item.selected');
-  const originalId = await selected
-    .evaluate((button) => button.closest('.maka-session-row')?.getAttribute('data-session-id'));
-  if (!originalId) throw new Error('the prompt-rail Session is not selected');
-  const otherId = await rows.evaluateAll(
-    (rows, selected) => rows
-      .map((row) => row.getAttribute('data-session-id'))
-      .find((sessionId) => sessionId !== selected) ?? null,
-    originalId,
-  );
-  if (!otherId) throw new Error('the fixture has no second Session');
-  await page.locator(`.maka-session-row[data-session-id=${JSON.stringify(otherId)}] button`)
-    .first()
-    .click();
-  await expect(page.locator(
-    `.maka-session-row[data-session-id=${JSON.stringify(otherId)}] button.selected`,
-  ))
-    .toHaveCount(1);
-
-  await page.locator(`.maka-session-row[data-session-id=${JSON.stringify(originalId)}] button`)
-    .first()
-    .click();
-  await expect(page.locator('[data-turn-id="turn-prompt-rail-120"]')).toHaveCount(1);
-  expect(await page.locator('[data-turn-id]').count())
-    .toBe(DESKTOP_TRANSCRIPT_ACTIVE_RANGE_MAX_TURNS);
-});
-
-test('a tick is what the pointer lands on, not the scrollbar', async ({
-  promptRailWindow: page,
-}) => {
-  // `elementFromPoint`, not `hover()`: dispatched events cannot see occlusion,
-  // and macOS's overlay scrollbar occludes without taking layout space.
-  const hit = await page.evaluate(() => {
-    const tick = document.querySelector('.maka-prompt-rail-tick');
-    if (!tick) throw new Error('the prompt rail has no ticks');
-    const box = tick.getBoundingClientRect();
-    const found = document.elementFromPoint(
-      Math.round(box.left + box.width / 2),
-      Math.round(box.top + box.height / 2),
-    );
-    return { insideRail: found?.closest('.maka-prompt-rail') !== null };
-  });
-
-  expect(hit.insideRail).toBe(true);
-});
diff --git a/apps/desktop/e2e/streaming-remount.spec.ts b/apps/desktop/e2e/streaming-remount.spec.ts
index f72efb1f81..d12961ef00 100644
--- a/apps/desktop/e2e/streaming-remount.spec.ts
+++ b/apps/desktop/e2e/streaming-remount.spec.ts
@@ -20,7 +20,6 @@
 import {
   FAKE_HOLD_OPEN_PROMPT,
   FAKE_HOLD_OPEN_REWRITE_PROMPT,
-  FAKE_WAIT_FOR_STEERING_LARGE_RESPONSE_PROMPT,
 } from '@maka/runtime/test-only/fake-backend';
 import type { Locator } from '@playwright/test';
 import {
@@ -175,93 +174,6 @@ test('remounting a live surface leaves accumulated output settled', async ({
     .toBe(true);
 });
 
-test('keeps a completed reply after an interrupted turn and conversation remount', async ({
-  window: page,
-}) => {
-  await page.emulateMedia({ reducedMotion: 'no-preference' });
-  expect(await page.evaluate(() => matchMedia('(prefers-reduced-motion: reduce)').matches)).toBe(false);
-  const composer = page.locator(COMPOSER_INPUT);
-  await composer.fill('temporary conversation');
-  await awaitSendReady(page);
-  await composer.press('Enter');
-  await expect(page.getByRole('log')).toContainText(
-    'Fake backend received: temporary conversation',
-    { timeout: 20_000 },
-  );
-  await expect(page.getByRole('button', { name: '重新生成' })).toHaveCount(1, {
-    timeout: 20_000,
-  });
-  const sidebar = page.getByRole('navigation', { name: '任务列表' });
-  await page.getByRole('button', { name: '展开侧边栏' }).click();
-  await expect(page.locator('[data-agents-page]')).toHaveAttribute(
-    'data-sidebar-state',
-    'expanded',
-  );
-  const temporarySessionId = await sidebar
-    .locator('[data-session-id]:has([aria-current="page"])')
-    .getAttribute('data-session-id');
-  expect(temporarySessionId).toBeTruthy();
-  await composer.fill('draft before starting the interrupted conversation');
-  await sidebar.getByRole('button', { name: '新任务', exact: true }).click();
-  await expect(composer).toHaveText('');
-
-  await composer.fill(FAKE_HOLD_OPEN_PROMPT);
-  await awaitSendReady(page);
-  await composer.press('Enter');
-  await expect(page.locator('.maka-bubble-streaming')).toContainText(
-    'Fake backend waiting',
-    { timeout: 20_000 },
-  );
-  const originalSessionId = await sidebar
-    .locator('[data-session-id]:has([aria-current="page"])')
-    .getAttribute('data-session-id');
-  expect(originalSessionId).toBeTruthy();
-  expect(originalSessionId).not.toBe(temporarySessionId);
-  await page.getByRole('button', { name: '停止' }).click();
-  await expect(page.getByRole('button', { name: '重新生成' })).toHaveCount(1, {
-    timeout: 20_000,
-  });
-  await expect.poll(
-    () => page.evaluate(async (sessionId) => (
-      (await window.maka.sessions.list()).find((session) => session.id === sessionId)
-        ?.runningTurnIds?.length ?? 0
-    ), originalSessionId!),
-    { timeout: 20_000 },
-  ).toBe(0);
-  await composer.fill(FAKE_WAIT_FOR_STEERING_LARGE_RESPONSE_PROMPT);
-  await awaitSendReady(page);
