diff --git a/README.md b/README.md
index 1ba755cd..fd80b9a5 100644
--- a/README.md
+++ b/README.md
@@ -37,7 +37,7 @@ The public demo resets every Monday at 1:00 AM (China Standard Time) and restore
 - Batch note merging.
 - Batch note moving, notebook drag sorting, and hierarchy editing.
 - Offline drafts and local sync queue for existing notes.
-- Single-user login with PBKDF2-SHA256 password hashing.
+- Multi-user instances with isolated personal workspaces, owner-managed accounts, and PBKDF2-SHA256 password hashing.
 - Chrome/Edge web clipper is complete and pending store publication.
 
 ## Deployment
@@ -71,6 +71,10 @@ Please refer to the [Cloudflare Manual Deployment Guide](docs/manual-deploy.md)
 The automated helper commands are recommended. The template uses `admin` / `admin123` for the initial login, and the password can be changed later in Personal Settings. If you create the Cloudflare resources manually, finish configuring `.env.local`—including the D1 ID, R2 bucket, and the 400-day session limit—before running `bun run deploy`. Existing installations that use `EDGE_EVER_AUTH_PASSWORD_HASH` remain supported. Use that command only for first installation and emergency recovery; Workers Builds handles routine updates.
 
 
+## Multi-user Instances
+
+The instance owner can create, disable, and reset member accounts in **Profile** -> **User accounts**. Public registration is disabled. Every member gets an isolated personal workspace, including notebooks, notes, attachments, Trash, imports/exports, and MCP tokens. Existing single-user installations are migrated automatically: all existing data remains in the original owner's default workspace. Cloudflare free-tier quotas are shared by the whole instance rather than allocated per user.
+
 ## PWA Installation
 
 EdgeEver can be installed as a PWA on desktop or mobile home screens. On desktop, open the site in Chrome or Edge and use the install icon in the address bar. On Android, open it in Chrome, use the three-dot menu, and choose **Add to Home screen** or **Install**. Avoid installing from embedded browsers such as WeChat.
diff --git a/README.zh-CN.md b/README.zh-CN.md
index b25d54ea..f3e1670d 100644
--- a/README.zh-CN.md
+++ b/README.zh-CN.md
@@ -39,7 +39,7 @@ EdgeEver 想填补这个空白：保留熟悉的笔记体验，同时提供开
 - 多选合并笔记。
 - 多选移动笔记，笔记本支持拖拽排序和调整层级。
 - 已有笔记支持离线编辑草稿和本地同步队列。
-- 单用户登录，密码使用 PBKDF2-SHA256 hash。
+- 支持单实例多账号，每个账号拥有隔离的个人笔记空间；管理员可创建、停用和重置成员账号，密码使用 PBKDF2-SHA256 hash。
 - Chrome/Edge 网页裁剪插件已开发完成，待上架。
 
 ## 部署
@@ -71,6 +71,10 @@ Agent 应优先按 [AI Agent Cloudflare Deployment](docs/agent-deploy-cloudflare
 推荐优先使用自动化辅助命令。如果选择完全手动创建 Cloudflare 资源，必须先在 `.env.local` 中完成 D1 ID、R2 bucket、密码 hash 和 400 天会话期限等配置，再执行 `bun run deploy`。该命令仅用于首次安装和紧急修复；日常更新由 Workers Builds 自动完成。
 
 
+## 多账号实例
+
+实例管理员可以在 **个人中心** -> **账号管理** 中创建、停用成员账号或重置密码，实例默认不开放公开注册。每个成员拥有完全隔离的个人空间，包括笔记本、笔记、附件、回收站、导入导出和 MCP Token。已有单用户实例升级时会自动把全部原数据归入原管理员的默认空间，不改变原有数据 ID。Cloudflare 免费额度由整个实例共同使用，不会按账号分别增加。
+
 ## PWA 安装说明
 
 PWA 可以把 EdgeEver 像普通应用一样安装到桌面或手机主屏幕，打开更方便，也能配合浏览器能力提供更接近原生 App 的使用体验。
diff --git a/apps/api/src/index.ts b/apps/api/src/index.ts
index d9e509f2..302d9d76 100644
--- a/apps/api/src/index.ts
+++ b/apps/api/src/index.ts
@@ -18,6 +18,8 @@ import {
   MoveMemosSchema,
   normalizeTags,
   TagRenameSchema,
+  UserCreateSchema,
+  UserUpdateSchema,
   NotebookCreateSchema,
   NotebookUpdateSchema,
   RestoreJsonMemosSchema,
@@ -40,6 +42,7 @@ import {
   type ResourceStorageSummary,
   type TagSummary,
   type TiptapDoc,
+  type InstanceUser,
 } from "@edgeever/shared";
 import { zValidator } from "@hono/zod-validator";
 import type { Context } from "hono";
@@ -68,6 +71,8 @@ type AuthContext = {
   username: string;
   displayName: string | null;
   scopes: string[];
+  workspaceId: string;
+  role: "owner" | "member";
   sessionId?: string;
   tokenId?: string;
 };
@@ -164,6 +169,12 @@ type UserRow = {
   is_disabled: number;
 };
 
+type InstanceUserRow = UserRow & {
+  last_login_at: string | null;
+  created_at: string;
+  role: "owner" | "member";
+};
+
 type SessionRow = {
   id: string;
   user_id: string;
@@ -181,6 +192,7 @@ type ApiTokenRow = {
   expires_at: string | null;
   is_revoked: number;
   created_at: string;
+  workspace_id: string;
 };
 
 type TagSummaryRow = {
@@ -229,6 +241,7 @@ type ResourceStatsRow = {
 type AppContext = Context<{ Bindings: Bindings; Variables: { auth: AuthContext } }>;
 
 const SESSION_COOKIE = "edgeever_session";
+const DEFAULT_WORKSPACE_ID = "ws_default";
 const DEFAULT_MEMO_LIST_LIMIT = 100;
 const MAX_MEMO_LIST_LIMIT = 200;
 const UNTITLED_MEMO_TITLE = "无标题笔记";
@@ -422,6 +435,7 @@ app.get("/api/v1/auth/session", async (c) => {
         id: "local",
         username: "owner",
         displayName: "Owner",
+        role: "owner",
       },
     });
   }
@@ -437,6 +451,7 @@ app.get("/api/v1/auth/session", async (c) => {
             id: auth.actorId,
             username: auth.username,
             displayName: auth.displayName,
+            role: auth.role,
           }
         : null,
   });
@@ -450,6 +465,7 @@ app.post("/api/v1/auth/login", zValidator("json", LoginSchema), async (c) => {
     return unauthorized(c, "Username or password is incorrect.");
   }
 
+  const workspace = await ensureUserWorkspace(c.env.DB, user.id, user.username);
   const session = await createSession(c, user);
   setSessionCookie(c, session.token, session.maxAge);
 
@@ -472,6 +488,7 @@ app.post("/api/v1/auth/login", zValidator("json", LoginSchema), async (c) => {
       id: user.id,
       username: user.username,
       displayName: user.display_name,
+      role: workspace.role,
     },
   });
 });
@@ -515,6 +532,109 @@ app.post("/api/v1/auth/change-password", zValidator("json", ChangePasswordSchema
   return c.json({ ok: true });
 });
 
