diff --git a/static/src/components/chat/ChatArea.vue b/static/src/components/chat/ChatArea.vue
index 39a0994..ecb4077 100644
--- a/static/src/components/chat/ChatArea.vue
+++ b/static/src/components/chat/ChatArea.vue
@@ -108,6 +108,7 @@
               :render-markdown="renderMarkdown"
               :register-thinking-ref="registerThinkingRef"
               :handle-thinking-scroll="props.handleThinkingScroll"
+              @group-toggle="handleMinimalGroupToggle"
             />
           </template>
           <template v-else-if="stackedBlocksEnabled">
@@ -154,6 +155,7 @@
                       group.action.blockId || `${index}-thinking-${group.actionIndex}`
                     )
                   }"
+                  :data-block-id="group.action.blockId || `${index}-thinking-${group.actionIndex}`"
                 >
                   <div
                     class="collapsible-header"
@@ -345,6 +347,7 @@
                   :streaming-message="streamingMessage"
                   :register-collapse-content="registerCollapseContent"
                   :collapse-key="group.action.blockId || `${index}-tool-${group.actionIndex}`"
+                  :block-id="group.action.blockId || `${index}-tool-${group.actionIndex}`"
                   @toggle="
                     toggleBlock(group.action.blockId || `${index}-tool-${group.actionIndex}`)
                   "
@@ -378,6 +381,7 @@
                       action.blockId || `${index}-thinking-${actionIndex}`
                     )
                   }"
+                  :data-block-id="action.blockId || `${index}-thinking-${actionIndex}`"
                 >
                   <div
                     class="collapsible-header"
@@ -551,6 +555,7 @@
                   :streaming-message="streamingMessage"
                   :register-collapse-content="registerCollapseContent"
                   :collapse-key="action.blockId || `${index}-tool-${actionIndex}`"
+                  :block-id="action.blockId || `${index}-tool-${actionIndex}`"
                   @toggle="toggleBlock(action.blockId || `${index}-tool-${actionIndex}`)"
                 />
               </div>
@@ -572,6 +577,7 @@
           <div
             class="collapsible-block system-block"
             :class="{ expanded: expandedBlocks?.has(`system-${index}`) }"
+            :data-block-id="`system-${index}`"
           >
             <div class="collapsible-header" @click="toggleBlock(`system-${index}`)">
               <div class="arrow"></div>
@@ -603,6 +609,7 @@
 <script setup lang="ts">
 import { computed, onBeforeUnmount, onMounted, ref, watch } from 'vue';
 import { useStickToBottom } from 'vue-stick-to-bottom';
+import { useBlockExpansionAnchor } from '@/composables/useBlockExpansionAnchor';
 import ToolAction from '@/components/chat/actions/ToolAction.vue';
 import StackedBlocks from './StackedBlocks.vue';
 import MinimalBlocks from './MinimalBlocks.vue';
@@ -797,6 +804,10 @@ const {
   initial: 'instant'
 });
 const rootEl = scrollRef;
+const { anchorBlockElement, stopAll: stopBlockExpansionAnchors } = useBlockExpansionAnchor(
+  scrollRef,
+  { stopScroll }
+);
 const thinkingRefs = new Map<string, HTMLElement | null>();
 let scrollbarResizeObserver: ResizeObserver | null = null;
 let bounceTraceCount = 0;
@@ -1059,6 +1070,78 @@ watch(
   },
   { immediate: true }
 );
+
+function escapeBlockSelector(value: string) {
+  if (typeof CSS !== 'undefined' && typeof CSS.escape === 'function') {
+    return CSS.escape(value);
+  }
+  return value.replace(/["\\]/g, '\\$&');
+}
+
+function elementLooksStreaming(el: HTMLElement) {
+  return (