-  await composer.press('Enter');
-  await expect(page.locator('.maka-user-message', {
-    hasText: FAKE_WAIT_FOR_STEERING_LARGE_RESPONSE_PROMPT,
-  })).toBeVisible();
-  await expect(page.getByRole('button', { name: '停止' })).toBeVisible({
-    timeout: 20_000,
-  });
-  const steering = 'use the detailed response';
-  const completedReply = 'Large response complete.';
-  await steerActiveTurn(composer, steering);
-  await expect(page.getByRole('log')).toContainText(completedReply);
-  await expect(page.getByRole('button', { name: '停止' })).toHaveCount(0, {
-    timeout: 20_000,
-  });
-  await expect(page.locator('.maka-bubble-streaming')).toHaveCount(0, {
-    timeout: 20_000,
-  });
-
-  const temporarySessionRow = sessionRow(sidebar, temporarySessionId!);
-  await temporarySessionRow.click();
-  await expect(temporarySessionRow.locator('[aria-current="page"]')).toHaveCount(1, {
-    timeout: 20_000,
-  });
-  await expect(page.getByRole('log')).toContainText('Fake backend received: temporary conversation');
-  const originalSessionRow = sessionRow(sidebar, originalSessionId!);
-  await originalSessionRow.click();
-  await expect(originalSessionRow.locator('[aria-current="page"]')).toHaveCount(1, {
-    timeout: 20_000,
-  });
-  await expect(page.getByRole('log')).toContainText(completedReply);
-});
-
 test('returning to a live conversation settles output accumulated while away', async ({
   window: page,
 }) => {
diff --git a/apps/desktop/e2e/transcript-scroll.spec.ts b/apps/desktop/e2e/transcript-scroll.spec.ts
deleted file mode 100644
index 2a7fa86772..0000000000
--- a/apps/desktop/e2e/transcript-scroll.spec.ts
+++ /dev/null
@@ -1,774 +0,0 @@
-/*
- * Licensed to the Apache Software Foundation (ASF) under one
- * or more contributor license agreements.  See the NOTICE file
- * distributed with this work for additional information
- * regarding copyright ownership.  The ASF licenses this file
- * to you under the Apache License, Version 2.0 (the
- * "License"); you may not use this file except in compliance
- * with the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing,
- * software distributed under the License is distributed on an
- * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
- * KIND, either express or implied.  See the License for the
- * specific language governing permissions and limitations
- * under the License.
- */
-
-import {
-  awaitSendReady,
-  expect,
-  test,
-  COMPOSER_INPUT,
-  ensureSidebarExpanded,
-} from './fixtures';
-import type { Page } from '@playwright/test';
-
-/**
- * Where the transcript is looking, in a real Chromium with a real scroller.
- *
- * Two rounds of this work shipped green and wrong, both times because the
- * instrument could not see the property being claimed: a CLS measurement is
- * blind to scroll position, and a linkedom harness decides the effect ordering
- * its own assertions then confirm. Nothing below reads a ref or a flag — each
- * test states where an element or the viewport ended up, and the app has to put
- * it there.
- *
- * Positions are asserted against an element or against the scroller's own end,
- * never as a pixel delta: a delta is satisfiable by two wrongs (the content
- * grew by as much as the view moved), which is the bug class that produced the
- * `scrollHeight`-difference compensation this replaces.
- */
-
-const SCROLLER = '[data-chat-scroll-container="true"]';
-const REGENERATE = /^重新生成回答/;
-/** Astryx's dock affordance, relabelled by `ChatSurfaceLayout`. */
-const SCROLL_TO_BOTTOM = /^滚动主对话到底部$/;
-
-/** Sixty lines: more than one viewport once the fake backend echoes it back. */
-const LONG_PROMPT = Array.from(
-  { length: 60 },
-  (_, index) => `第 ${index} 行：这一段用来把转录推过滚动视口的高度。`,
-).join('\n');
-
-function distanceToTail(page: Page): Promise<number> {
-  return scrollMetrics(page).then((metrics) => metrics.distance);
-}
-
-/**
- * The distance plus the three numbers it came from. A failure that reports only
- * the distance cannot say whether the transcript grew past the reader or the
- * viewport shrank under them, and those have different causes.
- */
-function scrollMetrics(page: Page): Promise<{
-  distance: number;
-  scrollTop: number;
-  scrollHeight: number;
-  clientHeight: number;
-}> {
-  return page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    return {
-      distance: Math.round(root.scrollHeight - root.scrollTop - root.clientHeight),
-      scrollTop: Math.round(root.scrollTop),
-      scrollHeight: root.scrollHeight,
-      clientHeight: root.clientHeight,
-    };
-  }, SCROLLER);
-}
-
-/**
- * Whether the dock affordance is actually offered. It is always in the DOM —
- * Astryx toggles opacity and pointer-events — so presence proves nothing and
- * `toBeVisible` passes on the transparent one.
