fix trace scroll preservation

docs/reference/cloud-workbench.md

@@ -108,6 +108,12 @@ session identifiers, the visible detail must include a short redacted
 [Code Agent readiness](code-agent-chat-readiness.md) 合同返回 completed
 且非空的 assistant response 前，Workbench 不得暗示已有真实 assistant reply。
 
+Code Agent trace 在消息卡片内使用独立滚动容器展示。SSE、轮询或“回放 trace”
+更新只能刷新内容，不得重置用户已展开/折叠状态，也不得把
+`.message-trace-events` 的内部滚动位置跳回顶部；渲染前后必须按
+`messageId/traceId` 保存并恢复 trace list 的 `scrollTop/scrollLeft`。完整 trace
+可通过复制/下载获取，页面内默认保持“显示全部 + 内部滚动”的单一模式。
+
 ## Lightweight Checks
 
 Use the existing lightweight checks unless a task explicitly authorizes a

web/hwlab-cloud-web/app.mjs

@@ -180,6 +180,7 @@ const state = {
   chatMessages: [],
   traceStreams: new Map(),
   traceDetailsOpen: new Map(),
+  traceScrollPositions: new Map(),
   canceledTraces: new Set(),
   currentRequest: null,
   sessionStatus: null,
@@ -791,6 +792,7 @@ function initCommandBar() {
     for (const close of state.traceStreams.values()) close();
     state.traceStreams.clear();
     state.traceDetailsOpen.clear();
+    state.traceScrollPositions.clear();
     state.chatMessages = [];
     state.conversationId = null;
     state.sessionId = null;
@@ -2004,6 +2006,7 @@ function workbenchApiSurfaceStatus(live, coreProbes = [live.healthLive, live.res
 }
 
 function renderConversation() {
+  captureTraceScrollPositions();
   const introMessages = [
     {
       role: "system",
@@ -2014,6 +2017,30 @@ function renderConversation() {
     codeAgentStatusMessage(state.codeAgentAvailability)
   ];
   replaceChildren(el.conversationList, ...[...introMessages, ...state.chatMessages].map(messageCard));
+  restoreTraceScrollPositions();
+}
+
+function captureTraceScrollPositions(root = el.conversationList) {
+  for (const list of root.querySelectorAll(".message-trace-events[data-trace-ui-key]")) {
+    rememberTraceScrollPosition(list.dataset.traceUiKey, list);
+  }
+}
+
+function rememberTraceScrollPosition(traceUiKey, list) {
+  if (!traceUiKey || !list) return;
+  state.traceScrollPositions.set(traceUiKey, {
+    top: list.scrollTop,
+    left: list.scrollLeft
+  });
+}
+
+function restoreTraceScrollPositions(root = el.conversationList) {
+  for (const list of root.querySelectorAll(".message-trace-events[data-trace-ui-key]")) {
+    const position = state.traceScrollPositions.get(list.dataset.traceUiKey);
+    if (!position) continue;
+    list.scrollTop = Math.min(position.top, Math.max(0, list.scrollHeight - list.clientHeight));
+    list.scrollLeft = Math.min(position.left, Math.max(0, list.scrollWidth - list.clientWidth));
+  }
 }
 
 function renderHardwareStatus(m3Status) {
@@ -4066,6 +4093,10 @@ function messageTracePanel(message) {
   summary.textContent = runnerTraceHeadline(message, trace);
   const list = document.createElement("ol");
   list.className = "message-trace-events";
+  if (traceUiKey) {
+    list.dataset.traceUiKey = traceUiKey;
+    list.addEventListener("scroll", () => rememberTraceScrollPosition(traceUiKey, list), { passive: true });
+  }
   const events = Array.isArray(trace?.events) ? trace.events : [];
   const rows = traceDisplayRows(trace, events);
   if (events.length === 0) {

web/hwlab-cloud-web/scripts/check.mjs

@@ -809,12 +809,21 @@ assert.match(app, /function messageTraceToolbar/);
 assert.match(app, /function messageTraceCountText/);
 assert.match(app, /显示全部\s+\$\{displayTotal\}\s+\/\s+原始\s+\$\{rawTotal\}/);
 assert.match(app, /traceDetailsOpen:\s*new Map\(\)/);
+assert.match(app, /traceScrollPositions:\s*new Map\(\)/);
 assert.match(app, /state\.traceDetailsOpen\.clear\(\)/);
+assert.match(app, /state\.traceScrollPositions\.clear\(\)/);
 assert.match(app, /function messageTraceUiKey/);
 assert.match(app, /function defaultTraceDetailsOpen/);
+assert.match(app, /function captureTraceScrollPositions/);
+assert.match(app, /function restoreTraceScrollPositions/);
+assert.match(app, /function rememberTraceScrollPosition/);
+assert.match(functionBody(app, "renderConversation"), /captureTraceScrollPositions\(\)/);
+assert.match(functionBody(app, "renderConversation"), /restoreTraceScrollPositions\(\)/);
 assert.match(functionBody(app, "messageTracePanel"), /state\.traceDetailsOpen\.get\(traceUiKey\)/);
 assert.match(functionBody(app, "messageTracePanel"), /defaultTraceDetailsOpen\(message\)/);
 assert.match(functionBody(app, "messageTracePanel"), /state\.traceDetailsOpen\.set\(traceUiKey,\s*details\.open\)/);
+assert.match(functionBody(app, "messageTracePanel"), /list\.dataset\.traceUiKey\s*=\s*traceUiKey/);
+assert.match(functionBody(app, "messageTracePanel"), /rememberTraceScrollPosition\(traceUiKey,\s*list\)/);
 assert.match(functionBody(app, "messageTracePanel"), /list\.dataset\.traceMode\s*=\s*"all"/);
 assert.match(functionBody(app, "messageTracePanel"), /renderTraceEventList\(list,\s*rows\)/);
 assert.doesNotMatch(app, /CODE_AGENT_TRACE_PREVIEW_LIMIT|tracePreviewRows|收起为最近|展开全部|data-trace-mode="tail"/);