+    el.classList.contains('processing') ||
+    el.classList.contains('running') ||
+    !!el.querySelector('.processing, .running, .thinking-animation')
+  );
+}
+
+const prevExpandedBlocks = ref(new Set<string>());
+
+watch(
+  () => props.expandedBlocks,
+  (newSet, oldSet) => {
+    const prev = oldSet ?? prevExpandedBlocks.value;
+    const all = new Set([...Array.from(newSet), ...Array.from(prev)]);
+    const changed = new Set<string>();
+    for (const id of all) {
+      if (newSet.has(id) !== prev.has(id)) {
+        changed.add(id);
+      }
+    }
+    prevExpandedBlocks.value = new Set(newSet);
+
+    if (changed.size === 0) return;
+    const container = scrollRef.value;
+    if (!container) return;
+
+    for (const id of changed) {
+      const el = container.querySelector(
+        `[data-block-id="${escapeBlockSelector(id)}"]`
+      ) as HTMLElement | null;
+      if (el) {
+        const isExpanding = newSet.has(id);
+        const streaming = elementLooksStreaming(el);
+        anchorBlockElement(el, id, {
+          direction: 'auto',
+          duration: streaming ? 5000 : 260,
+          extendOnGrowth: streaming,
+          phase: isExpanding ? 'expand' : 'collapse'
+        });
+      }
+    }
+  },
+  { flush: 'post' }
+);
+
+function handleMinimalGroupToggle(payload: { groupId: string; expanded: boolean }) {
+  const { groupId, expanded } = payload;
+  const container = scrollRef.value;
+  if (!container) return;
+  const el = container.querySelector(
+    `[data-group-id="${escapeBlockSelector(groupId)}"]`
+  ) as HTMLElement | null;
+  if (el) {
+    const streaming = elementLooksStreaming(el);
+    anchorBlockElement(el, groupId, {
+      direction: 'auto',
+      duration: streaming ? 5000 : 300,
+      extendOnGrowth: streaming,
+      phase: expanded ? 'expand' : 'collapse'
+    });
+  }
+}
+
 const registerCollapseContent = (key: string, el: Element | null) => {
   if (!(el instanceof HTMLElement)) {
     return;
@@ -1530,6 +1613,7 @@ watch(scrollRef, () => {
 
 onBeforeUnmount(() => {
   detachBounceListener();
+  stopBlockExpansionAnchors();
   if (scrollbarResizeObserver) {
     scrollbarResizeObserver.disconnect();
     scrollbarResizeObserver = null;
diff --git a/static/src/components/chat/MinimalBlocks.vue b/static/src/components/chat/MinimalBlocks.vue
index e4ffc05..9ec8b43 100644
--- a/static/src/components/chat/MinimalBlocks.vue
+++ b/static/src/components/chat/MinimalBlocks.vue
@@ -8,6 +8,7 @@
         <div
           class="summary-line-text"
           :class="{ running: isSummaryRunning(group.actions, group.id) }"
+          :data-group-id="group.id"
           @click="toggleExpand(group.id)"
         >
           <div class="summary-content-wrapper">
@@ -200,6 +201,10 @@ const props = defineProps<{
   handleThinkingScroll?: (blockId: string, event: Event) => void;
 }>();
 
+const emit = defineEmits<{
+  (event: 'group-toggle', payload: { groupId: string; expanded: boolean }): void;
+}>();
+
 const personalizationStore = usePersonalizationStore();
 const expandedGroups = ref(new Set<string>());
 const thinkingRefs = new Map<string, HTMLElement>();
@@ -672,6 +677,7 @@ const getSummarySteps = (actions: Action[]) => {
 const toggleExpand = (groupId: string) => {
   if (expandedGroups.value.has(groupId)) {
     expandedGroups.value.delete(groupId);
+    emit('group-toggle', { groupId, expanded: false });
 
     // 折叠后，取消注册该组中的思考内容 ref
     nextTick(() => {
@@ -689,6 +695,7 @@ const toggleExpand = (groupId: string) => {
     });
   } else {
     expandedGroups.value.add(groupId);
+    emit('group-toggle', { groupId, expanded: true });
 