+app.get("/api/v1/users", async (c) => {
+  const auth = await authenticateSession(c, true);
+  if (!auth) return unauthorized(c, "Authentication required.");
+  c.set("auth", auth);
+  const denied = requireOwner(c);
+  if (denied) return denied;
+
+  const rows = await c.env.DB.prepare(
+    `SELECT u.id, u.username, u.password_hash, u.display_name, u.is_disabled,
+            u.last_login_at, u.created_at, wm.role
+     FROM users u
+     INNER JOIN workspace_members wm ON wm.user_id = u.id
+     ORDER BY wm.role = 'owner' DESC, u.created_at ASC`
+  ).all<InstanceUserRow>();
+
+  return c.json({ users: rows.results.map(mapInstanceUser) });
+});
+
+app.post("/api/v1/users", zValidator("json", UserCreateSchema), async (c) => {
+  const auth = await authenticateSession(c, true);
+  if (!auth) return unauthorized(c, "Authentication required.");
+  c.set("auth", auth);
+  const denied = requireOwner(c);
+  if (denied) return denied;
+
+  const input = c.req.valid("json");
+  const existing = await c.env.DB.prepare(`SELECT id FROM users WHERE username = ?`).bind(input.username).first();
+  if (existing) return conflict(c, "username_exists", "Username already exists.");
+
+  const userId = createId("usr");
+  const workspaceId = createId("ws");
+  const now = isoNow();
+  const passwordHash = await hashPassword(input.password);
+  const notebooks = createDefaultNotebookRows(workspaceId, now);
+  const statements = [
+    c.env.DB.prepare(
+      `INSERT INTO users (id, username, password_hash, display_name, created_at, updated_at)
+       VALUES (?, ?, ?, ?, ?, ?)`
+    ).bind(userId, input.username, passwordHash, input.displayName ?? input.username, now, now),
+    c.env.DB.prepare(`INSERT INTO workspaces (id, name, is_personal, created_at, updated_at) VALUES (?, ?, 1, ?, ?)`)
+      .bind(workspaceId, `${input.displayName ?? input.username}'s workspace`, now, now),
+    c.env.DB.prepare(`INSERT INTO workspace_members (workspace_id, user_id, role, created_at) VALUES (?, ?, 'member', ?)`)
+      .bind(workspaceId, userId, now),
+    ...notebooks.map((notebook) => c.env.DB.prepare(
+      `INSERT INTO notebooks (id, workspace_id, parent_id, name, slug, icon, color, sort_order, created_at, updated_at)
+       VALUES (?, ?, NULL, ?, ?, 'notebook', ?, ?, ?, ?)`
+    ).bind(notebook.id, workspaceId, notebook.name, notebook.slug, notebook.color, notebook.sortOrder, now, now)),
+    auditStatement(c.env.DB, "user", c.get("auth").actorId, "user.create", "user", userId, { username: input.username }),
+  ];
+  await c.env.DB.batch(statements);
+
+  const user = await getInstanceUser(c.env.DB, userId);
+  return c.json({ user: user ? mapInstanceUser(user) : null }, 201);
+});
+
+app.patch("/api/v1/users/:id", zValidator("json", UserUpdateSchema), async (c) => {
+  const auth = await authenticateSession(c, true);
+  if (!auth) return unauthorized(c, "Authentication required.");
+  c.set("auth", auth);
+  const denied = requireOwner(c);
+  if (denied) return denied;
+
+  const userId = c.req.param("id");
+  const input = c.req.valid("json");
+  const current = await getInstanceUser(c.env.DB, userId);
+  if (!current) return notFound(c, "User not found");
+  if (current.role === "owner" && input.isDisabled === true) {
+    return badRequest(c, "The instance owner cannot be disabled.");
+  }
+
+  const updates: string[] = [];
+  const binds: unknown[] = [];
+  if (input.displayName !== undefined) {
+    updates.push("display_name = ?");
+    binds.push(input.displayName);
+  }
+  if (input.password !== undefined) {
+    updates.push("password_hash = ?");
+    binds.push(await hashPassword(input.password));
+  }
+  if (input.isDisabled !== undefined) {
+    updates.push("is_disabled = ?");
+    binds.push(input.isDisabled ? 1 : 0);
+  }
+  updates.push("updated_at = ?");
+  binds.push(isoNow(), userId);
+
+  const statements = [
+    c.env.DB.prepare(`UPDATE users SET ${updates.join(", ")} WHERE id = ?`).bind(...binds),
+    auditStatement(c.env.DB, "user", c.get("auth").actorId, "user.update", "user", userId, {
+      passwordReset: input.password !== undefined,
+      isDisabled: input.isDisabled,
+    }),
+  ];
+  if (input.password !== undefined || input.isDisabled === true) {
+    statements.push(c.env.DB.prepare(`UPDATE sessions SET revoked_at = ? WHERE user_id = ? AND revoked_at IS NULL`).bind(isoNow(), userId));
+  }
+  await c.env.DB.batch(statements);
+
+  const user = await getInstanceUser(c.env.DB, userId);
+  return c.json({ user: user ? mapInstanceUser(user) : null });
+});
+
 app.post("/api/v1/auth/logout", async (c) => {
   const token = getCookie(c, SESSION_COOKIE) ?? getBearerToken(c);
 
@@ -542,6 +662,8 @@ app.use("/api/v1/*", async (c, next) => {
       username: "owner",
       displayName: "Owner",
       scopes: [],
+      workspaceId: DEFAULT_WORKSPACE_ID,
+      role: "owner",
     });
     await next();
     return;
@@ -565,11 +687,12 @@ app.get("/api/v1/api-tokens", async (c) => {
   }
 
   const rows = await c.env.DB.prepare(
-    `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at
+    `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at, workspace_id
      FROM api_tokens
+     WHERE workspace_id = ?
      ORDER BY is_revoked ASC, created_at DESC
      LIMIT 200`
-  ).all<ApiTokenRow>();
+  ).bind(getWorkspaceId(c)).all<ApiTokenRow>();
 
   return c.json({
     apiTokens: rows.results.map(mapApiToken),
@@ -598,9 +721,9 @@ app.post("/api/v1/api-tokens", zValidator("json", ApiTokenCreateSchema), async (
 
   await c.env.DB.batch([
     c.env.DB.prepare(
-      `INSERT INTO api_tokens (id, name, token_hash, token_value, scopes_json, expires_at, created_at)
-       VALUES (?, ?, ?, ?, ?, ?, ?)`
-    ).bind(id, input.name, await sha256(token), token, JSON.stringify(scopes), input.expiresAt ?? null, now),
+      `INSERT INTO api_tokens (id, workspace_id, name, token_hash, token_value, scopes_json, expires_at, created_at)
+       VALUES (?, ?, ?, ?, ?, ?, ?, ?)`
+    ).bind(id, getWorkspaceId(c), input.name, await sha256(token), token, JSON.stringify(scopes), input.expiresAt ?? null, now),
     auditStatement(c.env.DB, actor.actorType, actor.actorId, "api_token.create", "api_token", id, {
       name: input.name,
       scopes,
@@ -608,7 +731,7 @@ app.post("/api/v1/api-tokens", zValidator("json", ApiTokenCreateSchema), async (
     }),
   ]);
 
-  const row = await getApiTokenRow(c.env.DB, id);
+  const row = await getApiTokenRow(c.env.DB, id, getWorkspaceId(c));
 
   if (!row) {
     return notFound(c, "API token not found");
@@ -628,7 +751,7 @@ app.delete("/api/v1/api-tokens/:id", async (c) => {
   const actor = getAuditActor(c);
 
   await c.env.DB.batch([
-    c.env.DB.prepare(`DELETE FROM api_tokens WHERE id = ?`).bind(id),
+    c.env.DB.prepare(`DELETE FROM api_tokens WHERE id = ? AND workspace_id = ?`).bind(id, getWorkspaceId(c)),
     auditStatement(c.env.DB, actor.actorType, actor.actorId, "api_token.delete", "api_token", id, {}),
   ]);
 
