diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index f96577d1e8..8620b3d9d4 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -159,14 +159,14 @@ jobs:
       # The app's real-browser tests, here because this job has the browser: a running step's words
       # under reduced motion, where onboarding's Back lands beside the Mac window's buttons, the name
       # step's orb drawn whole under the step dashes, and the New Bot sheet's first four frameworks
-      # clearing its footer in an 800px window, which only a browser's layout resolves. The root
-      # playwright-core is the same version as
+      # clearing its footer in an 800px window, and a conversation's rail of turns clear of the Bot's
+      # text, which only a browser's layout resolves. The root playwright-core is the same version as
       # agent-computer's playwright, so it finds the Chromium installed above. The onboarding frame
       # reads the generated app config, which `bun test` alone doesn't write (the test script's
       # pretest does).
       - run: |
           bun run generate:app-config
-          bun test app/tests/tool-line-reduced-motion.test.tsx app/tests/onboarding-window-buttons.test.tsx app/tests/onboarding-orb-room.test.tsx app/tests/new-bot-sheet-fit.test.tsx
+          bun test app/tests/tool-line-reduced-motion.test.tsx app/tests/onboarding-window-buttons.test.tsx app/tests/onboarding-orb-room.test.tsx app/tests/new-bot-sheet-fit.test.tsx app/tests/transcript-rail-clearance.test.tsx
         env:
           OPENBOT_APP_BROWSER: '1'
       # Headed is the default for hosted computers, so it is tested as one: the computer starting its
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 58c3255a04..b1ca1e95f3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -171,6 +171,8 @@ deployment:
   host-grant-15407-… for shopper-bot".
 - An opened "Looked for a tool" step lists the tools the Bot found by name ("Send email on Gmail"),
   where it showed their ids and the descriptions the search returned to the Bot.
+- The marks for each turn on the left of a conversation no longer sit on the first letters of a
+  Bot's replies. They show only where the window leaves room for them beside the messages.
 
 ### Personal edition
 
diff --git a/app/src/components/channels/transcript-rail.tsx b/app/src/components/channels/transcript-rail.tsx
index 3c8b82b3fb..60c9b1f004 100644
--- a/app/src/components/channels/transcript-rail.tsx
+++ b/app/src/components/channels/transcript-rail.tsx
@@ -40,9 +40,9 @@ export function sameRail(a: RailProps, b: RailProps): boolean {
  * Hovering or focusing a mark previews its turn — what the person sent, and the start of the
  * reply — and choosing it goes there.
  *
- * Only where the margin is wide enough to hold it (`@3xl` of the scroller: the transcript's
- * `max-w-2xl` column and a gutter either side), and only once there is more than one turn to move
- * between.
+ * Only where the margin is wide enough to hold it clear of the messages (`@4xl` of the scroller,
+ * 896px: the transcript's 768px `max-w-3xl` column, and 64px either side for the marks and a gap
+ * after them), and only once there is more than one turn to move between.
  */
 export const TranscriptRail = memo(function TranscriptRail({
   turns,
@@ -64,7 +64,7 @@ export const TranscriptRail = memo(function TranscriptRail({
   return (
     <nav
       aria-label="Turns"
-      className="pointer-events-none absolute inset-y-0 left-2 z-10 hidden items-center @3xl:flex"
+      className="pointer-events-none absolute inset-y-0 left-2 z-10 hidden items-center @4xl:flex"
     >
       <ol
         className="pointer-events-auto flex max-h-[min(60vh,32rem)] flex-col overflow-y-auto py-2 [scrollbar-width:none]"
diff --git a/app/tests/transcript-rail-clearance.fixture.tsx b/app/tests/transcript-rail-clearance.fixture.tsx
new file mode 100644
index 0000000000..cce3c07fd8
--- /dev/null
+++ b/app/tests/transcript-rail-clearance.fixture.tsx
@@ -0,0 +1,52 @@
+import type { Message } from "@ag-ui/core";
+import { CopilotKitProvider } from "@copilotkit/react-core/v2";
+import { QueryClient, QueryClientProvider } from "@tanstack/react-query";
+import { createRoot } from "react-dom/client";
+import { ChatTranscript } from "@/components/channels/chat-transcript";
+import { TooltipProvider } from "@/components/ui/tooltip";
+
+/**
+ * A conversation of several turns, the transcript filling the window, as a page of its own for
+ * transcript-rail-clearance.test.tsx to bundle and load in Chromium. Enough turns for the rail to
+ * draw; the Bot's replies are prose, a list and a code block, so their text and their boxes start
+ * at the column's left edge.