- */
-function scrollButtonOffered(page: Page): Promise<boolean> {
-  return page.evaluate((names) => {
-    const button = [...document.querySelectorAll('button')].find(
-      (candidate) => names.includes(candidate.getAttribute('aria-label') ?? '')
-        || names.includes(candidate.textContent?.trim() ?? ''),
-    );
-    if (!button) throw new Error(`the "${names.join('" / "')}" affordance is missing`);
-    const style = getComputedStyle(button);
-    return style.pointerEvents !== 'none' && Number(style.opacity) > 0.5;
-  }, ['滚动主对话到底部', 'Scroll main conversation to bottom']);
-}
-
-function turnTop(page: Page, turnId: string): Promise<number> {
-  return page.evaluate((id) => {
-    const turn = document.querySelector(`[data-turn-id="${CSS.escape(id)}"]`);
-    if (!turn) throw new Error(`turn ${id} is not mounted`);
-    return Math.round(turn.getBoundingClientRect().top);
-  }, turnId);
-}
-
-function turnOffsetFromScroller(page: Page, turnId: string): Promise<number> {
-  return page.evaluate(([selector, id]) => {
-    const root = document.querySelector(selector);
-    const turn = document.querySelector(`[data-turn-id="${CSS.escape(id as string)}"]`);
-    if (!root || !turn) return Number.POSITIVE_INFINITY;
-    return Math.round(turn.getBoundingClientRect().top - root.getBoundingClientRect().top);
-  }, [SCROLLER, turnId] as const);
-}
-
-function waitForStableTurnAtScrollerStart(page: Page, turnId: string): Promise<void> {
-  return page.evaluate(([selector, id]) => new Promise<void>((resolve, reject) => {
-    let previousTop = Number.NaN;
-    let previousHeight = Number.NaN;
-    let stableFrames = 0;
-    const timeout = window.setTimeout(
-      () => reject(new Error(`Turn ${id} did not settle at the scroller start`)),
-      10_000,
-    );
-    const measure = (): void => {
-      const root = document.querySelector<HTMLElement>(selector);
-      const turn = root?.querySelector<HTMLElement>(`[data-turn-id="${CSS.escape(id)}"]`);
-      if (root && turn) {
-        const offset = turn.getBoundingClientRect().top - root.getBoundingClientRect().top;
-        stableFrames = Math.abs(offset) <= 4
-            && root.scrollTop === previousTop
-            && root.scrollHeight === previousHeight
-          ? stableFrames + 1
-          : 0;
-        previousTop = root.scrollTop;
-        previousHeight = root.scrollHeight;
-        if (stableFrames >= 6) {
-          window.clearTimeout(timeout);
-          resolve();
-          return;
-        }
-      }
-      window.requestAnimationFrame(measure);
-    };
-    measure();
-  }), [SCROLLER, turnId]);
-}
-
-/**
- * Sample the tail through the frames a growing transcript produces.
- *
- * Read at the start of each frame, which is one frame behind the pin: the
- * content commits, the next frame's layout delivers the resize, and the write
- * lands before that frame paints. So the view can only ever be behind by what
- * arrived since the last delivery — never more, and never cumulatively. That is
- * what `worstLag` against `worstFrameGrowth` states, and it is a property no
- * fixed pixel budget can express: a transcript that stopped following instead
- * falls behind by the whole of `grewBy`.
- */
-function measureTailLag(page: Page, frames: number): Promise<{
-  worstLag: number;
-  worstFrameGrowth: number;
-  grewBy: number;
-  viewportHeight: number;
-}> {
-  return page.evaluate(([selector, frameCount]) => new Promise<{
-    worstLag: number;
-    worstFrameGrowth: number;
-    grewBy: number;
-    viewportHeight: number;
-  }>((resolve) => {
-    const root = document.querySelector(selector as string);
-    if (!root) throw new Error('the chat scroll container is missing');
-    const startedAt = root.scrollHeight;
-    let previousScrollHeight = startedAt;
-    let worstLag = 0;
-    let worstFrameGrowth = 0;
-    let left = frameCount as number;
-    const tick = (): void => {
-      const settledTail = previousScrollHeight - root.clientHeight;
-      worstLag = Math.max(worstLag, Math.abs(root.scrollTop - settledTail));
-      worstFrameGrowth = Math.max(worstFrameGrowth, root.scrollHeight - previousScrollHeight);
-      previousScrollHeight = root.scrollHeight;
-      // Stops on the content, not on a frame count: when the answer starts
-      // arriving is the backend's business, and a fixed window can expire
-      // before it does.
-      const enough = root.scrollHeight - startedAt > root.clientHeight;
-      if (enough || --left <= 0) {
-        resolve({
-          worstLag: Math.round(worstLag),
-          worstFrameGrowth: Math.round(worstFrameGrowth),
-          grewBy: Math.round(root.scrollHeight - startedAt),
-          viewportHeight: root.clientHeight,
-        });
-      } else requestAnimationFrame(tick);
-    };
-    requestAnimationFrame(tick);
-  }), [SCROLLER, frames] as const);
-}
-
-async function sendPrompt(page: Page, text: string): Promise<void> {
-  const composer = page.locator(COMPOSER_INPUT);
-  await composer.fill(text);
-  // Switching Session or model restarts asynchronous send admission.
