Merge pull request #7940 from SivanCola/fix/thinking-trace-markdown

Render thinking traces as Markdown without stream lag / 流畅渲染思考过程 Markdown

desktop/frontend/src/__tests__/mermaid-rendering.test.tsx

@@ -257,6 +257,12 @@ console.log("\nmermaid rendering");
   });
   eq(pendingFrame, undefined, "tail growth alone schedules no further parse");
 
+  await act(async () => {
+    root.render(<MarkdownTextProbe text={"...\nreplacement window"} streaming />);
+    await flushTimers();
+  });
+  eq(rootEl.textContent, "", "a rolling Markdown window drops its stale parsed prefix before paint");
+
   await act(async () => {
     root.render(<MarkdownTextProbe text="complete" streaming={false} />);
   });

desktop/frontend/src/__tests__/message-reasoning-panel.test.tsx

@@ -1,11 +1,21 @@
 // Run: tsx src/__tests__/message-reasoning-panel.test.tsx
 
 import { JSDOM } from "jsdom";
+import { registerHooks } from "node:module";
 import React, { act } from "react";
 import { createRoot } from "react-dom/client";
 import { LocaleProvider } from "../lib/i18n";
 import { AssistantMessage } from "../components/Message";
 
+registerHooks({
+  resolve(specifier, context, nextResolve) {
+    if (specifier.endsWith(".css")) {
+      return nextResolve("./asset-stub-for-tests.ts", { ...context, parentURL: import.meta.url });
+    }
+    return nextResolve(specifier, context);
+  },
+});
+
 let passed = 0;
 let failed = 0;
 
@@ -30,6 +40,7 @@ globalThis.window = dom.window as unknown as Window & typeof globalThis;
 globalThis.document = dom.window.document;
 Object.defineProperty(globalThis, "navigator", { configurable: true, value: { ...dom.window.navigator, language: "en-US" } });
 globalThis.Node = dom.window.Node;
+globalThis.Element = dom.window.Element;
 globalThis.HTMLElement = dom.window.HTMLElement;
 globalThis.Event = dom.window.Event;
 globalThis.MouseEvent = dom.window.MouseEvent;
@@ -49,7 +60,7 @@ await act(async () => {
           kind: "assistant",
           id: "a1",
           text: "",
-          reasoning: "line one\nline two",
+          reasoning: "**important trace**\n\n- line one\n- line two\n\n`inline code`",
           streaming: false,
           reasoningComplete: true,
           reasoningDurationMs: 2_600,
@@ -67,9 +78,13 @@ ok(!document.querySelector(".reasoning__body"), "completed reasoning is collapse
 
 await act(async () => {
   header?.dispatchEvent(new dom.window.MouseEvent("click", { bubbles: true }));
+  await new Promise((resolve) => setTimeout(resolve, 0));
 });
 
 ok(document.querySelector(".reasoning__body")?.textContent?.includes("line two") ?? false, "clicking the header expands the reasoning body");
+ok(document.querySelector(".reasoning__body strong")?.textContent === "important trace", "reasoning renders Markdown emphasis");
+ok(document.querySelectorAll(".reasoning__body li").length === 2, "reasoning renders Markdown lists");
+ok(document.querySelector(".reasoning__body .md-code")?.textContent === "inline code", "reasoning renders Markdown inline code");
 
 await act(async () => {
   root.unmount();

desktop/frontend/src/__tests__/reasoning-display.test.ts

@@ -41,5 +41,17 @@ eq(
   "can opt out of streaming truncation",
 );
 
