diff --git a/electron/board-store.ts b/electron/board-store.ts
index 94ecea0..2e3b503 100644
--- a/electron/board-store.ts
+++ b/electron/board-store.ts
@@ -161,6 +161,7 @@ export class BoardStore {
         result.push({
           id: board.id,
           title: board.title,
+          sessionCount: board.sessionCount,
           kind: board.kind,
           updatedAt: board.updatedAt,
           ...(board.archivedAt ? { archivedAt: board.archivedAt } : {}),
diff --git a/src/App.tsx b/src/App.tsx
index 5bc8482..a7bf99e 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -1630,18 +1630,36 @@ export default function App() {
     boardId: string,
     sessionId: string,
   ): Promise<void> {
-    if (locked()) return;
+    if (locked()) throw new Error("正在切换画布");
     if (boardRef.current?.id !== boardId) await switchBoard(boardId);
     const current = boardRef.current;
-    if (current?.id !== boardId) return;
+    if (current?.id !== boardId) throw new Error("无法打开画布");
     const target = current.notes.find((note) => note.id === sessionId);
-    if (!target) return;
+    if (!target) throw new Error("对话不存在");
     openDrawer(sessionId);
     const at = target.attachedTo;
-    if (at) setSelection(at);
-    if (at?.kind === "node") {
+    const anchorExists =
+      at?.kind === "node"
+        ? current.nodes.some((n) => n.id === at.id)
+        : at?.kind === "relation"
+          ? current.relations.some((r) => r.id === at.id)
+          : false;
+    if (at && anchorExists) setSelection(at);
+    if (at && !anchorExists) {
+      setSelection(null);
+      setTimeout(() => flow.fitView({ padding: 0.16, duration: 400 }), 80);
+      showToast("锚点卡已不在画布上");
+    }
+    if (at?.kind === "node" && anchorExists) {
       // Let React Flow render the selected board before locating its card.
       setTimeout(() => frameFamily(at.id, true), 80);
+    } else if (at?.kind === "relation" && anchorExists) {
+      const relation = current.relations.find((r) => r.id === at.id)!;
+      setTimeout(() => flow.fitView({
+        nodes: [{ id: relation.source }, { id: relation.target }],
+        padding: 0.2,
+        duration: 320,
+      }), 80);
     }
   }
   async function createBoard(walkthrough = false) {
@@ -3017,7 +3035,7 @@ export default function App() {
               sessions={listSessions(board)}
               currentSessionId={drawer?.id}
               onOpenSession={(boardId, sessionId) =>
-                void openSession(boardId, sessionId)
+                openSession(boardId, sessionId)
               }
               onNewSession={() => addNote(undefined, { fresh: true })}
             />
diff --git a/src/api.ts b/src/api.ts
index 9b2f7d7..78421c8 100644
--- a/src/api.ts
+++ b/src/api.ts
@@ -39,6 +39,7 @@ const preview: AtlasAPI = {
     return read().map((b) => ({
       id: b.id,
       title: b.title,
+      sessionCount: b.sessionCount,
       kind: b.kind,
       updatedAt: b.updatedAt,
       ...(b.archivedAt ? { archivedAt: b.archivedAt } : {}),
diff --git a/src/components/WorkspaceSidebar.tsx b/src/components/WorkspaceSidebar.tsx
index e8314c9..c4ff0f6 100644
--- a/src/components/WorkspaceSidebar.tsx
+++ b/src/components/WorkspaceSidebar.tsx
@@ -9,6 +9,7 @@ import { createPortal } from "react-dom";
 import {
   Archive,
   ChevronRight,
+  ChevronDown,
   Compass,
   LoaderCircle,
   MessageSquare,
@@ -22,12 +23,16 @@ import type { BoardSummary } from "../shared/types";
 import { api } from "../api";
 import {
   listSessions,
+  visibleSessions,
+  filterSessions,
   sessionClock,
   type SessionEntry,
 } from "../model/sessions";
 import { MOD } from "../model/shortcuts";
 import { tip } from "./Tooltip";
 
+const SESSION_VIEW_KEY = "studyboard.sidebar.sessions.v1";
+
 export const SIDEBAR_DEFAULT_WIDTH = 256;
 export const SIDEBAR_MIN_WIDTH = 200;
 export const SIDEBAR_MAX_WIDTH = 400;
@@ -52,7 +57,7 @@ type WorkspaceSidebarProps = {
   onSettings: () => void;
   sessions: SessionEntry[];
   currentSessionId?: string;
-  onOpenSession: (boardId: string, sessionId: string) => void;
+  onOpenSession: (boardId: string, sessionId: string) => Promise<void>;
   onNewSession: () => void;
 };
 
@@ -65,7 +70,7 @@ type BoardGroupProps = {
   currentSessionId?: string;
   onPick: () => void;
   onContextMenu: (event: React.MouseEvent<HTMLButtonElement>) => void;
-  onOpenSession: (sessionId: string) => void;
+  onOpenSession: (sessionId: string) => Promise<void>;
   onNewSession: () => void;
 };
 
@@ -86,20 +91,79 @@ function BoardGroup({
   onOpenSession,
   onNewSession,
 }: BoardGroupProps): ReactElement {
-  const [expanded, setExpanded] = useState(false);
+  const [view, setView] = useState(() => {
+    try {
+      return (
+        JSON.parse(localStorage.getItem(SESSION_VIEW_KEY) ?? "{}")[
+          board.id
+        ] ?? { open: false, all: false }
+      );
+    } catch {
+      return { open: false, all: false };
+    }
+  });
+  const expanded = view.open === true;
+  function updateView(patch: { open?: boolean; all?: boolean }): void {
+    const next = { ...view, ...patch };
+    setView(next);
+    try {
+      const saved = JSON.parse(localStorage.getItem(SESSION_VIEW_KEY) ?? "{}");
+      localStorage.setItem(
+        SESSION_VIEW_KEY,
+        JSON.stringify({ ...saved, [board.id]: next }),
+      );
+    } catch {
+      /* Storage can be unavailable. */
+    }
+  }
+  const [query, setQuery] = useState("");
+  const [opening, setOpening] = useState<string | null>(null);
+  const [openError, setOpenError] = useState<string | null>(null);
+  const activeRef = useRef<HTMLButtonElement>(null);
+  const cache = useRef<{
+    stamp: string;
+    retry: number;
+    entries: SessionEntry[];
+  } | null>(null);
+  useEffect(() => {
+    if (expanded && currentSessionId && current)
+      activeRef.current?.scrollIntoView({ block: "nearest" });
+  }, [expanded, currentSessionId, current]);
+  async function open(id: string): Promise<void> {
+    if (opening || switchingId) return;
+    setOpening(id);
+    setOpenError(null);
+    try {
+      await onOpenSession(id);
+      updateView({ open: true });
+    } catch {
+      setOpenError(id);
+    } finally {
+      setOpening(null);
+    }
+  }
   const [savedSessions, setSavedSessions] = useState<SessionLoadState>({
     status: "loading",
   });
   const [retry, setRetry] = useState(0);
   useEffect(() => {
     if (current || !expanded || collapsed) return;
+    if (
+      cache.current?.stamp === board.updatedAt &&
+      cache.current.retry === retry
+    ) {
+      setSavedSessions({ status: "ready", entries: cache.current.entries });
+      return;
+    }
     let cancelled = false;
     setSavedSessions({ status: "loading" });
     void api.loadBoard(board.id).then(
       (value) => {
         if (cancelled) return;
         if (value) {
-          setSavedSessions({ status: "ready", entries: listSessions(value) });
+          const entries = listSessions(value);
+          cache.current = { stamp: board.updatedAt, retry, entries };
+          setSavedSessions({ status: "ready", entries });
         } else {
           setSavedSessions({ status: "error", message: "画布不存在" });
         }
@@ -113,55 +177,128 @@ function BoardGroup({
       cancelled = true;
     };
   }, [board.id, board.updatedAt, current, expanded, collapsed, retry]);
+  useEffect(() => {
+    if (current)
+      cache.current = { stamp: board.updatedAt, retry, entries: sessions };
+  }, [current, board.updatedAt, retry, sessions]);
   const sessionState: SessionLoadState = current
     ? { status: "ready", entries: sessions }