     // 展开后，注册该组中的思考内容 ref
     nextTick(() => {
diff --git a/static/src/components/chat/StackedBlocks.vue b/static/src/components/chat/StackedBlocks.vue
index ef30334..37bb04e 100644
--- a/static/src/components/chat/StackedBlocks.vue
+++ b/static/src/components/chat/StackedBlocks.vue
@@ -41,6 +41,7 @@
             v-if="action.type === 'thinking'"
             class="collapsible-block thinking-block stacked-block"
             :class="{ expanded: isExpanded(action, idx), processing: action.streaming }"
+            :data-block-id="blockKey(action, idx)"
           >
             <div class="collapsible-header" @click="toggleBlock(blockKey(action, idx))">
               <div class="arrow"></div>
@@ -71,6 +72,7 @@
               processing: isToolProcessing(action),
               completed: isToolCompleted(action)
             }"
+            :data-block-id="blockKey(action, idx)"
           >
             <div class="collapsible-header" @click="toggleBlock(blockKey(action, idx))">
               <div class="arrow"></div>
diff --git a/static/src/components/chat/actions/ToolAction.vue b/static/src/components/chat/actions/ToolAction.vue
index 6bf16d7..5e6696b 100644
--- a/static/src/components/chat/actions/ToolAction.vue
+++ b/static/src/components/chat/actions/ToolAction.vue
@@ -6,6 +6,7 @@
       processing: action.tool.status === 'preparing' || action.tool.status === 'running',
       completed: action.tool.status === 'completed'
     }"
+    :data-block-id="blockId || collapseKey || action.tool.id || action.id || 'tool'"
   >
     <div class="collapsible-header" @click="$emit('toggle')">
       <div class="arrow"></div>
@@ -51,6 +52,7 @@ defineOptions({ name: 'ToolAction' });
 const props = defineProps<{
   action: any;
   expanded: boolean;
+  blockId?: string;
   iconStyle: (key: string) => Record<string, string>;
   getToolAnimationClass: (tool: any) => Record<string, unknown>;
   getToolIcon: (tool: any) => string;
diff --git a/static/src/composables/useBlockExpansionAnchor.ts b/static/src/composables/useBlockExpansionAnchor.ts
new file mode 100644
index 0000000..9ed64ac
--- /dev/null
+++ b/static/src/composables/useBlockExpansionAnchor.ts
@@ -0,0 +1,183 @@
+import { type Ref } from 'vue';
+
+export type BlockExpandDirection = 'auto' | 'up' | 'down';
+
+interface AnchorAnimation {
+  element: HTMLElement;
+  startTime: number;
+  duration: number;
+  mode: 'up' | 'down';
+  initialTop: number;
+  initialBottom: number;
+  extendOnGrowth: boolean;
+  phase: 'expand' | 'collapse';
+}
+
+interface UseBlockExpansionAnchorOptions {
+  stopScroll: () => void;
+  duration?: number;
+  defaultDirection?: BlockExpandDirection;
+}
+
+/**
+ * 块展开/折叠时，以块的某条边为锚点保持视口位置稳定。
+ *
+ * 传统 stick-to-bottom 在内容高度变化时会用弹簧动画追底，和 CSS 展开动画不同步，
+ * 产生顿挫。该 composable 在 CSS 过渡期间用 rAF 持续覆盖 scrollTop。
+ *
+ * 方向策略：
+ * - 展开时根据块顶边在视口的位置决定：上半向下展开（顶边不动），下半向上展开（底边不动）。
+ * - 该方向在本次展开-收起周期内保持一致，确保收起是展开的倒放。
+ * - 收起动画结束后清除方向记录，下次展开再根据新位置重新判断。
+ */
+export function useBlockExpansionAnchor(
+  scrollRef: Ref<HTMLElement | null>,
+  options: UseBlockExpansionAnchorOptions
+) {
+  const { stopScroll, duration = 300, defaultDirection = 'auto' } = options;
+  const animations = new Map<string, AnchorAnimation>();
+  const preferredModes = new Map<string, 'up' | 'down'>();
+  let rafId: number | null = null;
+
+  function resolveMode(rect: DOMRect, containerRect: DOMRect, direction: BlockExpandDirection) {
+    if (direction !== 'auto') return direction;
+    const top = rect.top - containerRect.top;
+    const midY = containerRect.height / 2;
+    return top > midY ? 'up' : 'down';