+eq(
+  displayReasoningText("abcdefgh", { streaming: true, maxChars: 4, maxLines: 10, stableWindowChars: 3 }),
+  "...\ndefgh",
+  "keeps a stable append-only character window between coarse rebases",
+);
+
+eq(
+  displayReasoningText("a\nb\nc\nd\ne", { streaming: true, maxChars: 100, maxLines: 2, stableWindowLines: 2 }),
+  "...\nc\nd\ne",
+  "keeps a stable append-only line window between coarse rebases",
+);
+
 console.log(`\n${passed} passed, ${failed} failed`);
 if (failed > 0) process.exit(1);

desktop/frontend/src/__tests__/subagent-progress-card.test.tsx

@@ -5,6 +5,7 @@
 // response preview / notices), including the terminal phase visuals.
 
 import { JSDOM } from "jsdom";
+import { registerHooks } from "node:module";
 import React from "react";
 import { act } from "react";
 import { createRoot } from "react-dom/client";
@@ -13,6 +14,15 @@ import { ToolCard } from "../components/ToolCard";
 import { LocaleProvider } from "../lib/i18n";
 import type { Item, SubagentProgress } from "../lib/useController";
 
+registerHooks({
+  resolve(specifier, context, nextResolve) {
+    if (specifier.endsWith(".css")) {
+      return nextResolve("./asset-stub-for-tests.ts", { ...context, parentURL: import.meta.url });
+    }
+    return nextResolve(specifier, context);
+  },
+});
+
 type ToolItem = Extract<Item, { kind: "tool" }>;
 
 // jsdom has no layout engine: stub the GSAP tween surface the collapse hook
@@ -94,7 +104,7 @@ function makeItem(phase: SubagentProgress["phase"], over: Partial<SubagentProgre
     status: phase === "completed" || phase === "failed" ? "done" : phase === "cancelled" ? "stopped" : "running",
     subagentProgress: {
       phase,
-      reasoning: "thinking step by step",
+      reasoning: "**thinking** step by step\n\n- inspect\n- verify",
       text: "draft answer preview",
       notice: "heads up",
       lastActivityAt: now - 3_000,
@@ -131,6 +141,7 @@ console.log("\nsubagent progress card");
   // Expanded body shows reasoning / response / notices without ordinary output.
   const head = document.querySelector(".tool__head") as HTMLButtonElement | null;
   ok(!!head, "card head renders");
+  ok(!document.querySelector(".tool__subagent-preview-text .md"), "collapsed reasoning preview skips Markdown rendering");
   await act(async () => {
     head?.click();
     await flushTimers();
@@ -138,6 +149,8 @@ console.log("\nsubagent progress card");
   ok(!!document.querySelector(".tool__subagent-preview"), "expanded body renders the preview block");
   ok(document.querySelector(".tool__subagent-preview-label")?.textContent === "Reasoning", "reasoning section label");
   ok(document.body.textContent?.includes("thinking step by step"), "reasoning preview text visible");
+  ok(document.querySelector(".tool__subagent-preview-text strong")?.textContent === "thinking", "reasoning preview renders Markdown emphasis");
+  ok(document.querySelectorAll(".tool__subagent-preview-text li").length === 2, "reasoning preview renders Markdown lists");
   ok(document.body.textContent?.includes("draft answer preview"), "response preview text visible");
   ok(document.body.textContent?.includes("heads up"), "notice preview text visible");
 

desktop/frontend/src/__tests__/ui-perf-scenarios.test.ts

@@ -32,7 +32,8 @@ const FRAME_MS = 1000 / 60;
 interface SimResult {
   frames: number;
   commits: number;
-  markdownParses: number;
+  answerMarkdownParses: number;
+  reasoningMarkdownParses: number;
   itemsIdentityBreaks: number;
   bumpSkipViolations: number;
   state: typeof initialState;
@@ -49,15 +50,20 @@ function simulate(spec: UIPerfScenario, base?: typeof initialState): SimResult {
 