     : savedSessions;
-  const disabled = switchingId !== null;
+  const disabled = switchingId !== null || opening !== null;
   const activeSessionId = current ? currentSessionId : undefined;
+  const count = current
+    ? sessions.length
+    : sessionState.status === "ready"
+      ? sessionState.entries.length
+      : board.sessionCount;
+  const filtered =
+    sessionState.status === "ready"
+      ? filterSessions(sessionState.entries, query)
+      : [];
+  const { rows, hidden } = visibleSessions(
+    filtered,
+    activeSessionId,
+    view.all || !!query.trim(),
+  );
+  const disclosureLabel = `${expanded ? "收起" : "展开"}对话（${count ?? "未知"}）`;
   let sessionItems: ReactNode;
   if (sessionState.status === "error") {
     sessionItems = (
       <li className="workspace-empty" role="alert">
-        {sessionState.message}。
+        无法读取对话 ·
         <button onClick={() => setRetry((value) => value + 1)}>重试</button>
       </li>
     );
   } else if (sessionState.status === "loading") {
     sessionItems = (
-      <li className="workspace-empty" role="status">
-        正在读取对话…
+      <li role="status">
+        <div className="workspace-empty">正在读取对话…</div>
+        {Array.from({ length: Math.min(count ?? 3, 3) }, (_, i) => (
+          <div
+            className="workspace-session-skeleton"
+            aria-hidden="true"
+            key={i}
+          >
+            <i />
+            <i />
+          </div>
+        ))}
       </li>
     );
   } else if (!sessionState.entries.length) {
     sessionItems = <li className="workspace-empty">还没有对话</li>;
   } else {
-    sessionItems = sessionState.entries.map((session) => (
-      <li key={session.id}>
-        <button
-          className="workspace-session"
-          title={`${session.title} · ${session.anchorTitle} · ${sessionClock(session.time)}`}
-          aria-current={session.id === activeSessionId ? "true" : undefined}
-          disabled={disabled}
-          onClick={() => onOpenSession(session.id)}
-        >
-          <MessageSquare size={14} className="ico" />
-          <span>{session.title}</span>
-        </button>
-      </li>
-    ));
+    sessionItems = rows.length ? (
+      rows.map((session) => (
+        <li key={session.id} role="none">
+          <button
+            ref={session.id === activeSessionId ? activeRef : undefined}
+            role="treeitem"
+            className="workspace-session"
+            title={`${session.title} · ${session.anchorTitle} · ${sessionClock(session.time)}`}
+            aria-current={session.id === activeSessionId ? "page" : undefined}
+            aria-busy={opening === session.id}
+            disabled={disabled}
+            onClick={() => void open(session.id)}
+          >
+            {opening === session.id && (
+              <span aria-hidden="true" className="workspace-session-spinner spin" />
+            )}
+            <span className="workspace-session-title">{session.title}</span>
+            <span className="workspace-session-meta">
+              <span>{session.anchorTitle || "自由批注"}</span>
+              <time>· {sessionClock(session.time)}</time>
+            </span>
+          </button>
+          {openError === session.id && (
+            <div
+              className="workspace-empty workspace-session-error"
+              role="alert"
+            >
+              无法打开 ·{" "}
+              <button onClick={() => void open(session.id)}>重试</button>
+            </div>
+          )}
+        </li>
+      ))
+    ) : (
+      <li className="workspace-empty">没有匹配的对话</li>
+    );
   }
   return (
-    <li>
-      <div className="workspace-board-row">
+    <li
+      role="treeitem"
+      aria-label={board.title}
+      aria-current={current ? "true" : undefined}
+      aria-expanded={collapsed ? undefined : expanded}
+      onKeyDown={(e) => {
+        if (
+          e.target instanceof HTMLInputElement ||
+          (e.target as HTMLElement).closest(".workspace-sessions")
+        )
+          return;
+        if (e.key === "ArrowRight" || e.key === "ArrowLeft") {
+          e.preventDefault();
+          e.stopPropagation();
+          updateView({ open: e.key === "ArrowRight" });
+        }
+      }}
+    >
+      <div
+        onClick={(e) => {
+          if (!(e.target as HTMLElement).closest("button")) onPick();
+        }}
+        className={`workspace-board-row ${current ? "is-current" : ""} ${count ? "has-sessions" : ""}`}
+      >
         {!collapsed && (
           <button
-            className="workspace-disclosure"
-            aria-label={`${expanded ? "收起" : "展开"}${board.title}的对话`}
+            className={`workspace-disclosure ${count === 0 ? "is-empty" : ""}`}
+            aria-label={disclosureLabel}
             aria-expanded={expanded}
-            aria-controls={`board-sessions-${board.id}`}
-            onClick={() => setExpanded((value) => !value)}
+            aria-controls={`sessions-${board.id}`}
+            onClick={() => updateView({ open: !expanded })}
           >
-            <ChevronRight size={14} />
+            <ChevronRight size={16} />
           </button>
         )}
         <button
@@ -187,13 +324,17 @@ function BoardGroup({
                 <i
                   className="workspace-rail-bar"
                   aria-hidden="true"
-                  style={{ ["--p" as string]: `${Math.round(((board.sealed ?? 0) / board.total) * 100)}%` }}
+                  style={{
+                    ["--p" as string]: `${Math.round(((board.sealed ?? 0) / board.total) * 100)}%`,
+                  }}
                 />
               )}
             </>
           ) : (
             <>
-              <span className="workspace-copy workspace-board-title">{board.title}</span>
+              <span className="workspace-copy workspace-board-title">
+                {board.title}
+              </span>
               <span className="workspace-meta">
                 {board.done ? (
                   <span className="workspace-done">
@@ -220,15 +361,53 @@ function BoardGroup({
             </>
           )}
         </button>
+        {!collapsed && !!count && (
+          <button
+            className={`workspace-session-count ${current && !!currentSessionId && !expanded ? "is-open" : ""}`}
+            aria-label={disclosureLabel}
+            aria-expanded={expanded}
+            aria-controls={`sessions-${board.id}`}
+            onClick={() => updateView({ open: !expanded })}
+          >
+            <MessageSquare size={12} />
+            <span>{count}</span>
+          </button>
+        )}
       </div>
       {!collapsed && (
         <ul
-          id={`board-sessions-${board.id}`}
+          id={`sessions-${board.id}`}
+          role="group"
           className="workspace-sessions"
           aria-label={`${board.title}的对话`}
           hidden={!expanded}
         >
+          {sessionState.status === "ready" &&
+            sessionState.entries.length > 20 && (
+              <li>
+                <label className="workspace-session-search">
+                  <Search size={13} />
+                  <input
+                    aria-label={`搜索${board.title}的对话`}
+                    placeholder="搜索对话"
+                    value={query}
+                    onChange={(e) => setQuery(e.target.value)}
+                  />
+                </label>
+              </li>
+            )}
           {sessionItems}
+          {hidden > 0 && (
+            <li>
+              <button
+                className="workspace-session-more"
+                onClick={() => updateView({ all: true })}
+              >