+  }
+
+  function tick() {
+    const container = scrollRef.value;
+    if (!container) {
+      rafId = null;
+      return;
+    }
+
+    const containerRect = container.getBoundingClientRect();
+    const now = performance.now();
+    let hasActive = false;
+
+    for (const [id, anim] of animations) {
+      const elapsed = now - anim.startTime;
+      const stillInDom =
+        document.body.contains(container) && container.contains(anim.element);
+      if (!stillInDom) {
+        animations.delete(id);
+        continue;
+      }
+
+      const rect = anim.element.getBoundingClientRect();
+      const currentTop = rect.top - containerRect.top;
+      const currentBottom = rect.bottom - containerRect.top;
+
+      let delta = 0;
+      if (anim.mode === 'up') {
+        delta = currentBottom - anim.initialBottom;
+      } else {
+        delta = -(currentTop - anim.initialTop);
+      }
+
+      const stillGrowing = Math.abs(delta) > 1;
+      const shouldExtend = anim.extendOnGrowth && stillGrowing && elapsed > anim.duration * 0.6;
+      if (shouldExtend) {
+        anim.startTime = now - anim.duration * 0.3;
+      }
+
+      if (elapsed >= anim.duration && !shouldExtend) {
+        // 收起动画结束后清除方向记录，下次展开按新位置重新判断
+        if (anim.phase === 'collapse') {
+          preferredModes.delete(id);
+        }
+        animations.delete(id);
+        continue;
+      }
+
+      hasActive = true;
+
+      if (Math.abs(delta) > 0.5) {
+        container.scrollTop += delta;
+      }
+    }
+
+    if (hasActive) {
+      rafId = requestAnimationFrame(tick);
+    } else {
+      rafId = null;
+    }
+  }
+
+  function anchorBlockElement(
+    element: HTMLElement,
+    id: string,
+    opts?: {
+      duration?: number;
+      direction?: BlockExpandDirection;
+      extendOnGrowth?: boolean;
+      phase?: 'expand' | 'collapse';
+    }
+  ) {
+    const container = scrollRef.value;
+    if (!container) return;
+
+    const containerRect = container.getBoundingClientRect();
+    const rect = element.getBoundingClientRect();
+    const initialTop = rect.top - containerRect.top;
+    const initialBottom = rect.bottom - containerRect.top;
+
+    // 只处理视口附近可见的块
+    if (initialBottom < -50 || initialTop > containerRect.height + 50) {
+      return;
+    }
+
+    const phase = opts?.phase ?? 'expand';
+    const explicitDirection = opts?.direction ?? defaultDirection;
+    let mode: 'up' | 'down';
+
+    if (explicitDirection !== 'auto') {
+      mode = explicitDirection;
+    } else if (phase === 'collapse' && preferredModes.has(id)) {
+      // 收起时沿用展开时记录的方向，保证倒放一致
+      mode = preferredModes.get(id)!;
+    } else if (phase === 'expand' && preferredModes.has(id)) {
+      // 同一次周期内再次展开（不应常见），沿用已有方向
+      mode = preferredModes.get(id)!;
+    } else {
+      mode = resolveMode(rect, containerRect, 'auto');
+      preferredModes.set(id, mode);
+    }
+
+    const extendOnGrowth = opts?.extendOnGrowth ?? false;
+
+    stopScroll();
+
+    const existing = animations.get(id);
+    animations.set(id, {
+      element,
+      startTime: performance.now(),
+      duration: opts?.duration ?? duration,
+      mode,
+      initialTop,
+      initialBottom,
+      extendOnGrowth: extendOnGrowth || existing?.extendOnGrowth || false,
+      phase
+    });
+
+    if (rafId === null) {
+      rafId = requestAnimationFrame(tick);
+    }
+  }
+
+  function stopAll() {
+    if (rafId !== null) {
+      cancelAnimationFrame(rafId);
+      rafId = null;
+    }
+    animations.clear();
+    preferredModes.clear();
+  }
+
+  return {
+    anchorBlockElement,
+    stopAll
+  };
+}