@@ -648,11 +771,11 @@ app.get("/api/v1/notebooks", async (c) => {
 
   const rows = await c.env.DB.prepare(
     notebookSelectSql(
-      `WHERE n.is_deleted = 0
+      `WHERE n.workspace_id = ? AND n.is_deleted = 0
        GROUP BY n.id, n.parent_id, n.name, n.slug, n.icon, n.color, n.sort_order, n.created_at, n.updated_at
        ORDER BY n.parent_id IS NOT NULL, n.sort_order ASC, n.name ASC`
     )
-  ).all<NotebookRow>();
+  ).bind(getWorkspaceId(c)).all<NotebookRow>();
 
   return c.json({ notebooks: rows.results.map(mapNotebook) });
 });
@@ -668,7 +791,7 @@ app.post("/api/v1/notebooks", zValidator("json", NotebookCreateSchema), async (c
   const actor = getAuditActor(c);
 
   try {
-    const notebook = await createNotebookRecord(c.env.DB, input, actor);
+    const notebook = await createNotebookRecord(c.env.DB, getWorkspaceId(c), input, actor);
     return c.json({ notebook }, 201);
   } catch (error) {
     if (error instanceof AppError) {
@@ -691,7 +814,7 @@ app.patch("/api/v1/notebooks/:id", zValidator("json", NotebookUpdateSchema), asy
   const actor = getAuditActor(c);
 
   try {
-    const notebook = await updateNotebookRecord(c.env.DB, id, input, actor);
+    const notebook = await updateNotebookRecord(c.env.DB, getWorkspaceId(c), id, input, actor);
     return c.json({ notebook });
   } catch (error) {
     if (error instanceof AppError) {
@@ -712,7 +835,8 @@ app.delete("/api/v1/notebooks/:id", async (c) => {
   const id = c.req.param("id");
   const actor = getAuditActor(c);
   const now = isoNow();
-  const current = await getNotebook(c.env.DB, id);
+  const workspaceId = getWorkspaceId(c);
+  const current = await getNotebook(c.env.DB, workspaceId, id);
 
   if (!current) {
     return notFound(c, "Notebook not found");
@@ -723,11 +847,11 @@ app.delete("/api/v1/notebooks/:id", async (c) => {
   }
 
   const [childCount, memoCount] = await Promise.all([
-    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM notebooks WHERE parent_id = ? AND is_deleted = 0`)
-      .bind(id)
+    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM notebooks WHERE workspace_id = ? AND parent_id = ? AND is_deleted = 0`)
+      .bind(workspaceId, id)
       .first<{ count: number }>(),
-    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE notebook_id = ? AND is_deleted = 0`)
-      .bind(id)
+    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE workspace_id = ? AND notebook_id = ? AND is_deleted = 0`)
+      .bind(workspaceId, id)
       .first<{ count: number }>(),
   ]);
 
@@ -738,9 +862,9 @@ app.delete("/api/v1/notebooks/:id", async (c) => {
   await c.env.DB.prepare(
     `UPDATE notebooks
      SET is_deleted = 1, deleted_at = ?, updated_at = ?
-     WHERE id = ? AND id <> 'nb_inbox'`
+     WHERE id = ? AND workspace_id = ? AND slug <> 'inbox'`
   )
-    .bind(now, now, id)
+    .bind(now, now, id, workspaceId)
     .run();
 
   await audit(c.env.DB, actor.actorType, actor.actorId, "notebook.delete", "notebook", id, {});
@@ -754,7 +878,7 @@ app.get("/api/v1/tags", async (c) => {
     return denied;
   }
 
-  return c.json({ tags: await listTagSummaries(c.env.DB) });
+  return c.json({ tags: await listTagSummaries(c.env.DB, getWorkspaceId(c)) });
 });
 
 app.patch("/api/v1/tags/:tag", zValidator("json", TagRenameSchema), async (c) => {
@@ -768,7 +892,7 @@ app.patch("/api/v1/tags/:tag", zValidator("json", TagRenameSchema), async (c) =>
   const input = c.req.valid("json");
   const actor = getAuditActor(c);
   const actorLabel = getActorLabel(c);
-  const updated = await updateTagAcrossMemos(c.env.DB, oldTag, input.name, actor, actorLabel);
+  const updated = await updateTagAcrossMemos(c.env.DB, getWorkspaceId(c), oldTag, input.name, actor, actorLabel);
 
   return c.json({ ok: true, updated });
 });
@@ -783,7 +907,7 @@ app.delete("/api/v1/tags/:tag", async (c) => {
   const tag = decodeTagParam(c.req.param("tag"));
   const actor = getAuditActor(c);
   const actorLabel = getActorLabel(c);
-  const updated = await updateTagAcrossMemos(c.env.DB, tag, null, actor, actorLabel);
+  const updated = await updateTagAcrossMemos(c.env.DB, getWorkspaceId(c), tag, null, actor, actorLabel);
 
   return c.json({ ok: true, updated });
 });
@@ -804,8 +928,8 @@ app.get("/api/v1/memos", async (c) => {
   const cursor = decodeMemoListCursor(c.req.query("cursor"), sort);
   const deletedClause = includeTrash ? "m.is_deleted = 1" : "m.is_deleted = 0";
   const titleSortExpression = `LOWER(COALESCE(NULLIF(m.title, ''), '${UNTITLED_MEMO_TITLE}'))`;
-  const baseConditions = [deletedClause];
-  const baseBinds: unknown[] = [];
+  const baseConditions = ["m.workspace_id = ?", deletedClause];
+  const baseBinds: unknown[] = [getWorkspaceId(c)];
 
   if (notebookId) {
     baseConditions.push("m.notebook_id = ?");
@@ -1019,9 +1143,9 @@ app.post("/api/v1/memos", zValidator("json", MemoCreateSchema), async (c) => {
   await c.env.DB.batch([
     c.env.DB.prepare(
       `INSERT INTO memos (
-        id, notebook_id, title, excerpt, tags_json, created_by, updated_by, created_at, updated_at
-      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`
-    ).bind(id, input.notebookId, title, excerpt, JSON.stringify(tags), actorLabel, actorLabel, createdAt, updatedAt),
+        id, workspace_id, notebook_id, title, excerpt, tags_json, created_by, updated_by, created_at, updated_at
+      ) SELECT ?, ?, id, ?, ?, ?, ?, ?, ?, ? FROM notebooks WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
+    ).bind(id, getWorkspaceId(c), title, excerpt, JSON.stringify(tags), actorLabel, actorLabel, createdAt, updatedAt, input.notebookId, getWorkspaceId(c)),
     c.env.DB.prepare(
       `INSERT INTO memo_contents (
         memo_id, content_json, content_markdown, content_text, content_hash, revision, created_at, updated_at
@@ -1036,7 +1160,7 @@ app.post("/api/v1/memos", zValidator("json", MemoCreateSchema), async (c) => {
     }),
   ]);
 
-  return c.json({ memo: await getMemoDetail(c.env.DB, id) }, 201);
+  return c.json({ memo: await getMemoDetail(c.env.DB, getWorkspaceId(c), id) }, 201);
 });
 
 app.post("/api/v1/memos/batch/move", zValidator("json", MoveMemosSchema), async (c) => {
@@ -1047,7 +1171,7 @@ app.post("/api/v1/memos/batch/move", zValidator("json", MoveMemosSchema), async
   }
 
   const input = c.req.valid("json");
-  const target = await getNotebook(c.env.DB, input.notebookId);
+  const target = await getNotebook(c.env.DB, getWorkspaceId(c), input.notebookId);
 
   if (!target) {
     return notFound(c, "Target notebook not found");
@@ -1057,7 +1181,7 @@ app.post("/api/v1/memos/batch/move", zValidator("json", MoveMemosSchema), async
   const actorLabel = getActorLabel(c);
 
   try {
-    const moved = await moveMemosToNotebook(c.env.DB, input.memoIds, input.notebookId, actor, actorLabel);
+    const moved = await moveMemosToNotebook(c.env.DB, getWorkspaceId(c), input.memoIds, input.notebookId, actor, actorLabel);
 
     return c.json({ ok: true, moved });
   } catch (error) {
@@ -1080,7 +1204,7 @@ app.post("/api/v1/memos/batch/delete", zValidator("json", DeleteMemosSchema), as
   const actor = getAuditActor(c);
 