-  await awaitSendReady(page);
-  await composer.press('Enter');
-}
-
-/** Answered turns, so a second send can be waited for without a stale match. */
-function answeredTurns(page: Page) {
-  return page.getByRole('button', { name: REGENERATE });
-}
-
-async function scrollTranscriptTo(page: Page, top: number): Promise<void> {
-  await page.evaluate(([selector, position]) => {
-    const root = document.querySelector(selector as string);
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.scrollTop = position as number;
-  }, [SCROLLER, top] as const);
-  await waitForPaintedFrames(page);
-}
-
-async function waitForPaintedFrames(page: Page, count = 3): Promise<void> {
-  await page.evaluate((frames) => new Promise<void>((resolve) => {
-    const tick = (left: number) => {
-      if (left <= 0) {
-        resolve();
-        return;
-      }
-      requestAnimationFrame(() => tick(left - 1));
-    };
-    tick(frames);
-  }), count);
-}
-
-test('a streaming answer keeps the viewport at the tail', async ({ window: page }) => {
-  // A full fake-backend turn, streamed nine characters at a time.
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await sendPrompt(page, LONG_PROMPT);
-
-  // Measured through the stream, not only at the end: the failure this guards
-  // against is the tail slipping away *while* content arrives, which a single
-  // reading afterwards cannot tell apart from a view dragged back at the last
-  // delta.
-  const lag = await measureTailLag(page, 1_200);
-  await expect(answeredTurns(page)).toHaveCount(1, { timeout: 30_000 });
-
-  // The samples have to have covered more than a viewport of real growth, or
-  // every reading above is a stationary transcript and proves nothing.
-  expect(lag.grewBy).toBeGreaterThan(lag.viewportHeight);
-  expect(lag.worstLag).toBeLessThanOrEqual(lag.worstFrameGrowth + 8);
-  const settled = await scrollMetrics(page);
-  expect(settled.distance, JSON.stringify(settled)).toBeLessThanOrEqual(4);
-  expect(await scrollButtonOffered(page)).toBe(false);
-});
-
-test('switching Sessions restores a Turn anchor while a tail Session follows background growth', async ({
-  promptRailWindow: page,
-}) => {
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await ensureSidebarExpanded(page);
-  const rows = page.locator('.maka-session-row');
-  const selected = rows.locator('button.astryx-side-nav-item.selected');
-  const readingSessionId = await selected.evaluate(
-    (button) => button.closest('.maka-session-row')?.getAttribute('data-session-id'),
-  );
-  if (!readingSessionId) throw new Error('the prompt-rail Session is not selected');
-  const tailSessionId = await rows.evaluateAll(
-    (items, active) => items
-      .map((row) => row.getAttribute('data-session-id'))
-      .find((sessionId) => sessionId !== active) ?? null,
-    readingSessionId,
-  );
-  if (!tailSessionId) throw new Error('the fixture has no tail-intent Session');
-  const rowButton = (sessionId: string) => page.locator(
-    `.maka-session-row[data-session-id=${JSON.stringify(sessionId)}] button`,
-  ).first();
-
-  // Move the active bounded range away from the latest window, then establish
-  // a reading position through the real scroll event path. Reopening the
-  // Session now has to use the saved sequence before the Turn can exist.
-  await page.locator('.maka-prompt-rail-tick').first().click({ force: true });
-  const readingTurnId = 'turn-prompt-rail-1';
-  await expect(page.locator(`[data-turn-id="${readingTurnId}"]`)).toHaveCount(1, {
-    timeout: 20_000,
-  });
-  await expect.poll(
-    async () => Math.abs(await turnOffsetFromScroller(page, readingTurnId)),
-    { message: 'the unloaded prompt reaches the scroller start' },
-  ).toBeLessThanOrEqual(24);
-  // The prompt rail holds its target through late content measurement. Six
-  // unchanged painted frames exceed its own quiet-frame handoff, so switching
-  // after this point cannot carry that release into the next Session. Observe
-  // transcript geometry directly: the Astryx dock can be briefly unmounted on
-  // a loaded Xvfb worker even though the reading position is already stable.
-  await waitForStableTurnAtScrollerStart(page, readingTurnId);
-  expect(await distanceToTail(page)).toBeGreaterThan(100);
-
-  await rowButton(tailSessionId).click();
-  await expect(rowButton(tailSessionId)).toHaveClass(/selected/);
-  await waitForPaintedFrames(page, 6);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-  // The fixture Session predates connection identities. Choosing any current
-  // model upgrades it onto the E2E Runtime Host before this test starts a Turn.
-  const modelSwitcher = page.locator('.maka-model-switcher-trigger');
-  await modelSwitcher.click();
-  await page.getByRole('menuitemradio', { name: 'glm-4.5', exact: true }).click();
-  await expect(modelSwitcher).toContainText('glm-4.5');
-
-  await page.evaluate((sessionId) => {
-    const state = { complete: false, unsubscribe: () => undefined };
-    state.unsubscribe = window.maka.sessions.subscribeEvents(sessionId, (event) => {
-      if (event.type !== 'complete') return;
-      state.complete = true;
-      state.unsubscribe();
-    });
-    (window as typeof window & { __makaBackgroundTailProbe?: typeof state })
-      .__makaBackgroundTailProbe = state;
-  }, tailSessionId);
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(page.locator('.maka-user-message', { hasText: '第 1 行' })).toBeVisible({
-    timeout: 20_000,
-  });
-
-  // The transcript collapses before each async replacement. This round trip
-  // therefore exercises the production ordering that made a saved scrollTop
-  // become zero, not merely a pre-filled test tree.