+ */
+const REPLIES = [
+  "Here is what changed in the quarterly numbers since last week, and where the gap came from.",
+  "Three things stand out:\n\n- Signups rose in the second half\n- Churn held flat\n- Expansion revenue doubled",
+  "The query I ran:\n\n```sql\nselect region, sum(amount) from orders group by region;\n```",
+  "Shall I draft the summary for the team channel, or send it to you first?",
+];
+const messages: Message[] = REPLIES.flatMap((reply, index) => [
+  {
+    id: `u${index}`,
+    role: "user" as const,
+    content: `Question number ${index + 1} about the numbers`,
+  },
+  { id: `a${index}`, role: "assistant" as const, content: reply },
+]);
+
+const queryClient = new QueryClient({
+  defaultOptions: { queries: { retry: false } },
+});
+
+const root = document.getElementById("root");
+if (root) {
+  createRoot(root).render(
+    <QueryClientProvider client={queryClient}>
+      <CopilotKitProvider runtimeUrl="/api/copilotkit">
+        <TooltipProvider>
+          <div
+            style={{
+              display: "flex",
+              flexDirection: "column",
+              height: "100vh",
+            }}
+          >
+            <ChatTranscript messages={messages} restoring={false} />
+          </div>
+        </TooltipProvider>
+      </CopilotKitProvider>
+    </QueryClientProvider>,
+  );
+}
diff --git a/app/tests/transcript-rail-clearance.test.tsx b/app/tests/transcript-rail-clearance.test.tsx
new file mode 100644
index 0000000000..aaa0cde558
--- /dev/null
+++ b/app/tests/transcript-rail-clearance.test.tsx
@@ -0,0 +1,208 @@
+import { afterAll, beforeAll, describe, expect, test } from "bun:test";
+import { existsSync, mkdirSync, readFileSync } from "node:fs";
+import { dirname, join } from "node:path";
+import type { Browser, Page } from "playwright-core";
+import { compile } from "tailwindcss";
+
+/**
+ * The rail of turns beside a conversation never sits on the messages. Wherever it draws, the
+ * column's text starts at least 24px to the right of its marks.
+ *
+ * The rail sits in the scroller's left margin, its marks 8px to 40px from the edge. The column is
+ * 768px and centred, so its text starts 16px inside a margin of half of what is left over. With
+ * the rail shown from a 768px scroller, the margin was nothing at 768px and under 40px until about
+ * 850px, and the rail's marks drew over the first letters of the Bot's replies.
+ *
+ * Rendered in a real Chromium, because where the text lands beside the rail is the browser's
+ * layout. The transcript is the real component, bundled from the fixture beside this file; the
+ * stylesheet is the app's own `styles.css` built by Tailwind for exactly the classes on the page.
+ * The window is swept through the widths around where the rail starts to draw.
+ *
+ *   OPENBOT_APP_BROWSER=1 bun test app/tests/transcript-rail-clearance.test.tsx
+ *
+ * With OPENBOT_APP_SHOTS=<dir> it also saves screenshots at 1280px, 900px and 800px wide.
+ */
+const asked = process.env.OPENBOT_APP_BROWSER === "1";
+const shots = process.env.OPENBOT_APP_SHOTS;
+
+const APP = join(import.meta.dir, "..");
+const ORIGIN = "http://openbot.test";
+/** The least room between the rail's marks and the column's text. */
+const CLEARANCE = 24;
+const LAST_REPLY = "Shall I draft the summary";
+
+/** The fixture bundled for the browser. `@/lib/marks` is Vite's `import.meta.glob`, so no marks. */
+async function bundle(): Promise<string> {
+  const built = await Bun.build({
+    entrypoints: [
+      join(import.meta.dir, "transcript-rail-clearance.fixture.tsx"),
+    ],
+    target: "browser",
+    define: { "process.env.NODE_ENV": JSON.stringify("production") },
+    plugins: [
+      {
+        name: "no-marks",
+        setup(build) {
+          build.onResolve({ filter: /^@\/lib\/marks$/ }, () => ({
+            path: "marks",
+            namespace: "no-marks",
+          }));
+          build.onLoad({ filter: /.*/, namespace: "no-marks" }, () => ({
+            contents: "export const markFor = () => null;",
+            loader: "js",
+          }));
+        },
+      },
+    ],
+  });
+  if (!built.success) throw new AggregateError(built.logs, "bundle failed");
+  const script = built.outputs.find((output) => output.kind === "entry-point");
+  if (!script) throw new Error("bundle has no entry point");
+  return script.text();
+}
+
+/** Where `@import "<package>[/<file>]"` lands, by the package's `style` export as Vite reads it. */
+function packageStylesheet(id: string): string {
+  const parts = id.split("/");
+  const name = id.startsWith("@") ? parts.slice(0, 2).join("/") : parts[0];
+  const dir = [
+    join(APP, "node_modules", name),
+    join(APP, "..", "node_modules", name),
+  ].find(existsSync);
+  if (!dir) throw new Error(`no package for ${id}`);
+  const pkg = JSON.parse(readFileSync(join(dir, "package.json"), "utf8"));
+  const subpath = `.${id.slice(name.length)}`;
+  const entry = pkg.exports?.[subpath];
+  const file =
+    typeof entry === "string"
+      ? entry
+      : (entry?.style ?? entry?.default ?? pkg.main ?? "index.css");
+  return join(dir, file);
+}
+
+/** The app's stylesheet, built by Tailwind for these classes, as the app's build does. */
+async function stylesheet(classes: string[]): Promise<string> {
+  const tailwind = dirname(Bun.resolveSync("tailwindcss/package.json", APP));
+  const entry = join(APP, "src", "styles.css");
+  const compiler = await compile(readFileSync(entry, "utf8"), {
+    base: dirname(entry),
+    loadStylesheet: async (id, base) => {
+      const path =
+        id === "tailwindcss"
+          ? join(tailwind, "index.css")
+          : id.startsWith(".")
