fix(web): 无用户行钉顶、闲置不上留白，并修会话列表 tsc 两错

frontend/src/hooks/use-conversation-scroll-anchor.ts

@@ -76,9 +76,26 @@ export function applyFollowBottom(
   element.scrollTop = element.scrollHeight;
 }
 
+export function lastTurnTail(container: HTMLElement): HTMLElement | null {
+  return (container.querySelector(".message-list > :last-child .message-assistant")
+    ?? container.querySelector(".message-assistant:last-of-type")
+    ?? container.querySelector(".message-user:last-of-type")) as HTMLElement | null;
+}
+
+export function turnHeadHeightForSpacer(head: HTMLElement | null, tail: HTMLElement | null): number {
+  if (!head) return 0;
+  // The last assistant carries the min-height spacer. Measuring it as the turn
+  // head feeds the spacer back into itself (BUG-931).
+  if (tail && head === tail) return 0;
+  return head.offsetHeight;
+}
+
 export function applyTurnSpacer(container: HTMLElement, head: HTMLElement | null): void {
   container.style.setProperty("--conversation-viewport", `${container.clientHeight}px`);
-  container.style.setProperty("--latest-turn-head-height", `${head?.offsetHeight ?? 0}px`);
+  container.style.setProperty(
+    "--latest-turn-head-height",
+    `${turnHeadHeightForSpacer(head, lastTurnTail(container))}px`,
+  );
 }
 
 export function clearTurnSpacer(container: HTMLElement): void {
@@ -86,12 +103,6 @@ export function clearTurnSpacer(container: HTMLElement): void {
   container.style.removeProperty("--latest-turn-head-height");
 }
 
-export function lastTurnTail(container: HTMLElement): HTMLElement | null {
-  return (container.querySelector(".message-list > :last-child .message-assistant")
-    ?? container.querySelector(".message-assistant:last-of-type")
-    ?? container.querySelector(".message-user:last-of-type")) as HTMLElement | null;
-}
-
 export function turnTailOverflow(container: HTMLElement): number {
   const last = lastTurnTail(container);
   if (!last) return conversationDistanceFromBottom(container);
@@ -198,8 +209,8 @@ export function useConversationScrollAnchor(
       }
       if (anchoredRef.current) {
         element.scrollTop = element.scrollHeight;
-      } else {
-        applyTurnSpacer(element, pinnedHeadRef.current ?? resolveTurnHead(element));
+      } else if (pinnedHeadRef.current) {
+        applyTurnSpacer(element, pinnedHeadRef.current);
       }
       setLatestBelowFold(latestContentBelowFold(turnTailOverflow(element)));
     };
@@ -240,7 +251,9 @@ export function useConversationScrollAnchor(
       const element = container.current;
       holdUnpin.current = false;
       shouldLand.current = false;
+      pinnedHeadRef.current = null;
       if (element) {
+        clearTurnSpacer(element);
         const reduceMotion = window.matchMedia("(prefers-reduced-motion: reduce)").matches;
         element.scrollTo({ top: element.scrollHeight, behavior: reduceMotion ? "auto" : "smooth" });
         setLatestBelowFold(false);

frontend/src/lib/session-sidebar-row.ts

@@ -27,7 +27,7 @@ export function toSidebarSessionRow(
 ): SidebarSession {
   return {
     id: session.id,
-    title: sessionSidebarTitle(session, library),
+    title: sessionSidebarTitle(session),
     subtitle: sessionSidebarSubtitle(session, library) || null,
     pinned: session.pinned,
     archived: Boolean(session.archivedAt),

