diff --git a/src/components/trace/TraceViewer.tsx b/src/components/trace/TraceViewer.tsx
index 72604ac..f0ff1ce 100644
--- a/src/components/trace/TraceViewer.tsx
+++ b/src/components/trace/TraceViewer.tsx
@@ -1,17 +1,70 @@
 /**
  * TraceViewer — ReAct 迭代追踪时间轴
  *
+ * 方案 A+: 按 runId 分组渲染，每轮 AI 回复一个独立 section
+ * - 所有历史 run 的 steps 都可见
+ * - 每个 run 视觉分离（带标题"第 N 轮"+ 状态徽标）
+ * - 当前 run 高亮显示
+ *
  * flex:1 撑满详情面板剩余空间，内容超出时内部滚动。
  */
 
-import { Box, Typography, Stack } from '@mui/material';
-import { Activity } from 'lucide-react';
+import { Box, Typography, Stack, Chip } from '@mui/material';
+import { Activity, MessageSquare } from 'lucide-react';
+import { useMemo } from 'react';
 import { useAgentStore } from '@renderer/stores/agent-store';
+import type { TraceStep as TraceStepType } from '@renderer/stores/agent-store';
 import { TraceStep } from './TraceStep';
 
+interface RunGroup {
+  runId: string;
+  index: number;       // 1-based 轮次序号
+  steps: TraceStepType[];
+  isCurrent: boolean;  // 是否为当前正在进行的 run
+  isCompleted: boolean; // 是否已完成（最后一个 step 有 completedAt）
+}
+
+function groupByRun(traceSteps: TraceStepType[], currentRunId: string | null): RunGroup[] {
+  const runOrder: string[] = [];
+  const runMap = new Map<string, TraceStepType[]>();
+
+  for (const step of traceSteps) {
+    const rid = step.runId;
+    if (!rid) continue;
+    if (!runMap.has(rid)) {
+      runMap.set(rid, []);
+      runOrder.push(rid);
+    }
+    runMap.get(rid)!.push(step);
+  }
+
+  // 当前 runId 优先；若为空（idle）则取最后一个 run 作为"当前展示"
+  const effectiveCurrentRunId = currentRunId ?? (runOrder.length > 0 ? runOrder[runOrder.length - 1] : null);
+
+  return runOrder.map((rid, i) => {
+    const steps = runMap.get(rid)!;
+    const lastStep = steps[steps.length - 1];
+    return {
+      runId: rid,
+      index: i + 1,
+      steps,
+      isCurrent: rid === effectiveCurrentRunId,
+      isCompleted: Boolean(lastStep?.completedAt),
+    };
+  });
+}
+
 export function TraceViewer(): React.JSX.Element {
-  const traceSteps = useAgentStore((s) => s.traceSteps);
+  const allTraceSteps = useAgentStore((s) => s.traceSteps);
   const agentStatus = useAgentStore((s) => s.agentStatus);
+  const currentRunId = useAgentStore((s) => s.currentRunId);
+
+  const groups = useMemo(
+    () => groupByRun(allTraceSteps, currentRunId),
+    [allTraceSteps, currentRunId],
+  );
+
+  const isEmpty = groups.length === 0;
 
   return (
     <Box sx={{ flex: 1, display: 'flex', flexDirection: 'column', minHeight: 0, overflow: 'hidden' }}>
@@ -20,20 +73,79 @@ export function TraceViewer(): React.JSX.Element {
         <Typography variant="caption" sx={{ fontWeight: 600, textTransform: 'uppercase', letterSpacing: 1, color: 'text.secondary' }}>
           Trace Viewer
         </Typography>
+        {!isEmpty && (
+          <Typography variant="caption" sx={{ color: 'text.disabled', ml: 'auto' }}>
+            共 {groups.length} 轮
+          </Typography>
+        )}
       </Stack>
 