-  await rowButton(readingSessionId).click();
-  await expect.poll(
-    async () => Math.abs(await turnOffsetFromScroller(page, readingTurnId)),
-    { timeout: 20_000, message: 'the saved reading Turn returns to the scroller start' },
-  ).toBeLessThanOrEqual(4);
-  expect(await scrollButtonOffered(page)).toBe(true);
-
-  await expect.poll(() => page.evaluate(() => (
-    window as typeof window & {
-      __makaBackgroundTailProbe?: { complete: boolean };
-    }
-  ).__makaBackgroundTailProbe?.complete === true), { timeout: 30_000 }).toBe(true);
-  await rowButton(tailSessionId).click();
-  await expect(rowButton(tailSessionId)).toHaveClass(/selected/);
-  await waitForPaintedFrames(page, 6);
-  const tail = await scrollMetrics(page);
-  expect(tail.distance, JSON.stringify(tail)).toBeLessThanOrEqual(4);
-  expect(await scrollButtonOffered(page)).toBe(false);
-});
-
-/**
- * The turn wrappers are not the transcript. It also renders the optimistic user
- * message, the no-tail live fallback and orphaned conversation items outside
- * them, so a growth signal that watches turns has a blind spot the size of
- * whatever else gets rendered next.
- *
- * Grown here rather than by sending a Follow Up: whether the optimistic message
- * is ever on screen is the host's timing, and it was measured both appearing
- * and being overtaken by its own answer within the same fixture. What is under
- * test is not that message — it is that `scrollHeight` growing anywhere is
- * enough, which is a property of the scroller and needs no help from the
- * transcript to state.
- */
-test('content that grows outside the turn wrappers is followed too', async ({
-  window: page,
-}) => {
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(1, { timeout: 30_000 });
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-
-  const outsideTurnWrapper = await page.evaluate(() => {
-    const list = document.querySelector('.maka-chat-message-list');
-    if (!list) throw new Error('the transcript content box is missing');
-    const grown = document.createElement('div');
-    grown.dataset.outsideTurnGrowth = 'true';
-    grown.style.height = '600px';
-    list.append(grown);
-    return grown.closest('[data-transcript-turn-id]') === null;
-  });
-  await waitForPaintedFrames(page);
-
-  // Outside a wrapper is what makes this the uncovered path: growth inside one
-  // is what every other test in this file already exercises.
-  expect(outsideTurnWrapper, 'the injected box landed inside a turn wrapper').toBe(true);
-  const settled = await scrollMetrics(page);
-  expect(settled.distance, JSON.stringify(settled)).toBeLessThanOrEqual(4);
-});
-
-test('content that arrives after the reader scrolls up does not pull them back', async ({
-  window: page,
-}) => {
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(1, { timeout: 30_000 });
-
-  const transcript = page.locator('.maka-chat-message-list');
-  await transcript.hover();
-  await page.mouse.wheel(0, -500);
-  await waitForPaintedFrames(page);
-  const before = await distanceToTail(page);
-  expect(before).toBeGreaterThan(100);
-  expect(await scrollButtonOffered(page)).toBe(true);
-
-  const anchorTurnId = await page.evaluate(() => {
-    const turn = document.querySelector<HTMLElement>('[data-turn-id]');
-    const turnId = turn?.dataset.turnId;
-    if (!turnId) throw new Error('the transcript has no mounted turn');
-    return turnId;
-  });
-  const anchorTop = await turnTop(page, anchorTurnId);
-
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(2, { timeout: 30_000 });
-  await waitForPaintedFrames(page);
-
-  // The turn the reader was on is still where it was. Everything that arrived,
-  // arrived below them.
-  expect(Math.abs((await turnTop(page, anchorTurnId)) - anchorTop)).toBeLessThanOrEqual(4);
-  expect(await distanceToTail(page)).toBeGreaterThan(before);
-});
-
-test('a gesture a nested scroller consumed does not release the tail', async ({
-  window: page,
-}) => {
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(1, { timeout: 30_000 });
-  // The turn's arrival and the tail-follow write are two steps, so one sample
-  // races the follow on a loaded runner. Poll until the reader has provably
-  // been carried back to the tail.
-  await expect.poll(async () => (await scrollMetrics(page)).distance, {
-    message: 'the transcript follows the landed answer to the tail',
-  }).toBeLessThanOrEqual(4);
-
-  // A real scroller inside the transcript, standing in for a tool-output box
-  // (`.maka-tool-output-body`, `max-height: 256px; overflow-y: auto`) or a pty
-  // terminal. Built here rather than fixtured because what is under test is
-  // Chromium's scroll chain, which does not care where the element came from,
-  // and no fixture reliably produces an output tall enough to overflow.
-  const nested = await page.evaluate(() => {
-    const turns = document.querySelectorAll<HTMLElement>('[data-turn-id]');
-    const turn = turns[turns.length - 1];
-    if (!turn) throw new Error('the transcript has no mounted turn');
-    const box = document.createElement('div');
-    box.dataset.nestedScroller = 'true';
-    box.style.cssText = 'max-height:120px;overflow-y:auto';
-    const filler = document.createElement('div');
-    filler.style.height = '2000px';
-    box.append(filler);
-    turn.append(box);
-    // Away from both ends, so scrolling up inside it never reaches a boundary
-    // and never chains to the transcript.
-    box.scrollTop = 600;
-    return box.scrollTop;
-  });
-
-  // Appending is growth like any other, so the pin brings the new box into
-  // view — which also keeps Playwright's hover from scrolling to reach it.