   let frames = 0;
   let commits = 0;
-  let markdownParses = 0;
+  let answerMarkdownParses = 0;
+  let reasoningMarkdownParses = 0;
   let itemsIdentityBreaks = 0;
   let bumpSkipViolations = 0;
   let text = "";
-  let renderedLen = 0;
-  let lastParseAt = -Infinity;
+  let reasoning = "";
+  let answerRenderedLen = 0;
+  let reasoningRenderedLen = 0;
+  let lastAnswerParseAt = -Infinity;
+  let lastReasoningParseAt = -Infinity;
   let pendingChunks = 0;
   let index = 0;
   let firstBatch = true;
+  let reasoningFinalized = false;
 
   while (index < chunks.length) {
     frames += 1;
@@ -68,6 +74,7 @@ function simulate(spec: UIPerfScenario, base?: typeof initialState): SimResult {
       index += 1;
       pendingChunks -= 1;
       if (chunk.kind === "text") text += chunk.delta;
+      else reasoning += chunk.delta;
       batch.push({ tabId: "a", e: { kind: chunk.kind, text: chunk.delta } as WireEvent });
     }
     if (batch.length === 0) continue;
@@ -85,17 +92,31 @@ function simulate(spec: UIPerfScenario, base?: typeof initialState): SimResult {
       firstBatch = false;
     }
     const nowMs = frames * FRAME_MS;
-    if (nowMs - lastParseAt >= streamingMarkdownCommitInterval(text.length)) {
+    if (spec.reasoningVisible && reasoning.length > 0 && text.length > 0 && !reasoningFinalized) {
+      reasoningMarkdownParses += 1;
+      reasoningRenderedLen = reasoning.length;
+      reasoningFinalized = true;
+    }
+    if (spec.reasoningVisible && !reasoningFinalized && nowMs - lastReasoningParseAt >= streamingMarkdownCommitInterval(reasoning.length)) {
+      const target = streamingCommitTarget(reasoning);
+      if (target.length > reasoningRenderedLen) {
+        reasoningMarkdownParses += 1;
+        reasoningRenderedLen = target.length;
+        lastReasoningParseAt = nowMs;
+      }
+    }
+    if (nowMs - lastAnswerParseAt >= streamingMarkdownCommitInterval(text.length)) {
       const target = streamingCommitTarget(text);
-      if (target.length > renderedLen) {
-        markdownParses += 1;
-        renderedLen = target.length;
-        lastParseAt = nowMs;
+      if (target.length > answerRenderedLen) {
+        answerMarkdownParses += 1;
+        answerRenderedLen = target.length;
+        lastAnswerParseAt = nowMs;
       }
     }
   }
-  markdownParses += 1; // end-of-stream finalization parse
-  return { frames, commits, markdownParses, itemsIdentityBreaks, bumpSkipViolations, state };
+  if (text.length > answerRenderedLen) answerMarkdownParses += 1;
+  if (spec.reasoningVisible && reasoning.length > reasoningRenderedLen) reasoningMarkdownParses += 1;
+  return { frames, commits, answerMarkdownParses, reasoningMarkdownParses, itemsIdentityBreaks, bumpSkipViolations, state };
 }
 