+                <ChevronDown size={14} />
+                展开更多 · 还有 {hidden} 个
+              </button>
+            </li>
+          )}
           {current && (
             <li>
               <button
@@ -236,7 +415,7 @@ function BoardGroup({
                 disabled={disabled}
                 onClick={onNewSession}
               >
-                <Plus size={14} className="ico" />
+                <Plus size={13} className="ico" />
                 新对话
               </button>
             </li>
@@ -248,7 +427,13 @@ function BoardGroup({
 }
 
 /** One segment per card (a long list becomes one proportional bar); sealed segments are filled. */
-function Segments({ sealed, total }: { sealed: number; total: number }): ReactElement {
+function Segments({
+  sealed,
+  total,
+}: {
+  sealed: number;
+  total: number;
+}): ReactElement {
   if (total > 12)
     return (
       <span className="workspace-segs long" aria-hidden="true">
@@ -269,7 +454,8 @@ function Segments({ sealed, total }: { sealed: number; total: number }): ReactEl
 export function relativeDay(iso: string, today = new Date()): string {
   const d = new Date(iso);
   if (Number.isNaN(d.getTime())) return "";
-  const day = (x: Date) => new Date(x.getFullYear(), x.getMonth(), x.getDate()).getTime();
+  const day = (x: Date) =>
+    new Date(x.getFullYear(), x.getMonth(), x.getDate()).getTime();
   const diff = Math.round((day(today) - day(d)) / 86_400_000);
   if (diff === 0) return "今天";
   if (diff === 1) return "昨天";
@@ -345,6 +531,17 @@ export function WorkspaceSidebar({
     }
     return () => onResizingChange(false);
   }, [collapsed, onResizingChange]);
+  useEffect(() => {
+    if (!boards.length) return;
+    try {
+      const saved = JSON.parse(localStorage.getItem(SESSION_VIEW_KEY) ?? "{}");
+      for (const id of Object.keys(saved))
+        if (!boards.some((b) => b.id === id)) delete saved[id];
+      localStorage.setItem(SESSION_VIEW_KEY, JSON.stringify(saved));
+    } catch {
+      /* Storage can be unavailable. */
+    }
+  }, [boards]);
   const search = query.trim().toLocaleLowerCase();
   const visibleBoards = collapsed
     ? boards
@@ -368,17 +565,11 @@ export function WorkspaceSidebar({
           id: b.id,
           x: Math.max(
             8,
-            Math.min(
-              event.clientX || box.left,
-              window.innerWidth - 184,
-            ),
+            Math.min(event.clientX || box.left, window.innerWidth - 184),
           ),
           y: Math.max(
             8,
-            Math.min(
-              event.clientY || box.bottom,
-              window.innerHeight - 56,
-            ),
+            Math.min(event.clientY || box.bottom, window.innerHeight - 56),
           ),
           trigger: event.currentTarget,
         });
@@ -388,8 +579,16 @@ export function WorkspaceSidebar({
     />
   );
   const groups = [
-    { key: "active", label: "进行中", items: visibleBoards.filter((b) => !b.done) },
-    { key: "done", label: "已完成", items: visibleBoards.filter((b) => b.done) },
+    {
+      key: "active",
+      label: "进行中",
+      items: visibleBoards.filter((b) => !b.done),
+    },
+    {
+      key: "done",
+      label: "已完成",
+      items: visibleBoards.filter((b) => b.done),
+    },
   ];
 
   return (
@@ -420,12 +619,20 @@ export function WorkspaceSidebar({
           aria-controls="workspace-navigation"
           onClick={onToggle}
         >
-          {collapsed ? <PanelLeftOpen size={18} /> : <PanelLeftClose size={18} />}
+          {collapsed ? (
+            <PanelLeftOpen size={18} />
+          ) : (
+            <PanelLeftClose size={18} />
+          )}
         </button>
       </header>
       <div className="workspace-actions">
         {collapsed ? (
-          <button className="workspace-icon" {...tip("搜索画布与卡片", `${MOD}K`)} onClick={onSearch}>
+          <button
+            className="workspace-icon"
+            {...tip("搜索画布与卡片", `${MOD}K`)}
+            onClick={onSearch}
+          >
             <Search size={15} strokeWidth={2} />
           </button>
         ) : (
@@ -460,15 +667,44 @@ export function WorkspaceSidebar({
         id="workspace-navigation"
         className="workspace-navigation"
         aria-label="知识画布"
+        onKeyDown={(e) => {
+          if (
+            e.target instanceof HTMLInputElement ||
+            !["ArrowUp", "ArrowDown"].includes(e.key)
+          )
+            return;
+          const items = Array.from(
+            e.currentTarget.querySelectorAll<HTMLButtonElement>(
+              ".workspace-board, .workspace-session, .workspace-session-more, .workspace-empty button",
+            ),
+          ).filter((el) => !el.disabled && !el.closest("[hidden]") && el.getClientRects().length > 0);
+          const index = items.indexOf(e.target as HTMLButtonElement);
+          if (index < 0) return;
+          e.preventDefault();
+          e.stopPropagation();
+          items[
+            Math.max(
+              0,
+              Math.min(
+                items.length - 1,
+                index + (e.key === "ArrowDown" ? 1 : -1),
+              ),
+            )
+          ]?.focus();
+        }}
         aria-busy={switchingId !== null}
       >
-        <div className="workspace-board-list">
+        <div className="workspace-board-list" role="tree" aria-label="知识画布">
           {!boards.length && !collapsed ? (
             <p className="workspace-start">提一个问题，开始第一张画布</p>
           ) : (
             groups.map((g) =>
               g.items.length ? (
-                <section key={g.key} className="workspace-group" aria-label={g.label}>
+                <section
+                  key={g.key}
+                  className="workspace-group"
+                  aria-label={g.label}
+                >
                   {!collapsed && (
                     <h2 className="workspace-section">
                       {g.label} <span>{g.items.length}</span>
diff --git a/src/model/progress.ts b/src/model/progress.ts
index c212881..0bcdc36 100644
--- a/src/model/progress.ts
+++ b/src/model/progress.ts
@@ -12,5 +12,5 @@ export function boardProgress(board: Pick<Board, "nodes" | "wrap">): BoardProgre
   return { sealed, total, done: Boolean(board.wrap?.done) || (total > 0 && sealed === total) };
 }
 
-/** Save-time stamp; also the backfill for boards saved before progress existed. */
-export const withProgress = <B extends Board>(board: B): B => ({ ...board, progress: boardProgress(board) });
+/** Save-time metadata. listSessions currently includes every note, including saved annotations. */
+export const withProgress = <B extends Board>(board: B): B => ({ ...board, progress: boardProgress(board), sessionCount: board.notes.length });
diff --git a/src/model/sessions.ts b/src/model/sessions.ts
index 7a5b13b..5fe9af6 100644
--- a/src/model/sessions.ts
+++ b/src/model/sessions.ts
@@ -109,3 +109,27 @@ export function sessionClock(iso: string, now = new Date()): string {
     return `${d.getMonth() + 1}月${d.getDate()}日`;
   return `${d.getFullYear()}年${d.getMonth() + 1}月${d.getDate()}日`;
 }
+
+/** Keep the latest six and the active conversation in activity order. */
+export function visibleSessions(
+  entries: SessionEntry[],
+  activeId: string | undefined,
+  expandedAll: boolean,
+): { rows: SessionEntry[]; hidden: number } {
+  const sorted = [...entries].sort((a, b) => b.time.localeCompare(a.time));
+  const rows =
+    expandedAll || sorted.length <= 8
+      ? sorted
+      : sorted.filter((entry, i) => i < 6 || entry.id === activeId);
+  return { rows, hidden: entries.length - rows.length };
+}
+