-      <Box sx={{ flex: 1, overflowY: 'auto', display: 'flex', flexDirection: 'column', gap: 0.5, minHeight: 0 }}>
-        {traceSteps.length === 0 ? (
+      <Box sx={{ flex: 1, overflowY: 'auto', display: 'flex', flexDirection: 'column', gap: 1.5, minHeight: 0 }}>
+        {isEmpty ? (
           <Typography variant="caption" sx={{ textAlign: 'center', py: 2, color: 'text.disabled', flex: 1, display: 'flex', alignItems: 'center', justifyContent: 'center' }}>
             等待 Agent 活动...
           </Typography>
         ) : (
-          traceSteps.map((step, i) => (
-            <TraceStep
-              key={step.id}
-              step={step}
-              isCurrent={i === traceSteps.length - 1 && agentStatus !== 'idle'}
-            />
+          groups.map((group) => (
+            <Box
+              key={group.runId}
+              sx={{
+                border: 1,
+                borderColor: group.isCurrent ? 'primary.main' : 'divider',
+                borderRadius: 1,
+                p: 1,
+                bgcolor: group.isCurrent ? 'action.hover' : 'transparent',
+                opacity: group.isCurrent ? 1 : 0.85,
+              }}
+            >
+              <Stack
+                direction="row"
+                spacing={1}
+                sx={{ mb: 1, alignItems: 'center', flexShrink: 0 }}
+              >
+                <MessageSquare size={12} style={{ color: group.isCurrent ? '#818cf8' : '#9ca3af' }} />
+                <Typography
+                  variant="caption"
+                  sx={{
+                    fontWeight: 600,
+                    color: group.isCurrent ? 'primary.main' : 'text.secondary',
+                    letterSpacing: 0.5,
+                  }}
+                >
+                  第 {group.index} 轮
+                </Typography>
+                {group.isCurrent && agentStatus !== 'idle' && (
+                  <Chip
+                    label="进行中"
+                    size="small"
+                    color="primary"
+                    variant="outlined"
+                    sx={{ height: 16, fontSize: 10, '& .MuiChip-label': { px: 0.5 } }}
+                  />
+                )}
+                {group.isCompleted && !group.isCurrent && (
+                  <Chip
+                    label="已完成"
+                    size="small"
+                    variant="outlined"
+                    sx={{ height: 16, fontSize: 10, '& .MuiChip-label': { px: 0.5 }, color: 'text.disabled' }}
+                  />
+                )}
+                <Typography variant="caption" sx={{ ml: 'auto', color: 'text.disabled', fontSize: 10 }}>
+                  {group.steps.length} 步
+                </Typography>
+              </Stack>
+
+              <Box sx={{ display: 'flex', flexDirection: 'column', gap: 0.5 }}>
+                {group.steps.map((step, i) => (
+                  <TraceStep
+                    key={step.id}
+                    step={step}
+                    isCurrent={group.isCurrent && i === group.steps.length - 1 && agentStatus !== 'idle'}
+                  />
+                ))}
+              </Box>
+            </Box>
           ))
         )}
       </Box>
diff --git a/src/stores/agent-store.ts b/src/stores/agent-store.ts
index 5fb6719..a1ed7bc 100644
--- a/src/stores/agent-store.ts
+++ b/src/stores/agent-store.ts
@@ -267,9 +267,9 @@ export const useAgentStore = create<AgentState>((set, get) => ({
       isStreaming: true,
       currentRunId: null, // 将在首个 streamEvent 中由 runId 设置
       currentIteration: 0,
-      // 重置 trace 状态：防止新消息在上一条消息的 trace 上面叠加渲染
-      // 前一条消息的 trace 已在 done 事件中通过 saveTraceData() 持久化到 DB
-      traceSteps: [],
+      // 方案 A: 不清空 traceSteps，避免前一条消息的 trace 被永久覆盖
+      // TraceViewer 按 runId 过滤显示，只展示当前 run 的 steps
+      // 历史 trace 仍在 DB 中，切换会话回来可恢复
       tokenUsage: { inputTokens: 0, outputTokens: 0, totalTokens: 0 },
     }));