feat: implement auto-follow viewport for live test results

- Added AutoFollowViewport component to automatically scroll to the latest test results.
- Integrated auto-follow functionality into AutoTestLivePanel for improved user experience during test execution.
- Introduced logic to manage following state and handle scroll events effectively.

frontend/src/components/assistant-editor/debug-auto-test.tsx

@@ -11,6 +11,7 @@
 import type React from "react";
 import { useCallback, useEffect, useMemo, useRef, useState } from "react";
 import {
+  ArrowDown,
   Check,
   ChevronDown,
   FlaskConical,
@@ -57,6 +58,7 @@ import {
 import { cn } from "@/lib/utils";
 
 const RUN_POLL_MS = 1000;
+const AUTO_FOLLOW_BOTTOM_THRESHOLD_PX = 32;
 
 export type AutoTestPhase =
   | "idle"
@@ -253,6 +255,84 @@ function CasePicker({
 
 // ─── Result panel ───────────────────────────────────────────────────────────
 
+function AutoFollowViewport({
+  children,
+  followKey,
+}: {
+  children: React.ReactNode;
+  followKey: string;
+}) {
+  const scrollRef = useRef<HTMLDivElement>(null);
+  const contentRef = useRef<HTMLDivElement>(null);
+  const isFollowingRef = useRef(true);
+  const [isFollowing, setIsFollowing] = useState(true);
+
+  const updateFollowing = useCallback((next: boolean) => {
+    isFollowingRef.current = next;
+    setIsFollowing((current) => (current === next ? current : next));
+  }, []);
+
+  const scrollToLatest = useCallback(() => {
+    const viewport = scrollRef.current;
+    if (!viewport) return;
+    viewport.scrollTop = viewport.scrollHeight;
+  }, []);
+
+  const handleScroll = useCallback(() => {
+    const viewport = scrollRef.current;
+    if (!viewport) return;
+    const distanceFromBottom =
+      viewport.scrollHeight - viewport.scrollTop - viewport.clientHeight;
+    updateFollowing(distanceFromBottom <= AUTO_FOLLOW_BOTTOM_THRESHOLD_PX);
+  }, [updateFollowing]);
+
+  useEffect(() => {
+    if (!isFollowingRef.current) return;
+    const frame = window.requestAnimationFrame(scrollToLatest);
+    return () => window.cancelAnimationFrame(frame);
+  }, [followKey, scrollToLatest]);
+
+  // Runtime cards and images can grow after the test snapshot is rendered.
+  useEffect(() => {
+    const content = contentRef.current;
+    if (!content) return;
+    const observer = new ResizeObserver(() => {
+      if (isFollowingRef.current) scrollToLatest();
+    });
+    observer.observe(content);
+    return () => observer.disconnect();
+  }, [scrollToLatest]);
+
+  const resumeFollowing = useCallback(() => {
+    updateFollowing(true);
+    scrollToLatest();
+  }, [scrollToLatest, updateFollowing]);
+
+  return (
+    <div className="relative flex min-h-0 flex-1">
+      <div
+        ref={scrollRef}
+        onScroll={handleScroll}
+        className="scrollbar-subtle min-h-0 flex-1 overflow-y-auto px-5 py-4"
+      >
+        <div ref={contentRef}>{children}</div>
+      </div>
+      {!isFollowing && (
+        <Button
+          type="button"
+          size="sm"
+          variant="secondary"
+          onClick={resumeFollowing}
+          className="absolute bottom-4 left-1/2 h-8 -translate-x-1/2 gap-1.5 rounded-full border border-hairline bg-background/95 px-3 text-xs shadow-md backdrop-blur"
+        >
+          <ArrowDown size={13} />
+          回到最新
+        </Button>
+      )}
+    </div>
+  );
+}
+
 export function AutoTestLivePanel({
   testCase,
   state,
@@ -353,10 +433,26 @@ export function AutoTestLivePanel({
 
   const turns = state.runCase?.turns ?? [];
   const startup = state.runCase?.startup;
+  const autoFollowKey = [
+    state.phase,
+    startup?.completed ? 1 : 0,
+    startup?.assistantOutputs.length ?? 0,
+    startup?.runtimeRecords?.length ?? 0,
+    ...turns.map(
+      (turn) =>
+        `${turn.id}:${turn.runtimeRecords?.length ?? 0}:${turn.toolCalls.length}:${turn.evaluations.length}`,
+    ),
+    state.runCase?.overallCriteria.length ?? 0,
+  ].join("|");
+  const autoFollowResetKey = state.run?.id ?? state.selectedId ?? "auto-test";
+
   if (turns.length === 0) {
     if (startup?.completed) {
       return (
-        <div className="scrollbar-subtle min-h-0 flex-1 overflow-y-auto px-5 py-4">
+        <AutoFollowViewport
+          key={autoFollowResetKey}
+          followKey={autoFollowKey}
+        >
           <AutoTestTimeline
             startup={startup}
             turns={[]}
@@ -366,7 +462,7 @@ export function AutoTestLivePanel({
             <Loader2 size={13} className="animate-spin" />
             正在执行第 1 轮固定输入…
           </div>
-        </div>
+        </AutoFollowViewport>
       );
     }
     return (
@@ -382,7 +478,10 @@ export function AutoTestLivePanel({
     state.phase === "running" && state.currentTurn >= state.maxTurns;
 
   return (
-    <div className="scrollbar-subtle flex min-h-0 flex-1 flex-col overflow-y-auto px-5 py-4">
+    <AutoFollowViewport
+      key={autoFollowResetKey}
+      followKey={autoFollowKey}
+    >
       <div className="flex flex-col gap-4">
         <AutoTestTimeline
           startup={startup}
@@ -424,7 +523,7 @@ export function AutoTestLivePanel({
           </div>
         )}
       </div>
-    </div>
+    </AutoFollowViewport>
   );
 }