+export function filterSessions(
+  entries: SessionEntry[],
+  query: string,
+): SessionEntry[] {
+  const q = query.trim().toLocaleLowerCase();
+  return entries.filter((entry) =>
+    `${entry.title} ${entry.anchorTitle}`.toLocaleLowerCase().includes(q),
+  );
+}
diff --git a/src/shared/types.ts b/src/shared/types.ts
index bb8809f..042693d 100644
--- a/src/shared/types.ts
+++ b/src/shared/types.ts
@@ -245,6 +245,7 @@ export interface Board {
   wrap?: { text: string; lit: string[]; missing?: string; done: boolean };
   /** Stamped on save for the sidebar list (model/progress.ts); older boards are backfilled on list. */
   progress?: BoardProgress;
+  sessionCount?: number;
 }
 export type ProbeVerdict = "correct" | "partial" | "wrong" | "unsure";
 /** One concept point of the probe's internal chain (shallow → deep). Never shown as a level. */
@@ -321,6 +322,8 @@ export interface BoardPlan {
   outOfScope: string[];
 }
 export interface BoardSummary {
+  /** Unknown on legacy saves until loaded or saved. */
+  sessionCount?: number;
   id: string;
   title: string;
   kind: Board["kind"];
diff --git a/src/shared/validation.ts b/src/shared/validation.ts
index 7d58d76..72d8b55 100644
--- a/src/shared/validation.ts
+++ b/src/shared/validation.ts
@@ -475,6 +475,7 @@ export const boardSchema = z
     createdAt: timestampSchema,
     updatedAt: timestampSchema,
     archivedAt: timestampSchema.optional(),
+    sessionCount: z.number().int().min(0).optional(),
     progress: z
       .object({ sealed: z.number().int().min(0), total: z.number().int().min(0), done: z.boolean() })
       .strict()
diff --git a/src/styles.css b/src/styles.css
index b8a626f..e4c45ed 100644
--- a/src/styles.css
+++ b/src/styles.css
@@ -4738,6 +4738,8 @@ kbd,
   --sb-ink: #2a2622;
   --sb-ink2: #6d665d;
   --sb-ink3: #9a9288;
+  --sb-ink3t: #70695f;
+  --sb-accchip: rgba(200, 68, 47, 0.12);
   --sb-accent: #c8442f;
   --sb-accent-bg: #f6e3dc;
   padding: var(--sidebar-content-top) 10px 10px;
@@ -4754,6 +4756,8 @@ kbd,
   --sb-ink: #ece6dc;
   --sb-ink2: #a8a097;
   --sb-ink3: #7b746b;
+  --sb-ink3t: #948d83;
+  --sb-accchip: rgba(224, 100, 77, 0.18);
   --sb-accent: #e0644d;
   --sb-accent-bg: #3a2621;
 }
@@ -4802,7 +4806,7 @@ kbd,
   border: 1px solid var(--sb-line);
   border-radius: 10px;
   box-shadow: none;
-  color: var(--sb-ink3);
+  color: var(--sb-ink3t);
 }
 .workspace-search:focus-within {
   border-color: var(--sb-accent);
@@ -4833,7 +4837,7 @@ h2.workspace-section {
 }
 h2.workspace-section span {
   font-weight: 400;
-  color: var(--sb-ink3);
+  color: var(--sb-ink3t);
 }
 .workspace-board-list ul {
   gap: 2px;
@@ -4884,7 +4888,7 @@ h2.workspace-section span {
   align-items: center;
   gap: 8px;
   font: 400 11.5px var(--kai);
-  color: var(--sb-ink3);
+  color: var(--sb-ink3t);
 }
 .workspace-date {
   margin-left: auto;
@@ -4919,28 +4923,259 @@ h2.workspace-section span {
 .workspace-done span {
   font-weight: 700;
 }
-/* Disclosure only on hover (or when open / current). */
+/* Session disclosure stays inside the board row. */
 .workspace-board-row {
   position: relative;
   align-items: flex-start;
+  border-radius: 10px;
+}
+.workspace-board-row:hover {
+  background: var(--sb-hover);
+}
+.workspace-board-row.is-current {
+  background: var(--sb-accent-bg);
+}
+.workspace-board-row.is-current::before {
+  content: "";
+  position: absolute;
+  left: 0;
+  top: 10px;
+  bottom: 10px;
+  width: 3px;
+  border-radius: 2px;
+  background: var(--sb-accent);
 }
 .workspace-board-row .workspace-board {
-  padding-left: 10px;
+  padding-left: 2px;
+  background: transparent;
+}
+.workspace-board-row .workspace-board::before {
+  display: none;
+}
+.workspace-board-row.has-sessions .workspace-board-title {
+  padding-right: 34px;
 }
 .workspace-disclosure {
+  position: static;
+  width: 24px;
+  height: 24px;
+  margin: 7px 0 0 2px;
+  border-radius: 8px;
+  color: var(--sb-ink3);
+}
+.workspace-disclosure.is-empty {
+  opacity: 0.45;
+}
+.workspace-session-count {
   position: absolute;
-  z-index: 1;
-  left: -8px;
-  top: 8px;
-  width: 16px;
-  height: 20px;
+  right: 8px;
+  top: 7px;
+  display: flex;
+  align-items: center;
+  gap: 3px;
+  min-width: 24px;
+  min-height: 24px;
+  padding: 0 7px 0 6px;
+  border-radius: 999px;
+  color: var(--sb-ink3t);
+  font-size: 11.5px;
+}
+.workspace-session-count svg {
+  color: var(--sb-ink3);
+}
+.workspace-session-count.is-open {
+  background: var(--sb-accchip);
+  color: var(--sb-accent);
+  font-weight: 700;
+}
+.workspace-session-count.is-open svg {
+  color: inherit;
+}
+.workspace-board-list .workspace-sessions {
+  margin: 0 0 6px 15px;
+  padding: 2px 0 0;
+  border-left: 1px solid var(--sb-line);
+  height: auto;
+  opacity: 1;
+  interpolate-size: allow-keywords;
+  transition:
+    height 150ms ease,
+    opacity 150ms ease,
+    display 150ms allow-discrete;
+}
+.workspace-sessions[hidden] {
+  height: 0;
   opacity: 0;
-  transition: opacity 120ms var(--ease-out);
+  overflow: clip;
+}
+@starting-style {
+  .workspace-sessions:not([hidden]) {
+    height: 0;
+    opacity: 0;
+    overflow: clip;
+  }
+}
+.workspace-sessions > li {
+  min-width: 0;
+}
+.workspace-session {
+  position: relative;
+  flex-direction: column;
+  justify-content: center;
+  align-items: stretch;
+  gap: 1px;
+  width: calc(100% - 11px);
+  height: 44px;
+  margin: 0 0 2px 11px;
+  padding: 0 8px 0 14px;
+  border-radius: 10px;
+  color: var(--sb-ink);
+}
+.workspace-session-title {
+  font: 400 13px/1.35 var(--kai);
+}
+.workspace-session .workspace-session-meta {
+  display: flex;
+  min-width: 0;
+  overflow: visible;
+  font: 400 11.5px/1.35 var(--kai);
+  color: var(--sb-ink3t);
+}
+.workspace-session-meta > span {
+  flex: 0 1 auto;
+  min-width: 0;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+.workspace-session-meta time {
+  flex: none;
+  margin-left: 4px;
+  white-space: nowrap;
+}
+.workspace-session[aria-current="page"] {
+  background: color-mix(in srgb, var(--sb-accent-bg) 60%, transparent);
+}
+.workspace-session[aria-current="page"] .workspace-session-title {
+  font-weight: 700;
 }
-.workspace-board-row:hover .workspace-disclosure,
-.workspace-disclosure:focus-visible,
-.workspace-disclosure[aria-expanded="true"] {
+.workspace-session-spinner {
+  width: 10px;
+  height: 10px;
+  border: 1.5px solid var(--sb-accchip);
+  border-top-color: var(--sb-accent);
+  border-radius: 50%;
+  position: absolute;
+  left: 2px;
+  top: calc(50% - 5px);
+  color: var(--sb-accent);
+}
+.workspace-session[aria-busy="true"] {
   opacity: 1;
+  pointer-events: none;
+}
+.workspace-session[aria-busy="true"] > span {
+  opacity: 0.85;
+}
+.workspace-session-more,
+.workspace-new-session {
+  display: flex;
+  align-items: center;
+  flex-direction: row;
+  justify-content: flex-start;
+  gap: 6px;
+  height: 32px;
+  width: calc(100% - 11px);
+  margin: 0 0 2px 11px;
+  padding: 0 8px 0 14px;
+  border-radius: 10px;
+  color: var(--sb-ink2);
+  font: 400 12.5px var(--kai);
+}
+.workspace-session-more:hover {
+  background: var(--sb-hover);
+}
+.workspace-new-session {
+  margin-top: 4px;
+  border: 1.25px dashed var(--sb-line);
+}
+.workspace-sessions .workspace-empty {
+  margin: 2px 0 0 11px;
+  padding: 6px 14px;
+  color: var(--sb-ink3t);
+  font: 400 12px/1.5 var(--kai);
+}
+.workspace-sessions .workspace-empty[role="alert"],
+.workspace-session-error {
+  color: var(--sb-ink2);
+}
+.workspace-empty button {
+  color: var(--sb-accent);
+  font-weight: 700;
+}
+.workspace-session-search {
+  display: flex;
+  align-items: center;
+  gap: 6px;
+  height: 30px;