   try {
-    const deleted = await deleteMemosRecord(c.env.DB, c.env.RESOURCES, input.memoIds, Boolean(input.permanent), actor);
+    const deleted = await deleteMemosRecord(c.env.DB, c.env.RESOURCES, getWorkspaceId(c), input.memoIds, Boolean(input.permanent), actor);
     return c.json({ ok: true, deleted });
   } catch (error) {
     if (error instanceof AppError) {
@@ -1099,7 +1223,7 @@ app.delete("/api/v1/memos/trash/empty", async (c) => {
   }
 
   const actor = getAuditActor(c);
-  const deleted = await emptyTrashMemosRecord(c.env.DB, c.env.RESOURCES, actor);
+  const deleted = await emptyTrashMemosRecord(c.env.DB, c.env.RESOURCES, getWorkspaceId(c), actor);
 
   return c.json({ ok: true, deleted });
 });
@@ -1112,7 +1236,7 @@ app.get("/api/v1/memos/:id", async (c) => {
   }
 
   const includeDeleted = c.req.query("includeDeleted") === "1";
-  const memo = await getMemoDetail(c.env.DB, c.req.param("id"), includeDeleted);
+  const memo = await getMemoDetail(c.env.DB, getWorkspaceId(c), c.req.param("id"), includeDeleted);
 
   if (!memo) {
     return notFound(c, "Memo not found");
@@ -1129,7 +1253,7 @@ app.post("/api/v1/memos/:id/edit-sessions", async (c) => {
   }
 
   const memoId = c.req.param("id");
-  const current = await getMemoDetailRow(c.env.DB, memoId);
+  const current = await getMemoDetailRow(c.env.DB, getWorkspaceId(c), memoId);
 
   if (!current) {
     return notFound(c, "Memo not found");
@@ -1176,7 +1300,7 @@ app.get("/api/v1/memos/:id/revisions", async (c) => {
   }
 
   const memoId = c.req.param("id");
-  const memo = await getMemoDetail(c.env.DB, memoId);
+  const memo = await getMemoDetail(c.env.DB, getWorkspaceId(c), memoId);
 
   if (!memo) {
     return notFound(c, "Memo not found");
@@ -1208,13 +1332,13 @@ app.post("/api/v1/memos/:id/revisions/:revisionId/restore", async (c) => {
   const revisionId = c.req.param("revisionId");
   const actor = getAuditActor(c);
   const actorLabel = getActorLabel(c);
-  const current = await getMemoDetailRow(c.env.DB, memoId);
+  const current = await getMemoDetailRow(c.env.DB, getWorkspaceId(c), memoId);
 
   if (!current) {
     return notFound(c, "Memo not found");
   }
 
-  const revision = await getMemoRevisionRow(c.env.DB, memoId, revisionId);
+  const revision = await getMemoRevisionRow(c.env.DB, getWorkspaceId(c), memoId, revisionId);
 
   if (!revision) {
     return notFound(c, "Memo revision not found");
@@ -1255,7 +1379,7 @@ app.post("/api/v1/memos/:id/revisions/:revisionId/restore", async (c) => {
     }),
   ]);
 
-  return c.json({ memo: await getMemoDetail(c.env.DB, memoId) });
+  return c.json({ memo: await getMemoDetail(c.env.DB, getWorkspaceId(c), memoId) });
 });
 
 app.get("/api/v1/exports/markdown", async (c) => {
@@ -1275,13 +1399,13 @@ app.get("/api/v1/exports/markdown", async (c) => {
               m.source_memo_ids, m.merge_source_count, m.merged_into_memo_id
        FROM memos m
        INNER JOIN memo_contents mc ON mc.memo_id = m.id
-       WHERE m.is_deleted = 0
+       WHERE m.workspace_id = ? AND m.is_deleted = 0
        ORDER BY m.created_at ASC, m.id ASC
        LIMIT ? OFFSET ?`
     )
-      .bind(limit, offset)
+      .bind(getWorkspaceId(c), limit, offset)
       .all<MemoDetailRow>(),
-    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE is_deleted = 0`).first<{ count: number }>(),
+    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE workspace_id = ? AND is_deleted = 0`).bind(getWorkspaceId(c)).first<{ count: number }>(),
   ]);
 
   const memoIds = memoRows.results.map((row) => row.id);
@@ -1290,8 +1414,8 @@ app.get("/api/v1/exports/markdown", async (c) => {
   if (memoIds.length > 0) {
     const placeholders = memoIds.map(() => "?").join(", ");
     const resourceRows = await c.env.DB.prepare(
-      `SELECT id, memo_id, original_memo_id, bucket_name, object_key, kind, mime_type,
-              filename, byte_size, sha256, width, height, created_at, updated_at
+      `SELECT r.id, r.memo_id, r.original_memo_id, r.bucket_name, r.object_key, r.kind, r.mime_type,
+              r.filename, r.byte_size, r.sha256, r.width, r.height, r.created_at, r.updated_at
        FROM resources
        WHERE is_deleted = 0 AND memo_id IN (${placeholders})
        ORDER BY memo_id ASC, created_at ASC, id ASC`
@@ -1329,13 +1453,13 @@ app.get("/api/v1/backups/json", async (c) => {
               m.source_memo_ids, m.merge_source_count, m.merged_into_memo_id
        FROM memos m
        INNER JOIN memo_contents mc ON mc.memo_id = m.id
-       WHERE m.is_deleted = 0
+       WHERE m.workspace_id = ? AND m.is_deleted = 0
        ORDER BY m.created_at ASC, m.id ASC
        LIMIT ? OFFSET ?`
     )
-      .bind(limit, offset)
+      .bind(getWorkspaceId(c), limit, offset)
       .all<MemoDetailRow>(),
-    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE is_deleted = 0`).first<{ count: number }>(),
+    c.env.DB.prepare(`SELECT COUNT(*) AS count FROM memos WHERE workspace_id = ? AND is_deleted = 0`).bind(getWorkspaceId(c)).first<{ count: number }>(),
   ]);
   const memoIds = memoRows.results.map((row) => row.id);
   let resources: Resource[] = [];
@@ -1385,7 +1509,7 @@ app.post("/api/v1/restores/json/notebooks", zValidator("json", RestoreJsonNotebo
     return userOnly;
   }
 
-  await restoreJsonNotebooks(c.env.DB, c.req.valid("json").notebooks as JsonBackupNotebook[]);
+  await restoreJsonNotebooks(c.env.DB, getWorkspaceId(c), c.req.valid("json").notebooks as JsonBackupNotebook[]);
   return c.json({ ok: true });
 });
 
@@ -1395,7 +1519,7 @@ app.post("/api/v1/restores/json/memos", zValidator("json", RestoreJsonMemosSchem
     return userOnly;
   }
 
-  await restoreJsonMemos(c.env.DB, c.req.valid("json").memos as JsonBackupMemo[]);
+  await restoreJsonMemos(c.env.DB, getWorkspaceId(c), c.req.valid("json").memos as JsonBackupMemo[]);
   return c.json({ ok: true });
 });
 