-  await waitForPaintedFrames(page);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-
-  // The real input pipeline, over the nested element: the gesture crosses the
-  // transcript on its way up the tree, the nested element consumes it, and the
-  // transcript never moves — so no `scroll` follows. A tail-follow that watches
-  // gestures reads this as the reader leaving; one that watches position cannot
-  // see it at all. Astryx's stock predicate is the former, and its
-  // `animatingRef` was measured sitting at `true` on a resting transcript, so
-  // an upward wheel here released the tail with nothing having scrolled.
-  await page.locator('[data-nested-scroller="true"]').hover();
-  await page.mouse.wheel(0, -400);
-  await waitForPaintedFrames(page);
-  const nestedAfter = await page.evaluate(
-    () => document.querySelector<HTMLElement>('[data-nested-scroller="true"]')?.scrollTop ?? -1,
-  );
-  // The nested box moved, which is what makes this a gesture the transcript
-  // never saw. Without this the test would pass on a wheel that did nothing.
-  expect(nestedAfter).toBeLessThan(nested);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-
-  // The touch equivalent, which no synthetic-free path can produce here.
-  await page.evaluate(() => {
-    const target = document.querySelector('[data-turn-id]');
-    if (!target) throw new Error('the transcript has no mounted turn');
-    target.dispatchEvent(new Event('touchmove', { bubbles: true }));
-  });
-  await waitForPaintedFrames(page);
-
-  // Following is unharmed: a whole further answer lands and the tail is still
-  // under the reader. A release would have left them a screen and a half up,
-  // with no gesture of their own to explain it.
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(2, { timeout: 30_000 });
-  await waitForPaintedFrames(page);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-  expect(await scrollButtonOffered(page)).toBe(false);
-});
-
-test('a nested scroller near the history boundary does not request an earlier range', async ({
-  promptRailWindow: page,
-}) => {
-  await page.setViewportSize({ width: 900, height: 1500 });
-  await waitForPaintedFrames(page, 6);
-  // The fixture is ready when the transcript exists, before its initial tail
-  // positioning necessarily completes. Poll one geometry sample so the pin has
-  // provably settled inside the load band and at the tail before the nested
-  // scroller exercises it.
-  await expect.poll(async () => {
-    const metrics = await scrollMetrics(page);
-    return {
-      insideLoadBand: metrics.scrollTop <= Math.max(640, metrics.clientHeight * 2),
-      settledAtTail: metrics.distance <= 4,
-      metrics,
-    };
-  }, {
-    message: 'the initial transcript tail positioning settles',
-  }).toMatchObject({
-    insideLoadBand: true,
-    settledAtTail: true,
-  });
-
-  const nestedBefore = await page.evaluate((selector) => {
-    const root = document.querySelector<HTMLElement>(selector);
-    const list = root?.querySelector<HTMLElement>('.maka-chat-message-list');
-    if (!root || !list) throw new Error('the active transcript range is missing');
-    const box = document.createElement('div');
-    box.dataset.nestedHistoryScroller = 'true';
-    box.style.cssText = [
-      'position:fixed',
-      'top:160px',
-      'left:160px',
-      'width:240px',
-      'height:120px',
-      'overflow-y:auto',
-      'z-index:9999',
-    ].join(';');
-    const filler = document.createElement('div');
-    filler.style.height = '2000px';
-    box.append(filler);
-    // A Turn uses `content-visibility:auto`, whose paint containment prevents
-    // a fixed descendant from reliably winning hit testing over sibling Turns
-    // on Linux/Xvfb. Keep the fixture inside the transcript event path without
-    // putting it inside the product containment boundary being tested.
-    list.append(box);
-    box.scrollTop = 600;
-    return box.scrollTop;
-  }, SCROLLER);
-
-  const nested = page.locator('[data-nested-history-scroller="true"]');
-  const box = await nested.boundingBox();
-  if (!box) throw new Error('the nested history scroller is not rendered');
-  const point = { x: box.x + box.width / 2, y: box.y + box.height / 2 };
-  expect(await page.evaluate(({ x, y }) =>
-    document.elementFromPoint(x, y)?.closest('[data-nested-history-scroller="true"]') !== null,
-  point)).toBe(true);
-  await page.mouse.move(point.x, point.y);
-  await page.mouse.wheel(0, -400);
-  await waitForPaintedFrames(page);
-
-  const nestedAfter = await page.evaluate(() =>
-    document.querySelector<HTMLElement>('[data-nested-history-scroller="true"]')?.scrollTop ?? -1,
-  );
-  expect(nestedAfter).toBeLessThan(nestedBefore);
-  await page.evaluate(() => {
-    const list = document.querySelector('.maka-chat-message-list');
-    if (!list) throw new Error('the transcript content box is missing');
-    const grown = document.createElement('div');
-    grown.style.height = '600px';
-    list.append(grown);
-  });
-  await waitForPaintedFrames(page, 6);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-});
-
-test('the dock affordance returns the reader to the tail', async ({ window: page }) => {
-  test.slow();
-  await page.setViewportSize({ width: 900, height: 700 });
-  await sendPrompt(page, LONG_PROMPT);
-  await expect(answeredTurns(page)).toHaveCount(1, { timeout: 30_000 });
-
-  await scrollTranscriptTo(page, 0);
-  // Offered at all is the assertion: with Astryx's scroll layer off, its
-  // `isScrolledUp` never updates again, so the stock button would stay
-  // transparent forever. This one reads Maka's pin.