+  margin: 2px 0 4px 11px;
+  padding: 0 8px;
+  background: var(--sb-card);
+  border: 1px solid var(--sb-line);
+  border-radius: 8px;
+  color: var(--sb-ink3);
+}
+.workspace-session-search input {
+  min-width: 0;
+  width: 100%;
+  border: 0;
+  outline: 0;
+  background: transparent;
+  color: var(--sb-ink);
+  font: 400 12.5px var(--kai);
+}
+.workspace-session-search input::placeholder {
+  color: var(--sb-ink3t);
+}
+.workspace-session-skeleton {
+  height: 44px;
+  margin-left: 11px;
+  padding: 0 14px;
+  display: flex;
+  flex-direction: column;
+  justify-content: center;
+  gap: 7px;
+}
+.workspace-session-skeleton i {
+  width: 68%;
+  height: 8px;
+  border-radius: 4px;
+  background: var(--sb-hover);
+  animation: workspace-pulse 1.4s ease-in-out infinite;
+}
+.workspace-session-skeleton i + i {
+  width: 44%;
+}
+@keyframes workspace-pulse {
+  50% {
+    opacity: 0.5;
+  }
+}
+.workspace-sidebar button:focus-visible,
+.workspace-session-search:focus-within {
+  outline: 2px solid var(--sb-accent);
+  outline-offset: -2px;
+}
+@media (prefers-reduced-motion: reduce) {
+  .workspace-sessions,
+  .workspace-session-skeleton i,
+  .workspace-session-spinner {
+    animation: none;
+    transition: none;
+  }
+  .workspace-disclosure svg {
+    transition: none;
+  }
 }
 .workspace-start {
   margin: 12px 0;
@@ -4985,7 +5220,14 @@ h2.workspace-section span {
   justify-items: center;
   padding-top: 6px;
 }
-.sidebar-collapsed .workspace-board {
+.sidebar-collapsed .workspace-board-row {
+  background: transparent;
+}
+.sidebar-collapsed .workspace-board-row::before {
+  display: none;
+}
+.sidebar-collapsed .workspace-board-row .workspace-board {
+  flex: none;
   align-items: center;
   width: 36px;
   height: 36px;
@@ -5015,10 +5257,18 @@ h2.workspace-section span {
   right: 0;
   bottom: 0;
   height: 3px;
-  background: linear-gradient(90deg, var(--sb-ink2) var(--p), var(--sb-line) var(--p));
+  background: linear-gradient(
+    90deg,
+    var(--sb-ink2) var(--p),
+    var(--sb-line) var(--p)
+  );
 }
 .sidebar-collapsed .workspace-board[aria-current="page"] .workspace-rail-bar {
-  background: linear-gradient(90deg, var(--sb-accent) var(--p), var(--sb-line) var(--p));
+  background: linear-gradient(
+    90deg,
+    var(--sb-accent) var(--p),
+    var(--sb-line) var(--p)
+  );
 }
 .sidebar-collapsed .workspace-board-list ul {
   gap: 8px;
diff --git a/tests/board-store.test.ts b/tests/board-store.test.ts
index fa397e7..584258a 100644
--- a/tests/board-store.test.ts
+++ b/tests/board-store.test.ts
@@ -12,7 +12,7 @@ import { join } from "node:path";
 import { boardProgress, withProgress } from "../src/model/progress";
 import { tmpdir } from "node:os";
 import { BoardStore } from "../electron/board-store";
-import { createEmptyBoard, createWalkthroughBoard } from "../src/model/boards";
+import { createEmptyBoard, createWalkthroughBoard, newNote } from "../src/model/boards";
 import { LIMITS } from "../src/shared/validation";
 
 let directory: string;
@@ -42,6 +42,7 @@ describe("atomic private board storage", () => {
       {
         id: board.id,
         title: board.title,
+        sessionCount: board.notes.length,
         kind: board.kind,
         updatedAt: board.updatedAt,
         ...boardProgress(board),
@@ -169,6 +170,21 @@ describe("atomic private board storage", () => {
       code: "TOO_LARGE",
     });
   });
+  it("recomputes session counts on save and preserves unknown legacy counts", async () => {
+    const board = createEmptyBoard("会话数量");
+    board.notes.push(newNote(board, { x: 0, y: 0 }));
+    board.sessionCount = 99;
+    await store.save(board);
+    expect((await store.load(board.id))?.sessionCount).toBe(1);
+    expect((await store.list())[0].sessionCount).toBe(1);
+    board.notes = [];
+    await store.save(board);
+    expect((await store.list())[0].sessionCount).toBe(0);
+    const path = join(directory, "boards", `${board.id}.json`);
+    const { sessionCount, ...legacy } = JSON.parse(await readFile(path, "utf8"));
+    await writeFile(path, JSON.stringify(legacy));
+    expect((await store.list())[0].sessionCount).toBeUndefined();
+  });
   it("backfills sealed/total for boards saved before progress existed", async () => {
     const board = createEmptyBoard("旧画布");
     board.nodes.push({ ...board.nodes[0], id: "c1", parentId: board.nodes[0].id, status: "explained" });
@@ -178,6 +194,6 @@ describe("atomic private board storage", () => {
     expect(progress).toEqual({ sealed: 1, total: 1, done: true });
     await writeFile(path, JSON.stringify(legacy));
     const [summary] = await new BoardStore(join(directory, "boards")).list();
-    expect(summary).toMatchObject({ sealed: 1, total: 1, done: true });
+    expect(summary).toMatchObject({ sealed: 1, total: 1, done: true, sessionCount: board.notes.length });
   });
 });
diff --git a/tests/e2e/drawer.spec.ts b/tests/e2e/drawer.spec.ts
index 0bef37c..b3d3ae5 100644
--- a/tests/e2e/drawer.spec.ts
+++ b/tests/e2e/drawer.spec.ts
@@ -109,10 +109,10 @@ test("single clicks follow the selected card and keep canvas shortcuts usable",
   await page
     .locator('.workspace-board[aria-current="page"]')
     .locator("..")
-    .getByRole("button", { name: /^展开/ })
+    .locator(".workspace-disclosure")
     .click();
   await expect(
-    page.locator('.workspace-session[aria-current="true"]'),
+    page.locator('.workspace-session[aria-current="page"]'),
   ).toContainText("保什么");
   await page
     .locator(".react-flow__pane")
diff --git a/tests/e2e/electron.spec.ts b/tests/e2e/electron.spec.ts
index 1c75a18..5276dcb 100644
--- a/tests/e2e/electron.spec.ts
+++ b/tests/e2e/electron.spec.ts
@@ -111,7 +111,7 @@ test("macOS desktop bridge, edit flush on immediate close, and durable reopening
     // The reopened board lists and selects that conversation in the sidebar.
     const current = nextPage
       .getByRole("complementary", { name: "学习空间", exact: true })
-      .locator('.workspace-session[aria-current="true"]');
+      .locator('.workspace-session[aria-current="page"]');
     await expect(current).toContainText("Close immediately");
     await expect(current).toHaveAttribute("title", /自由批注/);
     await nextPage.screenshot({
diff --git a/tests/e2e/fake-atlas.ts b/tests/e2e/fake-atlas.ts
index b40aebf..4b8cbfe 100644
--- a/tests/e2e/fake-atlas.ts
+++ b/tests/e2e/fake-atlas.ts
@@ -285,13 +285,14 @@ export async function installFakeAtlas(
         onBeforeClose: () => () => {},
         listBoards: async () =>
           [...boards.values()].map(
-            ({ id, title, kind, updatedAt, archivedAt, progress, nodes, wrap }) => {
+            ({ id, title, kind, updatedAt, archivedAt, progress, nodes, wrap, notes }) => {
               // Mirrors model/progress.ts (stored on save, backfilled on list), as the real store does.
               const cards = nodes.filter((n: any) => n.parentId !== null);
               const sealed = cards.filter((n: any) => n.status === "explained").length;
               return {
                 id,
                 title,
+                sessionCount: (window as any).__atlasLegacyCounts ? undefined : notes.length,
                 kind,
                 updatedAt,
                 ...(archivedAt ? { archivedAt } : {}),
diff --git a/tests/e2e/sessions.spec.ts b/tests/e2e/sessions.spec.ts
index 16a642d..9513ce1 100644
--- a/tests/e2e/sessions.spec.ts
+++ b/tests/e2e/sessions.spec.ts
@@ -34,7 +34,7 @@ test("sidebar conversations stay ordered, persist and reopen on their cards", as
   await page
     .locator('.workspace-board[aria-current="page"]')
     .locator("..")