 const byId = new Map(UI_PERF_SCENARIOS.map((s) => [s.id, s]));
@@ -111,8 +132,8 @@ const scenario = (id: string): UIPerfScenario => {
   const r = simulate(spec);
   ok(r.commits <= r.frames + 1, `01: one reducer pass per frame at most (${r.commits} commits / ${r.frames} frames)`);
   ok(
-    r.markdownParses <= spec.paragraphs + 3,
-    `01: markdown parses bounded by blocks, not ticks (${r.markdownParses} for ${spec.paragraphs} paragraphs)`,
+    r.answerMarkdownParses <= spec.paragraphs + 3,
+    `01: markdown parses bounded by blocks, not ticks (${r.answerMarkdownParses} for ${spec.paragraphs} paragraphs)`,
   );
   ok(r.state.live !== undefined && r.state.live.text.length >= spec.textChars, "01: full answer reached the live stream");
 }
@@ -123,7 +144,8 @@ const scenario = (id: string): UIPerfScenario => {
   const r = simulate(spec);
   const seconds = r.frames / 60;
   ok(r.commits / seconds <= 61, `02: state commits stay at or under display FPS (${(r.commits / seconds).toFixed(1)}/s)`);
-  ok(r.markdownParses <= spec.paragraphs + 3, `02: reasoning stream causes no markdown parses (${r.markdownParses})`);
+  ok(r.reasoningMarkdownParses <= 2, `02: visible reasoning Markdown stays within its parse budget (${r.reasoningMarkdownParses})`);
+  ok(r.answerMarkdownParses <= spec.paragraphs + 3, `02: answer Markdown keeps its existing parse budget (${r.answerMarkdownParses})`);
   ok(r.state.live !== undefined && r.state.live.reasoning.length >= spec.reasoningChars, "02: full reasoning reached the live stream");
   eq(r.state.live?.reasoningComplete, true, "02: answer text after reasoning completed it");
 }
@@ -134,12 +156,12 @@ const scenario = (id: string): UIPerfScenario => {
   const r = simulate(spec);
   ok(r.commits <= r.frames + 1, `03: commits bounded by frames (${r.commits}/${r.frames})`);
   ok(
-    r.markdownParses >= spec.codeFences,
-    `03: open fences keep committing so streamed code stays highlighted (${r.markdownParses} parses)`,
+    r.answerMarkdownParses >= spec.codeFences,
+    `03: open fences keep committing so streamed code stays highlighted (${r.answerMarkdownParses} parses)`,
   );
   ok(
-    r.markdownParses <= Math.ceil(r.frames / 3) + spec.paragraphs + spec.codeFences,
-    `03: parse cadence capped by the 50ms tier even inside fences (${r.markdownParses} parses / ${r.frames} frames)`,
+    r.answerMarkdownParses <= Math.ceil(r.frames / 3) + spec.paragraphs + spec.codeFences,
+    `03: parse cadence capped by the 50ms tier even inside fences (${r.answerMarkdownParses} parses / ${r.frames} frames)`,
   );
 }
 
@@ -168,6 +190,7 @@ const scenario = (id: string): UIPerfScenario => {
 {
   const r = simulate(scenario("UI-PERF-06"));
   eq(r.bumpSkipViolations, 0, "06: background streaming never trips the whole-App bump — liveStore only");
+  eq(r.reasoningMarkdownParses, 0, "06: background reasoning performs no Markdown parsing");
 }
 
 process.stdout.write(`\n${passed} passed, ${failed} failed\n`);

desktop/frontend/src/components/Markdown.tsx

@@ -191,6 +191,13 @@ export function useRenderedMarkdownText(text: string, streaming: boolean): strin
       cancelFinalizationRef.current?.();
       cancelFinalizationRef.current = null;
       finalizingTextRef.current = null;
+      // A bounded live preview occasionally advances its window and drops an
+      // old prefix. Discard the stale parsed tree before paint; the complete
+      // replacement stays visible through StreamingMarkdownTail and is parsed
+      // later under the normal adaptive budget.
+      if (renderedText !== "" && !text.startsWith(renderedText)) {
+        setRenderedText("");
+      }
       return;
     }
     lastCommitAtRef.current = 0;