@@ -1425,7 +1549,7 @@ app.put("/api/v1/restores/json/resources/:id", async (c) => {
   }
 
   const metadata = parsed.data as JsonBackupResource;
-  const memo = await getMemoDetail(c.env.DB, metadata.memoId);
+  const memo = await getMemoDetail(c.env.DB, getWorkspaceId(c), metadata.memoId);
   if (!memo) {
     return notFound(c, "Restore target memo not found.");
   }
@@ -1436,13 +1560,20 @@ app.put("/api/v1/restores/json/resources/:id", async (c) => {
   }
 
   const filename = normalizeFilename(metadata.filename || file.name) || `${metadata.kind}-${metadata.id}`;
-  const objectKey = `restores/${metadata.memoId}/${metadata.id}/${Date.now()}-${filename}`;
+  const objectKey = `workspaces/${getWorkspaceId(c)}/restores/${metadata.memoId}/${metadata.id}/${Date.now()}-${filename}`;
   const bytes = new Uint8Array(await file.arrayBuffer());
+  const foreignResource = await c.env.DB.prepare(
+    `SELECT r.id FROM resources r INNER JOIN memos m ON m.id = r.memo_id
+     WHERE r.id = ? AND m.workspace_id <> ? LIMIT 1`
+  ).bind(metadata.id, getWorkspaceId(c)).first<{ id: string }>();
+  if (foreignResource) {
+    return conflict(c, "cross_workspace_id_conflict", "Backup resource ID is already used by another user.");
+  }
   const previous = await c.env.DB.prepare(
-    `SELECT object_key FROM resources WHERE id = ?`
-  ).bind(metadata.id).first<{ object_key: string }>();
+    `SELECT r.object_key FROM resources r INNER JOIN memos m ON m.id = r.memo_id WHERE r.id = ? AND m.workspace_id = ?`
+  ).bind(metadata.id, getWorkspaceId(c)).first<{ object_key: string }>();
   const originalMemo = metadata.originalMemoId
-    ? await c.env.DB.prepare(`SELECT id FROM memos WHERE id = ?`).bind(metadata.originalMemoId).first<{ id: string }>()
+    ? await c.env.DB.prepare(`SELECT id FROM memos WHERE id = ? AND workspace_id = ?`).bind(metadata.originalMemoId, getWorkspaceId(c)).first<{ id: string }>()
     : null;
 
   await c.env.RESOURCES.put(objectKey, bytes, {
@@ -1517,21 +1648,22 @@ app.get("/api/v1/resources", async (c) => {
               r.created_at, r.updated_at, m.title AS memo_title, m.excerpt AS memo_excerpt,
               m.is_deleted AS memo_is_deleted
        FROM resources r
-       LEFT JOIN memos m ON m.id = r.memo_id
-       WHERE r.is_deleted = 0
+       INNER JOIN memos m ON m.id = r.memo_id
+       WHERE m.workspace_id = ? AND r.is_deleted = 0
        ORDER BY r.created_at DESC
        LIMIT ?`
     )
-      .bind(limit)
+      .bind(getWorkspaceId(c), limit)
       .all<ResourceListRow>(),
     c.env.DB.prepare(
       `SELECT COUNT(*) AS total_count,
               COALESCE(SUM(byte_size), 0) AS total_bytes,
               COALESCE(SUM(CASE WHEN kind = 'image' THEN 1 ELSE 0 END), 0) AS image_count,
               COALESCE(SUM(CASE WHEN kind = 'attachment' THEN 1 ELSE 0 END), 0) AS attachment_count
-       FROM resources
-       WHERE is_deleted = 0`
-    ).first<ResourceStatsRow>(),
+       FROM resources r
+       INNER JOIN memos m ON m.id = r.memo_id
+       WHERE m.workspace_id = ? AND r.is_deleted = 0`
+    ).bind(getWorkspaceId(c)).first<ResourceStatsRow>(),
   ]);
 
   return c.json({
@@ -1548,7 +1680,7 @@ app.post("/api/v1/memos/:id/resources", async (c) => {
   }
 
   const memoId = c.req.param("id");
-  const memo = await getMemoDetail(c.env.DB, memoId);
+  const memo = await getMemoDetail(c.env.DB, getWorkspaceId(c), memoId);
 
   if (!memo) {
     return notFound(c, "Memo not found");
@@ -1615,7 +1747,7 @@ const createImageResource = async (
     mimeType: input.mimeType,
     source: input.source,
   });
-  const objectKey = `memos/${input.memoId}/${resourceId}${inferImageExtension(processed.filename, processed.mimeType)}`;
+  const objectKey = `workspaces/${getWorkspaceId(c)}/memos/${input.memoId}/${resourceId}${inferImageExtension(processed.filename, processed.mimeType)}`;
   const bucketName = c.env.EDGE_EVER_R2_BUCKET_NAME?.trim() || DEFAULT_R2_BUCKET_NAME;
   const filename = normalizeFilename(processed.filename) || `${resourceId}${inferImageExtension(processed.filename, processed.mimeType)}`;
   const checksum = await sha256Bytes(processed.bytes);
@@ -1666,7 +1798,7 @@ const createImageResource = async (
     throw error;
   }
 
-  const resource = await getResourceRow(c.env.DB, resourceId);
+  const resource = await getResourceRow(c.env.DB, getWorkspaceId(c), resourceId);
 
   if (!resource) {
     throw new AppError("not_found", "Resource not found", 404);
@@ -1690,7 +1822,7 @@ const createAttachmentResource = async (
   const resourceId = createId("res");
   const now = isoNow();
   const filename = normalizeFilename(input.filename) || resourceId;
-  const objectKey = `memos/${input.memoId}/${resourceId}`;
+  const objectKey = `workspaces/${getWorkspaceId(c)}/memos/${input.memoId}/${resourceId}`;
   const bucketName = c.env.EDGE_EVER_R2_BUCKET_NAME?.trim() || DEFAULT_R2_BUCKET_NAME;
   const checksum = await sha256Bytes(input.bytes);
 
@@ -1737,7 +1869,7 @@ const createAttachmentResource = async (
     throw error;
   }
 
-  const resource = await getResourceRow(c.env.DB, resourceId);
+  const resource = await getResourceRow(c.env.DB, getWorkspaceId(c), resourceId);
 
   if (!resource) {
     throw new AppError("not_found", "Resource not found", 404);
@@ -1800,7 +1932,7 @@ app.get("/api/v1/resources/:id/blob", async (c) => {
     return denied;
   }
 
-  const resource = await getResourceRow(c.env.DB, c.req.param("id"));
+  const resource = await getResourceRow(c.env.DB, getWorkspaceId(c), c.req.param("id"));
 
   if (!resource) {
     return notFound(c, "Resource not found");
@@ -1846,7 +1978,8 @@ app.post("/api/v1/memos/:id/save", zValidator("json", MemoUpdateSchema), async (
 const updateMemoFromInput = async (c: AppContext, id: string, input: MemoUpdateInput) => {
   const actor = getAuditActor(c);
   const actorLabel = getActorLabel(c);
-  const current = await getMemoDetailRow(c.env.DB, id);
+  const workspaceId = getWorkspaceId(c);
+  const current = await getMemoDetailRow(c.env.DB, workspaceId, id);
 
   if (!current) {
     return notFound(c, "Memo not found");
@@ -1933,7 +2066,7 @@ const updateMemoFromInput = async (c: AppContext, id: string, input: MemoUpdateI
 
   if (!hasContentUpdate) {
     if (input.isPinned === undefined || isPinned === Boolean(current.is_pinned)) {
-      return c.json({ memo: await getMemoDetail(c.env.DB, id) });
+      return c.json({ memo: await getMemoDetail(c.env.DB, workspaceId, id) });
     }
 
     await c.env.DB.batch([
@@ -1945,7 +2078,7 @@ const updateMemoFromInput = async (c: AppContext, id: string, input: MemoUpdateI
       auditStatement(c.env.DB, actor.actorType, actor.actorId, isPinned ? "memo.pin" : "memo.unpin", "memo", id, {}),
     ]);
 
-    return c.json({ memo: await getMemoDetail(c.env.DB, id) });
+    return c.json({ memo: await getMemoDetail(c.env.DB, workspaceId, id) });
   }
 
   const currentContentJson = JSON.parse(current.content_json) as TiptapDoc;
@@ -2013,8 +2146,9 @@ const updateMemoFromInput = async (c: AppContext, id: string, input: MemoUpdateI
     c.env.DB.prepare(
       `UPDATE memos
        SET notebook_id = ?, title = ?, excerpt = ?, tags_json = ?, is_pinned = ?, updated_by = ?, updated_at = ?, created_at = COALESCE(?, created_at)
-       WHERE id = ? AND is_deleted = 0`
-    ).bind(notebookId, title, excerpt, JSON.stringify(tags), isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id),
+       WHERE id = ? AND workspace_id = ? AND is_deleted = 0
+         AND EXISTS (SELECT 1 FROM notebooks n WHERE n.id = ? AND n.workspace_id = ? AND n.is_deleted = 0)`
+    ).bind(notebookId, title, excerpt, JSON.stringify(tags), isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id, workspaceId, notebookId, workspaceId),
     c.env.DB.prepare(
       `UPDATE memo_contents
        SET content_json = ?, content_markdown = ?, content_text = ?, content_hash = ?,
@@ -2032,7 +2166,7 @@ const updateMemoFromInput = async (c: AppContext, id: string, input: MemoUpdateI
     }),
   ]);
 