-  expect(await scrollButtonOffered(page)).toBe(true);
-
-  await page.getByRole('button', { name: SCROLL_TO_BOTTOM }).click();
-  await waitForPaintedFrames(page);
-  expect(await distanceToTail(page)).toBeLessThanOrEqual(4);
-  expect(await scrollButtonOffered(page)).toBe(false);
-});
-
-test('earlier history lands above the turn the reader is on', async ({
-  promptRailWindow: page,
-}) => {
-  const firstLoadedTurn = () => page
-    .locator('[data-transcript-turn-id]')
-    .first()
-    .getAttribute('data-transcript-turn-id');
-  const firstBefore = await firstLoadedTurn();
-
-  // Just short of the band that asks for more, so the active range has painted
-  // turns around the reader before the load starts. Landing straight on zero
-  // leaves no visible turn above the load boundary to identify as the anchor.
-  await page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.scrollTop = Math.max(640, root.clientHeight * 2) + 400;
-  }, SCROLLER);
-  await waitForPaintedFrames(page, 6);
-
-  // The move that asks for earlier history, and the reading of where the
-  // reader is, in one task. Keep the reader near the active range's head: an
-  // anchor near its tail can already have a complete bounded range around it,
-  // so a valid load has no reason to move the first resident Turn.
-  const anchor = await page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.scrollTop = Math.min(300, root.scrollHeight - root.clientHeight);
-    const rootTop = root.getBoundingClientRect().top;
-    const turn = [...root.querySelectorAll<HTMLElement>('[data-turn-id]')].find(
-      (candidate) => candidate.getBoundingClientRect().bottom > rootTop,
-    );
-    const turnId = turn?.dataset.turnId;
-    if (!turn || !turnId) throw new Error('no turn is on screen');
-    const anchor = { turnId, top: Math.round(turn.getBoundingClientRect().top) };
-    root.dispatchEvent(new WheelEvent('wheel', { deltaY: -120, bubbles: true }));
-    return anchor;
-  }, SCROLLER);
-
-  await expect.poll(firstLoadedTurn, { timeout: 20_000 }).not.toBe(firstBefore);
-  await waitForPaintedFrames(page);
-
-  // The turns that arrived went above the reader, and the reader did not go
-  // with them. Asserting the element rather than a `scrollTop` delta is the
-  // point: a compensation computed from `scrollHeight` satisfies the delta
-  // while putting the reader somewhere else entirely.
-  await expect.poll(
-    async () => Math.abs((await turnTop(page, anchor.turnId)) - anchor.top),
-  ).toBeLessThanOrEqual(4);
-});
-
-test('history asked for at the very top of the scroller still lands above the reader', async ({
-  promptRailWindow: page,
-}) => {
-  const firstLoadedTurn = () => page
-    .locator('[data-transcript-turn-id]')
-    .first()
-    .getAttribute('data-transcript-turn-id');
-  const firstBefore = await firstLoadedTurn();
-
-  // The fixture is ready when the transcript exists, before its initial tail
-  // positioning necessarily completes. Writing zero while it is still at zero
-  // is a no-op, so no reader scroll event asks for earlier history. Require one
-  // geometry sample to prove both that the initial pin moved and where it
-  // landed before exercising the real move to the top.
-  await expect.poll(async () => {
-    const metrics = await scrollMetrics(page);
-    return {
-      positionedAwayFromStart: metrics.scrollTop > 0,
-      settledAtTail: metrics.distance <= 4,
-      metrics,
-    };
-  }, {
-    message: 'the initial transcript tail positioning settles',
-  }).toMatchObject({
-    positionedAwayFromStart: true,
-    settledAtTail: true,
-  });
-
-  // The one position where the browser declines to anchor, and the one the
-  // wheel-to-load path puts the reader in.
-  await page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.scrollTop = 0;
-    root.dispatchEvent(new WheelEvent('wheel', { deltaY: -120, bubbles: true }));
-  }, SCROLLER);
-
-  await expect.poll(firstLoadedTurn, { timeout: 20_000 }).not.toBe(firstBefore);
-  await waitForPaintedFrames(page);
-
-  // Anchoring resumes at an offset of one pixel, so the offset itself is the
-  // evidence: left at zero the browser holds the scroller at the top and every
-  // turn that arrives pushes the reader's content down the viewport instead.
-  const offset = await page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    return root.scrollTop;
-  }, SCROLLER);
-  expect(offset).toBeGreaterThanOrEqual(1);
-});
-
-/**
- * A transcript shorter than about three viewports has its tail inside the band
- * that asks for earlier history, so "near the start" cannot mean the reader
- * wants it.
- *
- * The other half of that rule — a wheel the scroller cannot act on releases the
- * pin, because it is the reader asking for what is above them — has no assertion
- * here, and not for want of trying. Its only observable consequence is that a
- * later arrival does not take the reader back down, and in this fixture the
- * reader who asks is already at the tail: anchoring holds them at the same
- * distance from it, the session takes no new turns, and a viewport change moves
- * them the same way pinned or not. An assertion that passes either way is worse
- * than none. `transcript-scroll-authority.test.ts` covers the state machine it
- * turns on.
- */
-test('following the tail does not ask for the history above it', async ({
-  promptRailWindow: page,
-}) => {
-  const firstLoadedTurn = () => page
-    .locator('[data-transcript-turn-id]')
-    .first()
-    .getAttribute('data-transcript-turn-id');
-  const firstBefore = await firstLoadedTurn();
-
-  // Tall enough that the tail sits inside `max(640, clientHeight * 2)`. The
-  // resize itself is a growth signal, so the pin writes the tail and that write
-  // dispatches the scroll event this test is about.