desktop/frontend/src/components/Message.tsx

@@ -13,7 +13,7 @@ import { useT } from "../lib/i18n";
 import { ImageViewer } from "./ImageViewer";
 import { Tooltip } from "./Tooltip";
 import { useGSAPCollapse } from "../lib/useGSAPCollapse";
-import { displayReasoningText } from "../lib/reasoningDisplay";
+import { displayReasoningText, STREAMING_REASONING_WINDOW_STEP_CHARS, STREAMING_REASONING_WINDOW_STEP_LINES } from "../lib/reasoningDisplay";
 import { stripMemoryCompilerExecution } from "../lib/memoryCompilerDisplay";
 import { visibleTranscriptMemoryCitations } from "../lib/memoryCitationVisibility";
 import { invocationSegmentsFromMessage, type InvocationMetadataMap } from "../lib/invocationDisplay";
@@ -914,8 +914,8 @@ function ReasoningPanel({
   const isReasoningRunning = item.streaming && !item.reasoningComplete;
   const visibleReasoning = reasoningOpen
     ? displayReasoningText(item.reasoning, {
-        streaming: item.streaming,
-        truncateStreaming: truncateStreamingReasoning,
+        streaming: isReasoningRunning,
+        truncateStreaming: truncateStreamingReasoning, stableWindowChars: STREAMING_REASONING_WINDOW_STEP_CHARS, stableWindowLines: STREAMING_REASONING_WINDOW_STEP_LINES,
       })
     : "";
   const label = isReasoningRunning ? t("msg.thinkingRunning") : t("msg.thinking");
@@ -936,7 +936,7 @@ function ReasoningPanel({
         <ChevronRight className={`reasoning__chevron${reasoningOpen ? " reasoning__chevron--open" : ""}`} size={12} />
       </button>
       {reasoningOpen && (
-        <div ref={reasoningBodyRef} className="reasoning__body">{visibleReasoning}</div>
+        <div ref={reasoningBodyRef} className="reasoning__body"><Markdown text={visibleReasoning} streaming={isReasoningRunning} /></div>
       )}
     </div>
   );

desktop/frontend/src/components/ToolCard.tsx

@@ -9,6 +9,7 @@ import { useGSAPCollapse } from "../lib/useGSAPCollapse";
 import { isTerminalSubagentPhase, type Item, type SubagentPhase } from "../lib/useController";
 import type { Translator } from "../lib/i18n";
 import { ReadOnlyBatch } from "./ReadOnlyBatch";
+import { Markdown } from "./Markdown";
 
 type ToolItem = Extract<Item, { kind: "tool" }>;
 
@@ -357,7 +358,13 @@ export const ToolCard = memo(function ToolCard({ item, subcalls, tabId, displayN
             {sp.reasoning && (
               <div className="tool__subagent-preview-section">
                 <div className="tool__subagent-preview-label">{t("subagent.preview.reasoning")}</div>
-                <pre className="tool__subagent-preview-text">{sp.reasoning}</pre>
+                {open ? (
+                  <div className="tool__subagent-preview-text tool__subagent-preview-text--markdown">
+                    <Markdown text={sp.reasoning} streaming={sp.phase === "reasoning"} />
+                  </div>
+                ) : (
+                  <pre className="tool__subagent-preview-text">{sp.reasoning}</pre>
+                )}
               </div>
             )}
             {sp.text && (

desktop/frontend/src/components/Transcript.tsx

@@ -19,8 +19,9 @@ import { useEntranceAnimation } from "../lib/useEntranceAnimation";
 import { useScrollManager } from "../lib/useScrollManager";
 import { buildTurnGroups, compactQuestionText, createWarmLayerState, lastQuestionTurn, questionAnchorId, questionTurnsById, scrollVersion, warmColdPageForTurn, warmLayerWithColdPageAtLeast, warmLayerWithExpandedTurn, warmLayerWithNextColdPage, warmPagination, warmUserPreview, type QuestionAnchor, type TurnGroup, type WarmLayerState } from "../lib/transcriptGrouping";
 import { appendTurnActionCopyText } from "../lib/turnActionCopy";
-import { displayReasoningText } from "../lib/reasoningDisplay";
+import { displayReasoningText, STREAMING_REASONING_WINDOW_STEP_CHARS, STREAMING_REASONING_WINDOW_STEP_LINES } from "../lib/reasoningDisplay";
 import { observeScrollContentSize } from "../lib/scrollContentObserver";
+import { Markdown } from "./Markdown";
 
 type ToolItem = Extract<Item, { kind: "tool" }>;
 type AssistantItem = Extract<Item, { kind: "assistant" }>;
@@ -81,7 +82,7 @@ const LiveAssistantMessage = memo(function LiveAssistantMessage({
   );
 });
 