-  return c.json({ memo: await getMemoDetail(c.env.DB, id) });
+  return c.json({ memo: await getMemoDetail(c.env.DB, workspaceId, id) });
 };
 
 app.delete("/api/v1/memos/:id", async (c) => {
@@ -2046,15 +2180,16 @@ app.delete("/api/v1/memos/:id", async (c) => {
   const actor = getAuditActor(c);
   const permanent = c.req.query("permanent") === "1";
   const now = isoNow();
+  const workspaceId = getWorkspaceId(c);
 
   if (permanent) {
-    const current = await getMemoDetailRow(c.env.DB, id, true);
+    const current = await getMemoDetailRow(c.env.DB, workspaceId, id, true);
 
     if (!current || current.is_deleted === 0) {
       return notFound(c, "Memo not found in trash");
     }
 
-    const resources = await getResourceRowsForMemo(c.env.DB, id);
+    const resources = await getResourceRowsForMemo(c.env.DB, workspaceId, id);
 
     if (resources.length > 0) {
       await c.env.RESOURCES.delete(resources.map((resource) => resource.object_key));
@@ -2065,7 +2200,7 @@ app.delete("/api/v1/memos/:id", async (c) => {
       c.env.DB.prepare(`DELETE FROM resources WHERE memo_id = ?`).bind(id),
       c.env.DB.prepare(`DELETE FROM memo_revisions WHERE memo_id = ?`).bind(id),
       c.env.DB.prepare(`DELETE FROM memo_contents WHERE memo_id = ?`).bind(id),
-      c.env.DB.prepare(`DELETE FROM memos WHERE id = ? AND is_deleted = 1`).bind(id),
+      c.env.DB.prepare(`DELETE FROM memos WHERE id = ? AND workspace_id = ? AND is_deleted = 1`).bind(id, workspaceId),
       auditStatement(c.env.DB, actor.actorType, actor.actorId, "memo.delete_permanent", "memo", id, {}),
     ]);
 
@@ -2076,8 +2211,8 @@ app.delete("/api/v1/memos/:id", async (c) => {
     c.env.DB.prepare(
       `UPDATE memos
        SET is_deleted = 1, deleted_at = ?, updated_at = ?
-       WHERE id = ? AND is_deleted = 0`
-    ).bind(now, now, id),
+       WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
+    ).bind(now, now, id, workspaceId),
     c.env.DB.prepare(
       `UPDATE resources
        SET is_deleted = 1, deleted_at = ?, updated_at = ?
@@ -2099,7 +2234,8 @@ app.post("/api/v1/memos/:id/restore", async (c) => {
 
   const id = c.req.param("id");
   const actor = getAuditActor(c);
-  const current = await getMemoDetailRow(c.env.DB, id, true);
+  const workspaceId = getWorkspaceId(c);
+  const current = await getMemoDetailRow(c.env.DB, workspaceId, id, true);
 
   if (!current || current.is_deleted === 0) {
     return notFound(c, "Memo not found in trash");
@@ -2107,10 +2243,11 @@ app.post("/api/v1/memos/:id/restore", async (c) => {
 
   const tags = parseJsonArray(current.tags_json);
   const now = isoNow();
-  const originalNotebook = await getNotebook(c.env.DB, current.notebook_id);
-  const restoreNotebookId = originalNotebook ? current.notebook_id : "nb_inbox";
+  const originalNotebook = await getNotebook(c.env.DB, workspaceId, current.notebook_id);
+  const inbox = await c.env.DB.prepare(`SELECT id FROM notebooks WHERE workspace_id = ? AND slug = 'inbox' AND is_deleted = 0 LIMIT 1`).bind(workspaceId).first<{ id: string }>();
+  const restoreNotebookId = originalNotebook ? current.notebook_id : inbox?.id;
 
-  if (!originalNotebook && !(await getNotebook(c.env.DB, restoreNotebookId))) {
+  if (!restoreNotebookId) {
     return conflict(c, "restore_notebook_missing", "Original notebook was deleted and the default inbox is unavailable.");
   }
 
@@ -2118,8 +2255,8 @@ app.post("/api/v1/memos/:id/restore", async (c) => {
     c.env.DB.prepare(
       `UPDATE memos
        SET notebook_id = ?, is_deleted = 0, deleted_at = NULL, updated_at = ?
-       WHERE id = ? AND is_deleted = 1`
-    ).bind(restoreNotebookId, now, id),
+       WHERE id = ? AND workspace_id = ? AND is_deleted = 1`
+    ).bind(restoreNotebookId, now, id, workspaceId),
     c.env.DB.prepare(
       `UPDATE resources
        SET is_deleted = 0, deleted_at = NULL, updated_at = ?
@@ -2136,7 +2273,7 @@ app.post("/api/v1/memos/:id/restore", async (c) => {
     }),
   ]);
 
-  return c.json({ memo: await getMemoDetail(c.env.DB, id) });
+  return c.json({ memo: await getMemoDetail(c.env.DB, workspaceId, id) });
 });
 
 app.post("/api/v1/memos/merge", zValidator("json", MergeMemosSchema), async (c) => {
@@ -2151,7 +2288,7 @@ app.post("/api/v1/memos/merge", zValidator("json", MergeMemosSchema), async (c)
   const actorLabel = getActorLabel(c);
 
   try {
-    const memo = await mergeMemosRecord(c.env.DB, input, actor, actorLabel);
+    const memo = await mergeMemosRecord(c.env.DB, getWorkspaceId(c), input, actor, actorLabel);
     return c.json({ memo }, 201);
   } catch (error) {
     if (error instanceof AppError) {
@@ -2733,6 +2870,7 @@ const callMcpTool = async (
       assertScope(auth, "read:memos");
       return {
         memos: await searchMemoSummaries(c.env.DB, {
+          workspaceId: auth.workspaceId,
           query: getOptionalString(args.query),
           notebookId: getOptionalString(args.notebookId),
           tags: getOptionalStringArray(args.tags),
@@ -2749,6 +2887,7 @@ const callMcpTool = async (
     case "list_memos": {
       assertScope(auth, "read:memos");
       return await listMemosForMcp(c.env.DB, {
+        workspaceId: auth.workspaceId,
         notebookId: getOptionalString(args.notebookId),
         limit: clampNumber(Number(args.limit ?? 50), 1, 100),
         offset: clampNumber(Number(args.offset ?? 0), 0, 100_000),
@@ -2759,7 +2898,7 @@ const callMcpTool = async (
     case "get_memo": {
       assertScope(auth, "read:memos");
       const memoId = getRequiredString(args.memoId, "memoId");
-      const memo = await getMemoDetail(c.env.DB, memoId, args.includeDeleted === true);
+      const memo = await getMemoDetail(c.env.DB, auth.workspaceId, memoId, args.includeDeleted === true);
 
       if (!memo) {
         throw new Error("Memo not found");
@@ -2772,7 +2911,7 @@ const callMcpTool = async (
       const notebookId = getRequiredString(args.notebookId, "notebookId");
       const actor = getAuditActor(c);
       const actorLabel = getActorLabel(c);
-      const memo = await createMemoRecord(c.env.DB, {
+      const memo = await createMemoRecord(c.env.DB, auth.workspaceId, {
         notebookId,
         title: getOptionalString(args.title) ?? undefined,
         contentMarkdown: getOptionalString(args.contentMarkdown) ?? "",
@@ -2790,6 +2929,7 @@ const callMcpTool = async (
       const actorLabel = getActorLabel(c);
       const result = await updateMemoRecord(
         c.env.DB,
+        auth.workspaceId,
         memoId,
         {
           expectedRevision:
@@ -2819,10 +2959,10 @@ const callMcpTool = async (
       const memoIds = getRequiredStringArray(args.memoIds, "memoIds");
 
       if (args.dryRun === true) {
-        return { dryRun: true, memos: await getMemosForBulkAction(c.env.DB, memoIds, 0) };
+        return { dryRun: true, memos: await getMemosForBulkAction(c.env.DB, auth.workspaceId, memoIds, 0) };
       }
 
