diff --git a/e2e/agentMarkdown.spec.ts b/e2e/agentMarkdown.spec.ts
new file mode 100644
index 00000000..da15e0e3
--- /dev/null
+++ b/e2e/agentMarkdown.spec.ts
@@ -0,0 +1,130 @@
+/** Markdown in agent replies, in the real conversation: browser defaults don't suit a narrow chat. */
+import { expect, test, type Page } from "@playwright/test";
+
+const TASK = {
+  id: "t1",
+  title: "Repro task",
+  status: "ready" as const,
+  isolation: "local" as const,
+  provider: "codex",
+  model: null,
+  cwd: "/dev/acme-api",
+  branch: null,
+  base: null,
+  baseCommit: null,
+  error: null,
+  createdMs: 0,
+  updatedMs: 0,
+  config: [],
+  commands: [],
+  usage: null,
+  queue: [],
+};
+
+const PIXEL = "data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7";
+const REPLY = [
+  "# Heading one",
+  "",
+  "## Heading two",
+  "",
+  "##### Heading five",
+  "",
+  "> A quote",
+  "",
+  "- [x] done",
+  "- [ ] open",
+  "",
+  "---",
+  "",
+  `![pixel](${PIXEL})`,
+  "",
+  "| Path | Owner | Status | Notes |",
+  "| --- | --- | --- | --- |",
+  "| src/features/agents/conversation/very/long/path/file.tsx | someone | modified | a fairly long note |",
+  "",
+  "```ts",
+  "const a = 1;",
+  "```",
+].join("\n");
+
+async function openReply(page: Page, text: string) {
+  await page.goto("/");
+  await page.getByRole("tree", { name: "Project" }).waitFor();
+  await page.evaluate(
+    async ({ task, text }) => {
+      // Paths go through variables: knip can't resolve these browser-absolute URLs.
+      const storePath = "/src/features/agents/store.ts";
+      const store = await import(storePath);
+      store.useAgents.setState({
+        loaded: true,
+        error: null,
+        providers: [],
+        tasks: new Map([[task.id, task]]),
+        entries: new Map([[task.id, [{ type: "agent", text }]]]),
+        unread: new Set(),
+        docked: null,
+      });
+      store.dockTask(task.id);
+    },
+    { task: TASK, text },
+  );
+  const reply = page.locator("[class*='_markdown_']").first();
+  await reply.locator("h1, p").first().waitFor();
+  return reply;
+}
+
+const css = (reply: ReturnType<Page["locator"]>, selector: string, property: string) =>
+  reply
+    .locator(selector)
+    .first()
+    .evaluate((el, name) => getComputedStyle(el).getPropertyValue(name), property);
+const px = (value: string) => Number.parseFloat(value);
+
+test("styles tables so a reply reads as a table", async ({ page }) => {
+  const reply = await openReply(page, REPLY);
+  expect(await css(reply, "td", "border-top-width")).toBe("1px");
+  expect(await css(reply, "td", "padding-left")).toBe("8px");
+  expect(await css(reply, "th", "border-top-width")).toBe("1px");
+  // A narrow chat must not squeeze a column to a few letters.
+  const widths = await reply
+    .locator("td")
+    .evaluateAll((cells) => cells.map((cell) => cell.getBoundingClientRect().width));
+  for (const width of widths) expect(width).toBeGreaterThanOrEqual(70);
+});
+
+test("scrolls a wide table inside the reply", async ({ page }) => {
+  const reply = await openReply(page, REPLY);
+  const sizes = await reply.evaluate((el) => {
+    const table = el.querySelector("table")!;
+    return { reply: el.clientWidth, table: table.clientWidth, content: table.scrollWidth };
+  });
+  expect(sizes.table).toBeLessThanOrEqual(sizes.reply);
+  expect(sizes.content).toBeGreaterThan(sizes.table);
+});
+
+test("sizes headings for a chat and keeps small ones readable", async ({ page }) => {
+  const reply = await openReply(page, REPLY);
+  const body = px(await css(reply, "td", "font-size"));
+  const h1 = px(await css(reply, "h1", "font-size"));
+  expect(h1).toBeGreaterThan(body);
+  expect(h1).toBeLessThanOrEqual(body * 1.2);
+  expect(px(await css(reply, "h2", "font-size"))).toBeLessThan(h1);
+  expect(px(await css(reply, "h5", "font-size"))).toBe(body);
+});
+
+test("starts and ends a reply without stray margins", async ({ page }) => {
+  const reply = await openReply(page, REPLY);
+  expect(await css(reply, "> :first-child", "margin-top")).toBe("0px");
+  expect(await css(reply, "> :last-child", "margin-bottom")).toBe("0px");
+});
+
+test("styles quotes, rules, images and task lists", async ({ page }) => {
+  const reply = await openReply(page, REPLY);
+  expect(await css(reply, "blockquote", "margin-left")).toBe("0px");
+  expect(await css(reply, "blockquote", "border-left-width")).toBe("3px");
+  expect(await css(reply, "hr", "border-left-width")).toBe("0px");
+  expect(await css(reply, "hr", "border-top-width")).toBe("1px");
+  expect(await css(reply, "img", "max-width")).toBe("100%");
+  // A checkbox stands in for the bullet.
+  expect(await css(reply, "li:has(> input)", "list-style-type")).toBe("none");
+});
diff --git a/src/features/agents/Session.module.css b/src/features/agents/Session.module.css
index 8b18605d..56bc0c96 100644
--- a/src/features/agents/Session.module.css
+++ b/src/features/agents/Session.module.css
@@ -262,6 +262,7 @@
   background: var(--bg-elev);
 }
 .markdown :global(pre) {
+  margin: 0 0 8px;
   padding: 8px 10px;
   border-radius: var(--radius-small);
   background: var(--bg-elev);
@@ -352,6 +353,60 @@
 .markdown :global(a) {
   color: var(--link);
 }
+.markdown :global(table) {
+  display: block;
+  margin: 0 0 8px;
+  overflow: auto;
+  border-collapse: collapse;
+}
+.markdown :global(th),
+.markdown :global(td) {
+  /* `overflow-wrap: anywhere` from .markdown would otherwise squeeze a column to a few letters. */
+  min-width: 6em;
+  border: 1px solid var(--border);
+  padding: 4px 8px;
+}
+.markdown :global(h1),
+.markdown :global(h2),
+.markdown :global(h3),
+.markdown :global(h4),
+.markdown :global(h5),
+.markdown :global(h6) {
+  margin: 12px 0 6px;
+  color: var(--fg-strong);
+  font-size: 1em;
+  line-height: 1.3;
+}
+.markdown :global(h1) {
+  font-size: 1.15em;
+}
+.markdown :global(h2) {
+  font-size: 1.08em;
+}
+.markdown :global(blockquote) {
+  margin: 0 0 8px;
+  padding: 0 10px;
+  border-left: 3px solid var(--border-strong);
+  color: var(--fg-secondary);
+}
+.markdown :global(hr) {
+  margin: 8px 0;
+  border: 0;
+  border-top: 1px solid var(--border);
+}
+.markdown :global(img) {
+  max-width: 100%;
+}
+.markdown :global(li:has(> input[type="checkbox"])) {
+  margin-left: -20px;
+  list-style: none;
+}
+.markdown > :global(:first-child) {
+  margin-top: 0;
+}
+.markdown > :global(:last-child) {
+  margin-bottom: 0;
+}
 
 .thought summary,
 .toolDetails > summary {