+            ? join(base, id)
+            : packageStylesheet(id);
+      return { path, base: dirname(path), content: readFileSync(path, "utf8") };
+    },
+  });
+  return compiler.build(classes);
+}
+
+let browser: Browser;
+let script: string;
+
+beforeAll(async () => {
+  if (!asked) return;
+  script = await bundle();
+  const { chromium } = await import("playwright-core");
+  // The CI job installs full Chromium without the headless shell.
+  browser = await chromium.launch({ channel: "chromium" });
+});
+
+afterAll(async () => {
+  await browser?.close();
+});
+
+/** The conversation open in a window this size, styled once it has drawn. */
+async function open(width: number, height: number): Promise<Page> {
+  const page = await browser.newPage({ viewport: { width, height } });
+  page.on("pageerror", (error) => console.error(error));
+  await page.route(`${ORIGIN}/**`, (route) => {
+    const path = new URL(route.request().url()).pathname;
+    if (path === "/")
+      return route.fulfill({
+        contentType: "text/html",
+        body: '<!doctype html><html lang="en"><head><meta charset="utf-8"></head><body><div id="root"></div><script type="module" src="/transcript.js"></script></body></html>',
+      });
+    if (path === "/transcript.js")
+      return route.fulfill({ contentType: "text/javascript", body: script });
+    return route.fulfill({ status: 404 });
+  });
+  await page.goto(`${ORIGIN}/`);
+  await page.getByText(LAST_REPLY).waitFor({ timeout: 8000 });
+  const classes = await page.evaluate(() => [
+    ...new Set(
+      [...document.querySelectorAll("[class]")].flatMap((element) => [
+        ...element.classList,
+      ]),
+    ),
+  ]);
+  await page.addStyleTag({ content: await stylesheet(classes) });
+  return page;
+}
+
+/** Whether the rail draws, its marks' right edge, and where the column's leftmost text starts. */
+function measure(page: Page) {
+  return page.evaluate(async () => {
+    await new Promise((done) =>
+      requestAnimationFrame(() => requestAnimationFrame(done)),
+    );
+    const rail = document.querySelector('nav[aria-label="Turns"]');
+    const marks = [...document.querySelectorAll('[data-slot="rail-mark"]')];
+    const shown = rail !== null && getComputedStyle(rail).display !== "none";
+    const railRight = Math.max(
+      ...marks.map((mark) => mark.getBoundingClientRect().right),
+    );
+    const column = document.querySelector(
+      '[data-slot="message-scroller-content"]',
+    );
+    let textLeft = Number.POSITIVE_INFINITY;
+    if (column) {
+      const walker = document.createTreeWalker(column, NodeFilter.SHOW_TEXT);
+      for (let node = walker.nextNode(); node; node = walker.nextNode()) {
+        if (!node.textContent?.trim()) continue;
+        const range = document.createRange();
+        range.selectNodeContents(node);
+        for (const rect of range.getClientRects()) {
+          if (rect.width > 0) textLeft = Math.min(textLeft, rect.left);
+        }
+      }
+    }
+    return { shown, railRight, textLeft };
+  });
+}
+
+describe.skipIf(!asked)("the rail of turns beside a conversation", () => {
+  test("wherever it draws, the Bot's text starts clear of its marks", async () => {
+    const page = await open(1280, 800);
+    try {
+      const crowded: string[] = [];
+      let drawn = 0;
+      const widths = [];
+      for (let width = 740; width <= 1040; width += 8) widths.push(width);
+      widths.push(1280);
+      for (const width of widths) {
+        await page.setViewportSize({ width, height: 800 });
+        const { shown, railRight, textLeft } = await measure(page);
+        if (!shown) continue;
+        drawn += 1;
+        const gap = Math.round(textLeft - railRight);
+        if (gap < CLEARANCE) crowded.push(`${width}px wide: ${gap}px`);
+      }
+      if (shots) {
+        mkdirSync(shots, { recursive: true });
+        for (const width of [1280, 900, 800]) {
+          await page.setViewportSize({ width, height: 800 });
+          await measure(page);
+          await page.screenshot({ path: join(shots, `${width}.png`) });
+        }
+      }
+      // It does draw where there is room, so the clearance above was measured, not skipped.
+      expect(drawn).toBeGreaterThan(0);
+      expect(crowded).toEqual([]);
+    } finally {
+      await page.close();
+    }
+  }, 60_000);
+});