-      const deleted = await deleteMemosRecord(c.env.DB, c.env.RESOURCES, memoIds, false, getAuditActor(c));
+      const deleted = await deleteMemosRecord(c.env.DB, c.env.RESOURCES, auth.workspaceId, memoIds, false, getAuditActor(c));
       return { ok: true, deleted };
     }
     case "restore_memos": {
@@ -2830,16 +2970,16 @@ const callMcpTool = async (
       const memoIds = getRequiredStringArray(args.memoIds, "memoIds");
 
       if (args.dryRun === true) {
-        return { dryRun: true, memos: await getMemosForBulkAction(c.env.DB, memoIds, 1) };
+        return { dryRun: true, memos: await getMemosForBulkAction(c.env.DB, auth.workspaceId, memoIds, 1) };
       }
 
-      const restored = await restoreMemosRecord(c.env.DB, memoIds, getAuditActor(c));
+      const restored = await restoreMemosRecord(c.env.DB, auth.workspaceId, memoIds, getAuditActor(c));
       return { ok: true, restored };
     }
     case "upload_memo_image": {
       assertScope(auth, "write:resources");
       const memoId = getRequiredString(args.memoId, "memoId");
-      const memo = await getMemoDetail(c.env.DB, memoId);
+      const memo = await getMemoDetail(c.env.DB, auth.workspaceId, memoId);
 
       if (!memo) {
         throw new AppError("not_found", "Memo not found", 404);
@@ -2867,25 +3007,26 @@ const callMcpTool = async (
       assertScope(auth, "write:memos");
       const notebookId = getRequiredString(args.notebookId, "notebookId");
       const memoIds = getRequiredStringArray(args.memoIds, "memoIds");
-      const target = await getNotebook(c.env.DB, notebookId);
+      const target = await getNotebook(c.env.DB, auth.workspaceId, notebookId);
 
       if (!target) {
         throw new AppError("not_found", "Target notebook not found", 404);
       }
 
       if (args.dryRun === true) {
-        return { dryRun: true, targetNotebook: target, memos: await getMemosForBulkAction(c.env.DB, memoIds, 0) };
+        return { dryRun: true, targetNotebook: target, memos: await getMemosForBulkAction(c.env.DB, auth.workspaceId, memoIds, 0) };
       }
 
       const actor = getAuditActor(c);
       const actorLabel = getActorLabel(c);
-      const moved = await moveMemosToNotebook(c.env.DB, memoIds, notebookId, actor, actorLabel);
+      const moved = await moveMemosToNotebook(c.env.DB, auth.workspaceId, memoIds, notebookId, actor, actorLabel);
 
       return { ok: true, moved };
     }
     case "add_tags_to_memos": {
       assertScope(auth, "write:tags");
       return await updateTagsForMemos(c.env.DB, {
+        workspaceId: auth.workspaceId,
         memoIds: getRequiredStringArray(args.memoIds, "memoIds"),
         tags: getRequiredStringArray(args.tags, "tags"),
         mode: "add",
@@ -2897,6 +3038,7 @@ const callMcpTool = async (
     case "remove_tags_from_memos": {
       assertScope(auth, "write:tags");
       return await updateTagsForMemos(c.env.DB, {
+        workspaceId: auth.workspaceId,
         memoIds: getRequiredStringArray(args.memoIds, "memoIds"),
         tags: getRequiredStringArray(args.tags, "tags"),
         mode: "remove",
@@ -2911,10 +3053,10 @@ const callMcpTool = async (
       const to = getRequiredString(args.to, "to");
 
       if (args.dryRun === true) {
-        return await previewTagRename(c.env.DB, from, to);
+        return await previewTagRename(c.env.DB, auth.workspaceId, from, to);
       }
 
-      const updated = await updateTagAcrossMemos(c.env.DB, from, to, getAuditActor(c), getActorLabel(c));
+      const updated = await updateTagAcrossMemos(c.env.DB, auth.workspaceId, from, to, getAuditActor(c), getActorLabel(c));
       return { ok: true, updated };
     }
     case "delete_tag": {
@@ -2922,10 +3064,10 @@ const callMcpTool = async (
       const tag = getRequiredString(args.tag, "tag");
 
       if (args.dryRun === true) {
-        return await previewTagRename(c.env.DB, tag, null);
+        return await previewTagRename(c.env.DB, auth.workspaceId, tag, null);
       }
 
-      const updated = await updateTagAcrossMemos(c.env.DB, tag, null, getAuditActor(c), getActorLabel(c));
+      const updated = await updateTagAcrossMemos(c.env.DB, auth.workspaceId, tag, null, getAuditActor(c), getActorLabel(c));
       return { ok: true, updated };
     }
     case "merge_memos": {
@@ -2934,6 +3076,7 @@ const callMcpTool = async (
       const actorLabel = getActorLabel(c);
       const memo = await mergeMemosRecord(
         c.env.DB,
+        auth.workspaceId,
         {
           memoIds: getRequiredStringArray(args.memoIds, "memoIds"),
           notebookId: getOptionalString(args.notebookId) ?? undefined,
@@ -2948,7 +3091,7 @@ const callMcpTool = async (
     case "upload_memo_attachment": {
       assertScope(auth, "write:resources");
       const memoId = getRequiredString(args.memoId, "memoId");
-      const memo = await getMemoDetail(c.env.DB, memoId);
+      const memo = await getMemoDetail(c.env.DB, auth.workspaceId, memoId);
 
       if (!memo) {
         throw new AppError("not_found", "Memo not found", 404);
@@ -2973,23 +3116,24 @@ const callMcpTool = async (
     case "list_memo_resources": {
       assertScope(auth, "read:resources");
       const memoId = getRequiredString(args.memoId, "memoId");
-      const memo = await getMemoDetail(c.env.DB, memoId, true);
+      const memo = await getMemoDetail(c.env.DB, auth.workspaceId, memoId, true);
 
       if (!memo) {
         throw new AppError("not_found", "Memo not found", 404);
       }
 
-      return { resources: await listResourcesForMemo(c.env.DB, memoId) };
+      return { resources: await listResourcesForMemo(c.env.DB, auth.workspaceId, memoId) };
     }
     case "list_resources": {
       assertScope(auth, "read:resources");
-      return await listResourcesForMcp(c.env.DB, clampNumber(Number(args.limit ?? 100), 1, 500));
+      return await listResourcesForMcp(c.env.DB, auth.workspaceId, clampNumber(Number(args.limit ?? 100), 1, 500));
     }
     case "list_memo_revisions": {
       assertScope(auth, "read:memos");
       return {
         revisions: await listMemoRevisions(
           c.env.DB,
+          auth.workspaceId,
           getRequiredString(args.memoId, "memoId"),
           clampNumber(Number(args.limit ?? 50), 1, 100)
         ),
@@ -2999,7 +3143,7 @@ const callMcpTool = async (
       assertScope(auth, "write:memos");
       const memoId = getRequiredString(args.memoId, "memoId");
       const revisionId = getRequiredString(args.revisionId, "revisionId");
-      const revision = await getMemoRevisionRow(c.env.DB, memoId, revisionId);
+      const revision = await getMemoRevisionRow(c.env.DB, auth.workspaceId, memoId, revisionId);
 
       if (!revision) {
         throw new AppError("not_found", "Memo revision not found", 404);
@@ -3009,13 +3153,14 @@ const callMcpTool = async (
         return { dryRun: true, revision: mapMemoRevision(revision) };
       }
 