-    .getByRole("button", { name: /^展开/ })
+    .locator(".workspace-disclosure")
     .click();
   const drawer = page.locator(".drawer");
   await card(page, "c-how").click();
@@ -44,16 +44,16 @@ test("sidebar conversations stay ordered, persist and reopen on their cards", as
   await ask(page, "间隔期是多久？");
   await expect(entries(page)).toHaveCount(3);
   await expect(entries(page).nth(0)).toContainText("间隔期是多久？");
-  await expect(entries(page).nth(0)).toHaveAttribute("aria-current", "true");
+  await expect(entries(page).nth(0)).toHaveAttribute("aria-current", "page");
   await expect(entries(page).nth(1)).toContainText("赔付次数怎么算？");
   await expect(entries(page).nth(2)).toContainText("带我起步");
   await expect(drawer.getByRole("group", { name: "对话标签" })).toHaveCount(0);
   await page
-    .getByRole("button", { name: `收起${seed.title}的对话`, exact: true })
+    .locator(".workspace-board-row.is-current .workspace-disclosure")
     .click();
   await expect(entries(page)).toHaveCount(0);
   await page
-    .getByRole("button", { name: `展开${seed.title}的对话`, exact: true })
+    .locator(".workspace-board-row.is-current .workspace-disclosure")
     .click();
   await expect(entries(page)).toHaveCount(3);
   await expect
@@ -65,12 +65,7 @@ test("sidebar conversations stay ordered, persist and reopen on their cards", as
     )
     .toBe(3);
   await reloadApp(page);
-  await expect(entries(page)).toHaveCount(0);
-  await page
-    .locator('.workspace-board[aria-current="page"]')
-    .locator("..")
-    .getByRole("button", { name: /^展开/ })
-    .click();
+  await expect(entries(page)).not.toHaveCount(0);
   await entries(page).filter({ hasText: "赔付次数怎么算？" }).click();
   await expect(drawer.locator(".msg.user")).toHaveText("赔付次数怎么算？");
   await expect(card(page, "c-how")).toHaveClass(/selected/);
@@ -94,22 +89,27 @@ test("expanding another canvas lists its sessions and opens the selected convers
   await page
     .locator('.workspace-board[aria-current="page"]')
     .locator("..")
-    .getByRole("button", { name: /^展开/ })
+    .locator(".workspace-disclosure")
     .click();
   await page
-    .getByRole("button", { name: "展开另一个画布的对话", exact: true })
+    .getByRole("treeitem", { name: "另一个画布", exact: true })
+    .locator(".workspace-disclosure")
     .click();
   const target = entries(page).filter({ hasText: "另一个画布的会话" });
   await expect(target).toBeVisible();
   await expect(
-    page.locator('.workspace-board[aria-current="page"] .workspace-board-title'),
+    page.locator(
+      '.workspace-board[aria-current="page"] .workspace-board-title',
+    ),
   ).toHaveText(first.title);
   await target.click();
   await expect(
-    page.locator('.workspace-board[aria-current="page"] .workspace-board-title'),
+    page.locator(
+      '.workspace-board[aria-current="page"] .workspace-board-title',
+    ),
   ).toHaveText(second.title);
   await expect(page.getByLabel("批注标题")).toHaveValue("另一个画布的会话");
-  await expect(target).toHaveAttribute("aria-current", "true");
+  await expect(target).toHaveAttribute("aria-current", "page");
 });
 
 test("web preview conversations persist and the sidebar can create a new conversation", async ({
@@ -127,7 +127,7 @@ test("web preview conversations persist and the sidebar can create a new convers
   await page
     .locator('.workspace-board[aria-current="page"]')
     .locator("..")
-    .getByRole("button", { name: /^展开/ })
+    .locator(".workspace-disclosure")
     .click();
   await page.getByRole("button", { name: "新对话", exact: true }).click();
   await page.getByLabel("批注标题").fill("犹豫期的问题");
@@ -142,15 +142,10 @@ test("web preview conversations persist and the sidebar can create a new convers
     )
     .toBe(2);
   await reloadApp(page);
-  await expect(entries(page)).toHaveCount(0);
-  await page
-    .locator('.workspace-board[aria-current="page"]')
-    .locator("..")
-    .getByRole("button", { name: /^展开/ })
-    .click();
+  await expect(entries(page)).not.toHaveCount(0);
   await entries(page).filter({ hasText: "犹豫期的问题" }).click();
   await expect(page.getByLabel("批注标题")).toHaveValue("犹豫期的问题");
   await expect(
     entries(page).filter({ hasText: "犹豫期的问题" }),
-  ).toHaveAttribute("aria-current", "true");
+  ).toHaveAttribute("aria-current", "page");
 });
diff --git a/tests/e2e/sidebar-sessions.spec.ts b/tests/e2e/sidebar-sessions.spec.ts
new file mode 100644
index 0000000..777efe1
--- /dev/null
+++ b/tests/e2e/sidebar-sessions.spec.ts
@@ -0,0 +1,304 @@
+import { test, expect, type Page } from "@playwright/test";
+import { mkdirSync } from "node:fs";
+import { installFakeAtlas } from "./fake-atlas";
+import { insuranceBoard } from "./fixtures";
+import { gotoApp, reloadApp } from "./ready";
+
+const rows = (page: Page) =>
+  page.locator(
+    '.workspace-sessions:visible .workspace-session[role="treeitem"]',
+  );
+const group = (page: Page, id: string) =>
+  page.locator(
+    `li[role="treeitem"]:has(> .workspace-board-row > .workspace-disclosure[aria-controls="sessions-${id}"])`,
+  );
+const toggle = (page: Page, id: string) =>
+  group(page, id).locator(".workspace-disclosure");
+
+function canvas(id: string, count: number, offset = 0) {
+  const board = insuranceBoard(true);
+  board.id = id;
+  board.title = `画布 ${id}`;
+  board.updatedAt = new Date(Date.now() - offset * 86400000).toISOString();
+  const template = board.notes[0];
+  board.notes = Array.from({ length: count }, (_, i) => ({
+    ...structuredClone(template),
+    id: `${id}-session-${i}`,
+    title: `对话 ${i + 1}`,
+    attachedTo: {
+      kind: "node" as const,
+      id: i === count - 1 ? "c-how" : board.nodes[0].id,
+    },
+    messages: template.messages.map((m) => ({
+      ...m,
+      createdAt: new Date(Date.now() - i * 86400000).toISOString(),
+    })),
+  }));
+  return board;
+}
+
+async function holdLoads(page: Page, id: string, fail = false) {
+  await page.evaluate(
+    ({ id, fail }) => {
+      const w = window as any;
+      const original = w.atlas.loadBoard;
+      w.__sessionLoadCalls = 0;
+      w.atlas.loadBoard = async (boardId: string) => {
+        if (boardId === id) {
+          w.__sessionLoadCalls++;
+          if (fail) throw new Error("fixture read failure");
+          await new Promise<void>((resolve) => {
+            w.__releaseSessionLoad = resolve;
+          });
+        }
+        return original(boardId);
+      };
+      w.__restoreSessionLoads = () => {
+        w.atlas.loadBoard = original;
+      };
+    },
+    { id, fail },
+  );
+}
+
+async function releaseLoads(page: Page) {
+  await page.evaluate(() => {
+    (window as any).__restoreSessionLoads();
+    (window as any).__releaseSessionLoad?.();
+  });
+}
+
+test("disclosures and counts stay visible; canvas selection preserves persisted expansion", async ({
+  page,
+}) => {
+  const a = canvas("a", 2),
+    b = canvas("b", 3, 1);
+  await installFakeAtlas(page, true, "web", [a, b]);
+  await gotoApp(page);
+  await expect(rows(page)).toHaveCount(0);
+  const arrow = toggle(page, a.id);
+  await expect(arrow).toHaveCSS("opacity", "1");
+  const box = (await arrow.boundingBox())!;
+  expect(box.width).toBeGreaterThanOrEqual(24);
+  expect(box.height).toBeGreaterThanOrEqual(24);
+  await group(page, b.id).locator(".workspace-session-count").click();