frontend/tests/chart-library-session.test.ts

@@ -86,7 +86,10 @@ test("sidebar titles drop the chart-name prefix and only subtitle others", () =>
     archivedAt: null,
     messagesHydrated: true,
   };
-  assert.equal(sessionSidebarTitle(base, library), "半年内换工作时机");
+  // 原值: sessionSidebarTitle(base, library)
+  // 新值: sessionSidebarTitle(base)
+  // 原因: sessionSidebarTitle 只吃 session；第二参是 e4e73f56 的 TS 错，挡住 tsc / next build
+  assert.equal(sessionSidebarTitle(base), "半年内换工作时机");
   assert.equal(sessionSidebarSubtitle(base, library), "9月14日 12:14");
   const other = { ...base, chartProfileId: "other-1", chartProfileName: "对方", chartProfileRole: "other" as const };
   assert.equal(sessionSidebarSubtitle(other, library), "9月14日 12:14 · 资料已删除 · 对方");

frontend/tests/chat-notice-and-scroll-contract.test.ts

@@ -235,6 +235,49 @@ test("turn spacer uses conversation viewport variables and is not sticky", () =>
   assert.equal(scroller.style.getPropertyValue("--latest-turn-head-height"), "");
 });
 
+test("a turn with no user row pins the new assistant and uses a full-viewport spacer", () => {
+  const priorUser = fakeRow("message-user", 8, 40);
+  const priorAssistant = fakeRow("message-assistant", 56, 80);
+  const laterUser = fakeRow("message-user", 152, 40);
+  const laterAssistant = fakeRow("message-assistant", 200, 80);
+  const incoming = fakeRow("message-assistant", 480, 80);
+  const scroller = fakeScroller([priorUser, priorAssistant, laterUser, laterAssistant, incoming], 600);
+  const head = resolveTurnHead(asElement(scroller));
+  assert.equal(head, asElement(incoming));
+  applyTurnSpacer(asElement(scroller), head);
+  assert.equal(scroller.style.getPropertyValue("--latest-turn-head-height"), "0px");
+  scroller.scrollTop = pinTurnScrollTop(asElement(scroller), asElement(incoming), 16);
+  assert.equal(scroller.scrollTop, incoming.offsetTop - 16);
+  const start = scroller.scrollTop;
+  for (let i = 0; i < 3; i += 1) {
+    incoming.offsetHeight += 80;
+    scroller.scrollHeight += 80;
+    applyFollowBottom(scroller, false);
+  }
+  assert.equal(scroller.scrollTop, start);
+});
+
+test("idle history does not write a spacer when the reader has only scrolled up", () => {
+  // 原值: follow() 在 !anchored 时无条件 applyTurnSpacer
+  // 新值: 只在 pinnedHeadRef 非空时写留白
+  // 原因: BUG-932 闲置会话上滑后子元素尺寸变化不应把最后一条助手行撑开
+  assert.match(
+    anchorSource,
+    /if \(anchoredRef\.current\) \{\s*element\.scrollTop = element\.scrollHeight;\s*\} else if \(pinnedHeadRef\.current\) \{\s*applyTurnSpacer\(element, pinnedHeadRef\.current\);/,
+  );
+  assert.match(anchorSource, /pinnedHeadRef\.current = null;\s*if \(element\) \{\s*clearTurnSpacer\(element\);/);
+  const user = fakeRow("message-user", 8, 40);
+  const assistant = fakeRow("message-assistant", 56, 900);
+  const scroller = fakeScroller([user, assistant], 600);
+  scroller.scrollTop = scroller.scrollHeight - scroller.clientHeight;
+  scroller.scrollTop = Math.max(0, scroller.scrollTop - 400);
+  const start = scroller.scrollTop;
+  assistant.offsetHeight += 30;
+  scroller.scrollHeight += 30;
+  assert.equal(scroller.style.getPropertyValue("--conversation-viewport"), "");
+  assert.equal(Math.abs(scroller.scrollTop - start) <= 1, true);
+});
+
 test("consultation send and rectification new turns call pinLatestTurn", () => {
   const chat = readFileSync(new URL("../src/components/rectification-agentic-chat.tsx", import.meta.url), "utf8");
   const pins = chat.match(/conversationAnchor\.pinLatestTurn\(\)/g) ?? [];