-function InlineAssistantReasoning({ item }: { item: AssistantItem }) {
+function InlineAssistantReasoning({ item, active }: { item: AssistantItem; active: boolean }) {
   const t = useT();
   const live = useContext(LiveStreamContext);
   const [open, setOpen] = useState(true);
@@ -94,13 +95,12 @@ function InlineAssistantReasoning({ item }: { item: AssistantItem }) {
         reasoningComplete: live.reasoningComplete,
       }
     : item;
-  const reasoning = shown.reasoning.trim();
+  const reasoning = shown.reasoning.trim(); const running = shown.streaming && !shown.reasoningComplete;
   if (!reasoning) return null;
   const visibleReasoning = displayReasoningText(shown.reasoning, {
-    streaming: shown.streaming,
-    truncateStreaming: true,
+    streaming: running,
+    truncateStreaming: true, stableWindowChars: STREAMING_REASONING_WINDOW_STEP_CHARS, stableWindowLines: STREAMING_REASONING_WINDOW_STEP_LINES,
   });
-  const running = shown.streaming && !shown.reasoningComplete;
   return (
     <div className={`turn-collapse__reasoning-phase${open ? " turn-collapse__reasoning-phase--open" : ""}`}>
       <button
@@ -114,7 +114,7 @@ function InlineAssistantReasoning({ item }: { item: AssistantItem }) {
         <span>{running ? t("msg.thinkingRunning") : t("msg.thinking")}</span>
         <ChevronRight className={`reasoning__chevron${open ? " reasoning__chevron--open" : ""}`} size={12} />
       </button>
-      <div ref={bodyRef} className="turn-collapse__inline-reasoning">{visibleReasoning}</div>
+      <div ref={bodyRef} className="turn-collapse__inline-reasoning">{active && open ? <Markdown text={visibleReasoning} streaming={running} /> : visibleReasoning}</div>
     </div>
   );
 }
@@ -1525,7 +1525,7 @@ function TurnCollapse({ items, durationMs, mode, subcalls, tabId, creationMode =
       case "assistant":
         // Answer text renders outside the fold (partitionTurnItems strips it),
         // so the fold only ever shows the reasoning segment.
-        body.push(<InlineAssistantReasoning key={`${it.id}-reasoning`} item={it as AssistantItem} />);
+        body.push(<InlineAssistantReasoning key={`${it.id}-reasoning`} item={it as AssistantItem} active={open} />);
         break;
     }
   }

desktop/frontend/src/lib/reasoningDisplay.ts

@@ -1,11 +1,15 @@
 export const STREAMING_REASONING_TAIL_CHARS = 12_000;
 export const STREAMING_REASONING_TAIL_LINES = 240;
+export const STREAMING_REASONING_WINDOW_STEP_CHARS = 2_000;
+export const STREAMING_REASONING_WINDOW_STEP_LINES = 40;
 
 type ReasoningDisplayOptions = {
   streaming: boolean;
   truncateStreaming?: boolean;
   maxChars?: number;
   maxLines?: number;
+  stableWindowChars?: number;
+  stableWindowLines?: number;
 };
 
 export function displayReasoningText(
@@ -15,6 +19,8 @@ export function displayReasoningText(
     truncateStreaming = true,
     maxChars = STREAMING_REASONING_TAIL_CHARS,
     maxLines = STREAMING_REASONING_TAIL_LINES,
+    stableWindowChars = 0,
+    stableWindowLines = 0,
   }: ReasoningDisplayOptions,
 ): string {
   if (!streaming || !truncateStreaming) return reasoning;
@@ -23,15 +29,27 @@ export function displayReasoningText(
   let truncated = false;
 