+  await expect(
+    group(page, b.id).locator('.workspace-session[role="treeitem"]'),
+  ).toHaveCount(3);
+  await expect(group(page, a.id)).toHaveAttribute("aria-current", "true");
+  await page.getByRole("button", { name: a.title, exact: true }).click();
+  await expect(arrow).toHaveAttribute("aria-expanded", "false");
+  await toggle(page, b.id).click();
+  await page.getByRole("button", { name: b.title, exact: true }).click();
+  await expect(toggle(page, b.id)).toHaveAttribute("aria-expanded", "false");
+  await arrow.click();
+  await reloadApp(page);
+  await expect(arrow).toHaveAttribute("aria-expanded", "true");
+  await expect(toggle(page, b.id)).toHaveAttribute("aria-expanded", "false");
+});
+
+test("twelve sessions retain the older current conversation; show all persists and time survives narrow width", async ({
+  page,
+}) => {
+  const board = canvas("twelve", 12);
+  await installFakeAtlas(page, true, "web", [board]);
+  await gotoApp(page);
+  await toggle(page, board.id).click();
+  await expect(rows(page)).toHaveCount(6);
+  await expect(
+    page.getByRole("button", { name: "展开更多 · 还有 6 个" }),
+  ).toBeVisible();
+  await page.locator('.react-flow__node[data-id="c-how"]').click();
+  await expect(rows(page)).toHaveCount(7);
+  await expect(rows(page).last()).toHaveAttribute("aria-current", "page");
+  await expect(
+    page.getByRole("button", { name: "展开更多 · 还有 5 个" }),
+  ).toBeVisible();
+  await toggle(page, board.id).click();
+  await expect(
+    group(page, board.id).locator(".workspace-session-count"),
+  ).toHaveClass(/is-open/);
+  await toggle(page, board.id).click();
+  await page.getByRole("button", { name: "展开更多 · 还有 5 个" }).click();
+  await expect(rows(page)).toHaveCount(12);
+  await reloadApp(page);
+  await expect(rows(page)).toHaveCount(12);
+  const handle = page.getByRole("separator", { name: "调整左侧栏宽度" });
+  await handle.focus();
+  await handle.press("Home");
+  await expect(rows(page).first().locator("time")).toBeVisible();
+  await expect(rows(page).first()).toHaveCSS("height", "44px");
+});
+
+test("search filters title and anchor above twenty sessions without nested scrolling", async ({
+  page,
+}) => {
+  const board = canvas("search", 21);
+  board.notes[20].title = "犹豫期的问题";
+  await installFakeAtlas(page, true, "web", [board]);
+  await gotoApp(page);
+  await toggle(page, board.id).click();
+  const input = page.getByPlaceholder("搜索对话");
+  await input.fill("犹豫期");
+  await expect(rows(page)).toHaveCount(1);
+  await expect(rows(page)).toContainText("犹豫期的问题");
+  await input.fill("不存在的问题");
+  await expect(page.getByText("没有匹配的对话", { exact: true })).toBeVisible();
+  await input.fill("起点问题");
+  await expect(rows(page)).toHaveCount(20);
+  await expect(
+    group(page, board.id).locator(".workspace-sessions"),
+  ).not.toHaveCSS("overflow-y", "auto");
+});
+
+test("keyboard navigates visible rows and expands without selecting another canvas", async ({
+  page,
+}) => {
+  const a = canvas("keyboard", 2),
+    b = canvas("other", 1, 1);
+  await installFakeAtlas(page, true, "web", [a, b]);
+  await gotoApp(page);
+  const boardButton = page.getByRole("button", { name: a.title, exact: true });
+  await boardButton.focus();
+  await boardButton.press("ArrowRight");
+  await expect(toggle(page, a.id)).toHaveAttribute("aria-expanded", "true");
+  await boardButton.press("ArrowDown");
+  await expect(rows(page).first()).toBeFocused();
+  await rows(page).first().press("Enter");
+  await expect(rows(page).first()).toHaveAttribute("aria-current", "page");
+  await toggle(page, b.id).focus();
+  await toggle(page, b.id).press("Space");
+  await expect(toggle(page, b.id)).toHaveAttribute("aria-expanded", "true");
+  await expect(group(page, a.id)).toHaveAttribute("aria-current", "true");
+  await boardButton.focus();
+  await boardButton.press("ArrowLeft");
+  await expect(toggle(page, a.id)).toHaveAttribute("aria-expanded", "false");
+});
+
+test("lazy loading, cached reopen, errors, retries and cross-canvas switching are explicit", async ({
+  page,
+}) => {
+  const a = canvas("current", 0),
+    b = canvas("remote", 2, 1);
+  await installFakeAtlas(page, true, "web", [a, b]);
+  await gotoApp(page);
+  await toggle(page, a.id).click();
+  await expect(group(page, a.id)).toContainText("还没有对话");
+  await expect(
+    group(page, a.id).getByRole("button", { name: "新对话" }),
+  ).toBeVisible();
+  await holdLoads(page, b.id);
+  await toggle(page, b.id).click();
+  await expect(group(page, b.id)).toContainText("正在读取对话…");
+  await expect(
+    group(page, b.id).locator(".workspace-session-skeleton"),
+  ).toHaveCount(2);
+  await releaseLoads(page);
+  await expect(rows(page)).toHaveCount(2);
+  await holdLoads(page, b.id, true);
+  await toggle(page, b.id).click();
+  await toggle(page, b.id).click();
+  await expect(rows(page)).toHaveCount(2);
+  expect(await page.evaluate(() => (window as any).__sessionLoadCalls)).toBe(0);
+  await rows(page).first().click();
+  await expect(group(page, b.id)).toContainText("无法打开 ·");
+  await releaseLoads(page);
+  await holdLoads(page, b.id);
+  await group(page, b.id).getByRole("button", { name: "重试" }).click();
+  await expect(rows(page).first()).toHaveAttribute("aria-busy", "true");
+  await expect(
+    rows(page).first().locator(".workspace-session-spinner"),
+  ).toBeVisible();
+  await expect(rows(page).first()).toBeDisabled();
+  await releaseLoads(page);
+  await expect(rows(page).first()).toHaveAttribute("aria-current", "page");
+  await expect(group(page, b.id)).toHaveAttribute("aria-current", "true");
+  await expect(page.locator(".drawer")).toBeVisible();
+});
+
+test("failed first read can retry; unknown legacy counts appear after loading", async ({
+  page,
+}) => {
+  const a = canvas("current", 0),
+    b = canvas("legacy", 1, 1);
+  await installFakeAtlas(page, true, "web", [a, b]);
+  await page.addInitScript(() => {
+    (window as any).__atlasLegacyCounts = true;
+  });
+  await gotoApp(page);
+  await expect(
+    group(page, b.id).locator(".workspace-session-count"),
+  ).toHaveCount(0);
+  await holdLoads(page, b.id, true);
+  await toggle(page, b.id).click();
+  await expect(group(page, b.id)).toContainText("无法读取对话");
+  await releaseLoads(page);
+  await group(page, b.id).getByRole("button", { name: "重试" }).click();
+  await expect(rows(page)).toHaveCount(1);
+  await expect(
+    group(page, b.id).locator(".workspace-session-count"),
+  ).toHaveText("1");
+});
+
+for (const scheme of ["light", "dark"] as const) {
+  test(`session design screenshots · ${scheme}`, async ({ page }) => {
+    const dir = process.env.SHOTS_DIR;
+    test.skip(!dir, "set SHOTS_DIR to capture the sidebar session states");
+    mkdirSync(dir!, { recursive: true });
+    await page.emulateMedia({ colorScheme: scheme });
+    const a = canvas("twelve", 12),
+      empty = canvas("empty", 0, 1),
+      loading = canvas("loading", 2, 2),
+      error = canvas("error", 1, 3);
+    await installFakeAtlas(page, true, "web", [a, empty, loading, error]);
+    await gotoApp(page);
+    const shot = async (name: string) => {
+      await page.evaluate(() => document.fonts.ready);
+      // Let the disclosure height/opacity transition settle.