-  await page.setViewportSize({ width: 900, height: 1500 });
-  await waitForPaintedFrames(page, 6);
-
-  // Same as above: the fixture being ready does not mean the initial tail
-  // positioning has completed. Poll until the pin has provably settled at the
-  // tail and inside the load band this test's history claim rests on.
-  await expect.poll(async () => {
-    const settled = await scrollMetrics(page);
-    return {
-      insideLoadBand: settled.scrollTop <= Math.max(640, settled.clientHeight * 2),
-      settledAtTail: settled.distance <= 4,
-      settled,
-    };
-  }, {
-    message: 'the initial transcript tail positioning settles',
-  }).toMatchObject({
-    insideLoadBand: true,
-    settledAtTail: true,
-  });
-
-  // Nothing arrived that the reader did not ask for.
-  await waitForPaintedFrames(page, 12);
-  expect(await firstLoadedTurn()).toBe(firstBefore);
-});
-
-test('a wheel a short scroller cannot act on still asks for history', async ({
-  promptRailWindow: page,
-}) => {
-  const firstLoadedTurn = () => page
-    .locator('[data-transcript-turn-id]')
-    .first()
-    .getAttribute('data-transcript-turn-id');
-  const firstBefore = await firstLoadedTurn();
-
-  await page.setViewportSize({ width: 900, height: 4000 });
-  await waitForPaintedFrames(page, 6);
-  const asked = await scrollMetrics(page);
-  expect(asked.distance, JSON.stringify(asked)).toBeLessThanOrEqual(4);
-
-  // Dispatched rather than driven, and that is the point: the case is a wheel
-  // the scroller cannot act on — already at zero, or too short to move — where
-  // no scroll follows and the authority never learns the reader asked. A real
-  // `mouse.wheel` would scroll, and the scroll alone would carry the request.
-  await page.evaluate((selector) => {
-    const root = document.querySelector(selector);
-    if (!root) throw new Error('the chat scroll container is missing');
-    root.dispatchEvent(new WheelEvent('wheel', { deltaY: -120, bubbles: true }));
-  }, SCROLLER);
-
-  await expect.poll(firstLoadedTurn, { timeout: 20_000 }).not.toBe(firstBefore);
-});
diff --git a/apps/desktop/src/main/e2e-fixture/scenarios-chat.ts b/apps/desktop/src/main/e2e-fixture/scenarios-chat.ts
index 1ff6f54af6..fb26506f70 100644
--- a/apps/desktop/src/main/e2e-fixture/scenarios-chat.ts
+++ b/apps/desktop/src/main/e2e-fixture/scenarios-chat.ts
@@ -133,8 +133,8 @@ export function promptRailSession(now: number): SessionHeader {
 
 /**
  * A plain multi-prompt conversation: no tools, no thinking, no usage rows.
- * `prompt-rail.spec.ts` measures the rail against this, so every turn is just
- * a prompt and a reply long enough to push the transcript past the scrollport.
+ * The transcript perf suite measures against this, so every turn is just a
+ * prompt and a reply long enough to push the transcript past the scrollport.
  */
 export function promptRailMessages(now: number): StoredMessage[] {
   const messages: StoredMessage[] = [];
diff --git a/apps/desktop/src/renderer/scroll-motion-policy.ts b/apps/desktop/src/renderer/scroll-motion-policy.ts
index 52a50e0c4c..74cf336533 100644
--- a/apps/desktop/src/renderer/scroll-motion-policy.ts
+++ b/apps/desktop/src/renderer/scroll-motion-policy.ts
@@ -53,10 +53,9 @@ export interface ScrollMotionPolicyInputs {
    *
    * Collapsing motion for every capture is right for a screenshot and wrong
    * for a test about scrolling: a scroll that finishes in one frame cannot
-   * collide with anything, so the fixture suite had no way to exercise the
-   * production smooth path at all (`prompt-rail.spec.ts` needs it — Astryx's
-   * auto-follow lock only contends with a scroll still in flight). This lets
-   * one fixture opt back in without loosening the default for the rest.
+   * collide with anything, and Astryx's auto-follow lock only contends with a
+   * scroll still in flight. This lets one fixture opt back in without
+   * loosening the default for the rest.
    *
    * Deliberately below the reduced-motion triggers: a fixture may ask for
    * motion the capture would otherwise skip, but nothing may override a
diff --git a/packages/ui/src/__tests__/transcript-scroll-authority.test.ts b/packages/ui/src/__tests__/transcript-scroll-authority.test.ts
index aaf66433a9..9901780cb0 100644
--- a/packages/ui/src/__tests__/transcript-scroll-authority.test.ts
+++ b/packages/ui/src/__tests__/transcript-scroll-authority.test.ts
@@ -19,9 +19,9 @@
 
 /**
  * The state machine only. Whether the reader ends up looking at the right
- * pixels is `apps/desktop/e2e/transcript-scroll.spec.ts`, in a real Chromium
- * with a real scroller — a harness that fakes layout can only report the
- * ordering the harness itself chose.
+ * pixels needs a real layout engine and currently has no test at all — a
+ * harness that fakes layout can only report the ordering the harness itself
+ * chose, so do not add that claim here.
  *
  * What is worth asserting here is the one property the whole design rests on:
  * a scroll event that this authority did not cause is the reader, exactly, with