   if (maxChars > 0 && text.length > maxChars) {
-    text = text.slice(-maxChars);
-    truncated = true;
+    const overflow = text.length - maxChars;
+    const start = stableWindowChars > 0
+      ? Math.floor(overflow / stableWindowChars) * stableWindowChars
+      : overflow;
+    if (start > 0) {
+      text = text.slice(start);
+      truncated = true;
+    }
   }
 
   if (maxLines > 0) {
     const lines = text.split(/\r?\n/);
     if (lines.length > maxLines) {
-      text = lines.slice(-maxLines).join("\n");
-      truncated = true;
+      const overflow = lines.length - maxLines;
+      const start = stableWindowLines > 0
+        ? Math.floor(overflow / stableWindowLines) * stableWindowLines
+        : overflow;
+      if (start > 0) {
+        text = lines.slice(start).join("\n");
+        truncated = true;
+      }
     }
   }
 

desktop/frontend/src/lib/uiPerfScenarios.ts

@@ -11,6 +11,7 @@ export interface UIPerfScenario {
   title: string;
   chunksPerSec: number;
   reasoningChars: number;
+  reasoningVisible: boolean;
   textChars: number;
   paragraphs: number;
   codeFences: number;
@@ -26,6 +27,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "normal answer: 2KB markdown prose",
     chunksPerSec: 80,
     reasoningChars: 0,
+    reasoningVisible: false,
     textChars: 2_000,
     paragraphs: 8,
     codeFences: 0,
@@ -36,6 +38,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "DeepSeek reasoning: 16KB reasoning + 8KB answer",
     chunksPerSec: 150,
     reasoningChars: 16_000,
+    reasoningVisible: true,
     textChars: 8_000,
     paragraphs: 16,
     codeFences: 0,
@@ -46,6 +49,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "code heavy: 10 fences in 20KB markdown",
     chunksPerSec: 120,
     reasoningChars: 0,
+    reasoningVisible: false,
     textChars: 20_000,
     paragraphs: 10,
     codeFences: 10,
@@ -56,6 +60,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "interaction under streaming: typing, wheel, selection, tool cards",
     chunksPerSec: 150,
     reasoningChars: 8_000,
+    reasoningVisible: true,
     textChars: 8_000,
     paragraphs: 12,
     codeFences: 2,
@@ -67,6 +72,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "long session: 100 turns, 30 tool calls, diffs and code",
     chunksPerSec: 100,
     reasoningChars: 0,
+    reasoningVisible: false,
     textChars: 4_000,
     paragraphs: 10,
     codeFences: 2,
@@ -78,6 +84,7 @@ export const UI_PERF_SCENARIOS: UIPerfScenario[] = [
     title: "background agent: tab A streams while tab B is active",
     chunksPerSec: 150,
     reasoningChars: 4_000,
+    reasoningVisible: false,
     textChars: 4_000,
     paragraphs: 8,
     codeFences: 0,

desktop/frontend/src/styles.css

@@ -4963,6 +4963,25 @@ a[href] {
   line-height: 1.72;
   white-space: pre-wrap;
 }
+.reasoning__body > .md,
+.turn-collapse__inline-reasoning > .md,
+.tool__subagent-preview-text--markdown > .md {
+  color: inherit;
+  font-size: inherit;
+  line-height: inherit;
+  white-space: normal;
+}
+.reasoning__body > .md p,
+.turn-collapse__inline-reasoning > .md p,
+.tool__subagent-preview-text--markdown > .md p {
+  margin-bottom: 8px;
+}
+.reasoning__body > .md :where(h1, h2, h3, h4),
+.turn-collapse__inline-reasoning > .md :where(h1, h2, h3, h4),
+.tool__subagent-preview-text--markdown > .md :where(h1, h2, h3, h4) {
+  margin: 12px 0 6px;
+  font-size: 1em;
+}
 /* ── markdown prose ──────────────────────────────────────────────────────── */
 .md {
   font-family: var(--font-content-family);