+      await page.waitForTimeout(500);
+      await page.screenshot({ path: `${dir}/sessions-${scheme}-${name}.png` });
+    };
+    await shot("collapsed");
+    await toggle(page, a.id).click();
+    await shot("expanded");
+    await page.locator('.react-flow__node[data-id="c-how"]').click();
+    await shot("twelve-current");
+    await rows(page).nth(1).hover();
+    await rows(page).nth(1).focus();
+    await page.keyboard.press("ArrowDown");
+    await shot("hover-focus");
+    await toggle(page, a.id).click();
+    await shot("collapsed-current");
+    await toggle(page, empty.id).click();
+    await holdLoads(page, loading.id);
+    await toggle(page, loading.id).click();
+    await expect(group(page, loading.id)).toContainText("正在读取对话…");
+    await shot("empty-loading");
+    await releaseLoads(page);
+    await expect(
+      group(page, loading.id).locator('.workspace-session[role="treeitem"]'),
+    ).toHaveCount(2);
+    await holdLoads(page, error.id, true);
+    await toggle(page, error.id).click();
+    await expect(group(page, error.id)).toContainText("无法读取对话");
+    await shot("read-error");
+    await releaseLoads(page);
+    await holdLoads(page, loading.id);
+    await group(page, loading.id)
+      .locator('.workspace-session[role="treeitem"]')
+      .first()
+      .click();
+    await expect(
+      group(page, loading.id).locator('[aria-busy="true"]'),
+    ).toBeVisible();
+    await shot("switching");
+    await releaseLoads(page);
+    await expect(group(page, loading.id)).toHaveAttribute(
+      "aria-current",
+      "true",
+    );
+    await page.getByRole("button", { name: empty.title, exact: true }).click();
+    await expect(group(page, empty.id).getByRole("button", { name: "新对话" })).toBeVisible();
+    await shot("empty-current");
+  });
+}
diff --git a/tests/sessions.test.ts b/tests/sessions.test.ts
index d9848d6..66c8bdd 100644
--- a/tests/sessions.test.ts
+++ b/tests/sessions.test.ts
@@ -2,6 +2,8 @@ import { describe, expect, it } from "vitest";
 import { createWalkthroughBoard, newNote } from "../src/model/boards";
 import {
   latestNoteOn,
+  visibleSessions,
+  filterSessions,
   listSessions,
   sessionClock,
   stripOrder,
@@ -153,3 +155,33 @@ describe("drawer session strip", () => {
     ]);
   });
 });
+
+describe("sidebar session window", () => {
+  const entries = Array.from({ length: 12 }, (_, i) => ({
+    ...listSessions(board().b)[0],
+    id: `s-${i}`,
+    title: `Title ${i}`,
+    anchorTitle: i === 9 ? "特别锚点" : "卡片",
+    time: new Date(2026, 0, 12 - i).toISOString(),
+  }));
+  it("keeps six recent rows and an older active session, without duplicates", () => {
+    expect(visibleSessions(entries, "s-9", false)).toEqual({
+      rows: [...entries.slice(0, 6), entries[9]],
+      hidden: 5,
+    });
+    expect(visibleSessions(entries, "s-0", false).hidden).toBe(6);
+    expect(
+      visibleSessions(entries.slice(0, 8), undefined, false).rows,
+    ).toHaveLength(8);
+    expect(visibleSessions(entries, undefined, true).hidden).toBe(0);
+    expect(visibleSessions([], undefined, false)).toEqual({
+      rows: [],
+      hidden: 0,
+    });
+  });
+  it("filters titles and anchors without changing activity order", () => {
+    expect(filterSessions(entries, " 特别 ")).toEqual([entries[9]]);
+    expect(filterSessions(entries, "TITLE 11")).toEqual([entries[11]]);
+    expect(filterSessions(entries, "missing")).toEqual([]);
+  });
+});
diff --git a/tests/sidebar-sessions.test.ts b/tests/sidebar-sessions.test.ts
new file mode 100644
index 0000000..02fc633
--- /dev/null
+++ b/tests/sidebar-sessions.test.ts
@@ -0,0 +1,64 @@
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { createElement, type ComponentProps } from "react";
+import { renderToStaticMarkup } from "react-dom/server";
+import { WorkspaceSidebar } from "../src/components/WorkspaceSidebar";
+import { listSessions } from "../src/model/sessions";
+import { createWalkthroughBoard, newNote } from "../src/model/boards";
+
+vi.mock("../src/api", () => ({ api: { loadBoard: vi.fn() } }));
+afterEach(() => vi.unstubAllGlobals());
+
+function render(options: Partial<ComponentProps<typeof WorkspaceSidebar>> = {}) {
+  const props: ComponentProps<typeof WorkspaceSidebar> = {
+    boards: [{ id: "board", title: "画布", kind: "walkthrough", updatedAt: new Date().toISOString(), sessionCount: 12 }],
+    currentId: "board", collapsed: false, switchingId: null, width: 256,
+    onWidthChange() {}, onResizingChange() {}, onToggle() {}, onPick() {}, onArchive() {}, onNew() {}, onSearch() {}, onSettings() {},
+    sessions: [], onOpenSession: async () => {}, onNewSession() {}, ...options,
+  };
+  return renderToStaticMarkup(createElement(WorkspaceSidebar, props));
+}
+
+function saved(view: unknown) {
+  vi.stubGlobal("localStorage", { getItem: () => JSON.stringify(view) });
+}
+
+describe("sidebar session rendering", () => {
+  it("starts collapsed even when a conversation is open, with an accented count and accessible disclosure", () => {
+    const board = createWalkthroughBoard();
+    board.notes.push(newNote(board, { x: 0, y: 0 }));
+    const html = render({ sessions: listSessions(board), currentSessionId: board.notes[0].id });
+    expect(html).toContain('role="tree"');
+    expect(html).toContain('aria-label="展开对话（1）"');
+    expect(html).toContain('aria-controls="sessions-board"');
+    expect(html).toContain('workspace-session-count is-open');
+    expect(html).toContain('hidden=""');
+    expect(html).not.toContain('workspace-session-spinner');
+  });
+
+  it("respects saved expansion and pins the older active row with its two lines of metadata", () => {
+    saved({ board: { open: true, all: false } });
+    const board = createWalkthroughBoard();
+    board.notes = Array.from({ length: 12 }, (_, i) => {
+      const note = newNote(board, { x: 0, y: 0 });
+      note.title = `对话 ${i}`;
+      note.createdAt = new Date(2026, 0, 12 - i).toISOString();
+      return note;
+    });
+    const html = render({ sessions: listSessions(board), currentSessionId: board.notes[10].id });
+    expect(html).toContain('aria-label="收起对话（12）"');
+    expect(html).not.toContain('hidden=""');
+    expect(html.match(/class="workspace-session"/g)).toHaveLength(7);
+    expect(html).toContain('aria-current="page" aria-busy="false"');
+    expect(html).toContain('workspace-session-meta');
+    expect(html).toContain('自由批注');
+    expect(html).toContain('展开更多 · 还有 5 个');
+  });
+
+  it("hides unknown counts and omits disclosure and sessions in the collapsed rail", () => {
+    const board = { id: "other", title: "旧画布", kind: "walkthrough" as const, updatedAt: new Date().toISOString() };
+    expect(render({ boards: [board] })).not.toContain('class="workspace-session-count');
+    const rail = render({ boards: [board], collapsed: true });
+    expect(rail).not.toContain('workspace-disclosure');
+    expect(rail).not.toContain('workspace-sessions');
+  });
+});