diff --git a/apps/web/src/components/chat/MessagesTimeline.test.tsx b/apps/web/src/components/chat/MessagesTimeline.test.tsx
index 3bf5f482948dd9f31fe9bb3e5486c92373e792ef..dae27ccdba473134395d2b7a89a7c13d74f5ff37 100644
--- a/apps/web/src/components/chat/MessagesTimeline.test.tsx
+++ b/apps/web/src/components/chat/MessagesTimeline.test.tsx
@@ -1656,6 +1656,98 @@ describe("MessagesTimeline", () => {
     expect(markup).not.toContain("tool call failed");
   });
 
+  it.each(
+    (
+      [
+        [
+          "**Viewing image first** with *care*, ~~old~~ `code` and [context](https://example.com)",
+          "Viewing image first with care, old code and context",
+          1,
+        ],
+        ["first paragraph\n\nsecond paragraph", "first paragraph second paragraph", 0],
+        ["- first\n- second", "first second", 0],
+        ["first  \nsecond", "first second", 0],
+        ["![image description](image.png)", "image description", 0],
+        ["![](image.png)", "Thought", 0],
+        ["---", "Thought", 0],
+      ] as const
+    ).flatMap(([markdown, expected, strongCount]) =>
+      [false, true].map((streaming) => ({
+        markdown,
+        expected,
+        strongCount,
+        streaming,
+      })),
+    ),
+  )(
+    "shows a plain thought preview for $markdown, streaming=$streaming",
+    async ({ markdown, expected, strongCount, streaming }) => {
+      vi.stubGlobal("IS_REACT_ACT_ENVIRONMENT", true);
+      vi.stubGlobal("requestAnimationFrame", () => 0);
+      vi.stubGlobal("cancelAnimationFrame", () => {});
+      const turnId = TurnId.make("turn-thought");
+      const thought = buildAssistantTimelineEntry(markdown);
+      let renderer: ReactTestRenderer | undefined;
+      try {
+        await act(() => {
+          renderer = create(
+            <MessagesTimeline
+              {...buildProps()}
+              isWorking
+              runningTurnId={turnId}
+              timelineEntries={[
+                {
+                  id: "work-entry",
+                  kind: "work",
+                  createdAt: MESSAGE_CREATED_AT,
+                  entry: {
+                    id: "work",
+                    createdAt: MESSAGE_CREATED_AT,
+                    turnId,
+                    label: "Read image",
+                    tone: "tool",
+                    itemType: "command_execution",
+                    command: "cat image.png",
+                    toolLifecycleStatus: "completed",
+                  },
+                },
+                {
+                  ...thought,
+                  message: { ...thought.message, role: "reasoning", turnId, streaming },
+                },
+              ]}
+            />,
+          );
+        });
+        await act(() => renderer!.root.findByProps({ "aria-expanded": false }).props.onClick());
+        const text = renderer!.root.findByProps({
+          className: "relative min-w-0 flex-1 truncate text-secondary-label",
+        });
+        const preview = text.parent!;
+        expect(
+          text
+            .findAll(() => true)
+            .flatMap((node) => node.children)
+            .filter((child) => typeof child === "string")
+            .join(""),
+        ).toBe(
+          (streaming && expected === "Thought" ? "Thinking" : expected).repeat(streaming ? 2 : 1),
+        );
+        expect(
+          preview.findAll((node) =>
+            ["strong", "em", "del", "code", "a"].includes(String(node.type)),
+          ),
+        ).toHaveLength(0);
+        await act(() => preview.props.onClick());
+        expect(renderer!.root.findAllByType("strong")).toHaveLength(strongCount);
+        await act(() => preview.props.onClick());
+        expect(renderer!.root.findAllByType("strong")).toHaveLength(0);
+      } finally {
+        await act(() => renderer?.unmount());
+      }
+    },
+  );
+
   it("renders initial thinking as the shared live activity row", () => {
     const turnId = TurnId.make("turn-live");
     const markup = renderToStaticMarkup(
diff --git a/apps/web/src/components/chat/MessagesTimeline.tsx b/apps/web/src/components/chat/MessagesTimeline.tsx
index 8305cb1d5283ba8aad221e73ba83ab43dad65eab..42a45b9910281f72c479bdd9ed358cdbd53ff342 100644
--- a/apps/web/src/components/chat/MessagesTimeline.tsx
+++ b/apps/web/src/components/chat/MessagesTimeline.tsx
@@ -103,6 +103,9 @@ import {
 } from "../../lib/diffRendering";
 import { PREFERRED_HIGHLIGHTER } from "../../lib/syntaxHighlighting";
 import ChatMarkdown, { ChatMarkdownAssetImage } from "../ChatMarkdown";
+import ReactMarkdown from "react-markdown";
+import remarkGfm from "remark-gfm";
+import type { Root, RootContent } from "mdast";
 import { T3Wordmark } from "../T3Wordmark";
 import {
   BotIcon,
@@ -2689,6 +2692,28 @@ function ThinkingTimelineRow() {
   );
 }
 
+function remarkThoughtPreview(fallback: string) {
+  return (tree: Root) => {
+    const plainText = (node: Root | RootContent): string => {
+      if (node.type === "html" || node.type === "definition") return "";
+      if ("alt" in node) return node.alt ?? "";
+      if ("value" in node) return node.value;
+      if ("children" in node) {
+        const separator = ["root", "blockquote", "list", "listItem", "table", "tableRow"].includes(
+          node.type,
+        )
+          ? " "
+          : "";
+        return node.children.map(plainText).join(separator);
+      }
+      return node.type === "break" ? " " : "";
+    };
+    tree.children = [
+      { type: "text", value: plainText(tree).replace(/\s+/g, " ").trim() || fallback },
+    ];
+  };
+}
+
 /**
  * Thinking inside a tool group has its own disclosure, preserved across recycling.
  * A group whose row already reads "Thought" (no visible tool) skips the header.
@@ -2722,7 +2747,13 @@ function ReasoningTraceBlock({
   }
   const label = streaming ? "Thinking" : "Thought";
   const collapsedPreview = messages.find((message) => message.text.trim().length > 0)?.text.trim();
-  const headerText = expanded ? label : (collapsedPreview ?? label);
+  const headerText = expanded ? (
+    label
+  ) : (
+    <ReactMarkdown remarkPlugins={[remarkGfm, [remarkThoughtPreview, label]]}>
+      {collapsedPreview ?? label}
+    </ReactMarkdown>
+  );
   return (
     <div className="flex flex-col">
       {showHeader ? (