-      return { memo: await restoreMemoRevisionRecord(c.env.DB, memoId, revisionId, getAuditActor(c), getActorLabel(c)) };
+      return { memo: await restoreMemoRevisionRecord(c.env.DB, auth.workspaceId, memoId, revisionId, getAuditActor(c), getActorLabel(c)) };
     }
     case "move_notebook": {
       assertScope(auth, "write:notebooks");
       const actor = getAuditActor(c);
       const notebook = await updateNotebookRecord(
         c.env.DB,
+        auth.workspaceId,
         getRequiredString(args.notebookId, "notebookId"),
         {
           parentId: args.parentId === null ? null : getOptionalString(args.parentId) ?? undefined,
@@ -3037,6 +3182,7 @@ const callMcpTool = async (
 
       const notebook = await createNotebookRecord(
         c.env.DB,
+        auth.workspaceId,
         {
           name,
           parentId: args.parentId === null ? null : getOptionalString(args.parentId) ?? undefined,
@@ -3049,15 +3195,15 @@ const callMcpTool = async (
     }
     case "list_notebooks": {
       assertScope(auth, "read:notebooks");
-      return { notebooks: await listNotebooks(c.env.DB) };
+      return { notebooks: await listNotebooks(c.env.DB, auth.workspaceId) };
     }
     case "list_tags": {
       assertScope(auth, "read:tags");
-      return { tags: await listTagSummaries(c.env.DB) };
+      return { tags: await listTagSummaries(c.env.DB, auth.workspaceId) };
     }
     case "get_workspace_stats": {
       assertScope(auth, "read:memos");
-      return await getWorkspaceStats(c.env.DB);
+      return await getWorkspaceStats(c.env.DB, auth.workspaceId);
     }
     default:
       throw new Error(`Unknown tool: ${name}`);
@@ -3204,6 +3350,68 @@ const getUserByUsername = async (db: D1Database, username: string) =>
     .bind(username)
     .first<UserRow>();
 
+const getInstanceUser = (db: D1Database, userId: string) =>
+  db.prepare(
+    `SELECT u.id, u.username, u.password_hash, u.display_name, u.is_disabled,
+            u.last_login_at, u.created_at, wm.role
+     FROM users u
+     INNER JOIN workspace_members wm ON wm.user_id = u.id
+     WHERE u.id = ?`
+  ).bind(userId).first<InstanceUserRow>();
+
+const mapInstanceUser = (row: InstanceUserRow): InstanceUser => ({
+  id: row.id,
+  username: row.username,
+  displayName: row.display_name,
+  role: row.role,
+  isDisabled: Boolean(row.is_disabled),
+  lastLoginAt: row.last_login_at,
+  createdAt: row.created_at,
+});
+
+const ensureUserWorkspace = async (db: D1Database, userId: string, username: string) => {
+  const existing = await db.prepare(
+    `SELECT workspace_id, role FROM workspace_members WHERE user_id = ? LIMIT 1`
+  ).bind(userId).first<{ workspace_id: string; role: "owner" | "member" }>();
+  if (existing) return { workspaceId: existing.workspace_id, role: existing.role };
+
+  const defaultOwner = await db.prepare(
+    `SELECT user_id FROM workspace_members WHERE workspace_id = ? LIMIT 1`
+  ).bind(DEFAULT_WORKSPACE_ID).first<{ user_id: string }>();
+  if (!defaultOwner) {
+    await db.prepare(
+      `INSERT OR IGNORE INTO workspace_members (workspace_id, user_id, role) VALUES (?, ?, 'owner')`
+    ).bind(DEFAULT_WORKSPACE_ID, userId).run();
+    const claimed = await db.prepare(
+      `SELECT workspace_id, role FROM workspace_members WHERE user_id = ? LIMIT 1`
+    ).bind(userId).first<{ workspace_id: string; role: "owner" | "member" }>();
+    if (claimed) return { workspaceId: claimed.workspace_id, role: claimed.role };
+  }
+
+  const workspaceId = createId("ws");
+  const now = isoNow();
+  const notebooks = createDefaultNotebookRows(workspaceId, now);
+  await db.batch([
+    db.prepare(`INSERT INTO workspaces (id, name, is_personal, created_at, updated_at) VALUES (?, ?, 1, ?, ?)`)
+      .bind(workspaceId, `${username}'s workspace`, now, now),
+    db.prepare(`INSERT INTO workspace_members (workspace_id, user_id, role, created_at) VALUES (?, ?, 'member', ?)`)
+      .bind(workspaceId, userId, now),
+    ...notebooks.map((notebook) => db.prepare(
+      `INSERT INTO notebooks (id, workspace_id, parent_id, name, slug, icon, color, sort_order, created_at, updated_at)
+       VALUES (?, ?, NULL, ?, ?, 'notebook', ?, ?, ?, ?)`
+    ).bind(notebook.id, workspaceId, notebook.name, notebook.slug, notebook.color, notebook.sortOrder, now, now)),
+  ]);
+  return { workspaceId, role: "member" as const };
+};
+
+const createDefaultNotebookRows = (workspaceId: string, _now: string) => [
+  { id: `${workspaceId}_inbox`, name: "等待分类", slug: "inbox", color: "#0f766e", sortOrder: 10 },
+  { id: `${workspaceId}_projects`, name: "工作项目", slug: "work-projects", color: "#2563eb", sortOrder: 20 },
+  { id: `${workspaceId}_learning`, name: "学习资料", slug: "learning-resources", color: "#7c3aed", sortOrder: 30 },
+  { id: `${workspaceId}_creative`, name: "灵感创作", slug: "creative-ideas", color: "#db2777", sortOrder: 40 },
+  { id: `${workspaceId}_personal`, name: "生活个人", slug: "personal-life", color: "#ea580c", sortOrder: 50 },
+];
+
 const createSession = async (c: AppContext, user: UserRow) => {
   const token = randomToken(SESSION_TOKEN_BYTES);
   const id = createId("sess");
@@ -3274,7 +3482,7 @@ const authenticateBearerToken = async (c: AppContext, touch: boolean): Promise<A
   }
 
   const row = await c.env.DB.prepare(
-    `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at
+    `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at, workspace_id
      FROM api_tokens
      WHERE token_hash = ?
        AND is_revoked = 0
@@ -3298,6 +3506,8 @@ const authenticateBearerToken = async (c: AppContext, touch: boolean): Promise<A
     username: row.name,
     displayName: row.name,
     scopes: parseJsonArray(row.scopes_json),
+    workspaceId: row.workspace_id,
+    role: "member",
     tokenId: row.id,
   };
 };
@@ -3323,6 +3533,8 @@ const authenticateSessionToken = async (c: AppContext, token: string, touch: boo
     await c.env.DB.prepare(`UPDATE sessions SET last_seen_at = ? WHERE id = ?`).bind(isoNow(), row.id).run();
   }
 
+  const workspace = await ensureUserWorkspace(c.env.DB, row.user_id, row.username);
+
   return {
     kind: "user",
     actorType: "user",
@@ -3330,6 +3542,8 @@ const authenticateSessionToken = async (c: AppContext, token: string, touch: boo
     username: row.username,
     displayName: row.display_name,
     scopes: [],
+    workspaceId: workspace.workspaceId,
+    role: workspace.role,
     sessionId: row.id,
   };
 };
@@ -3369,6 +3583,15 @@ const getActorLabel = (c: AppContext) => {
   return auth?.actorId ? `${auth.actorType}:${auth.actorId}` : auth?.username ?? "user";
 };
 
+const getWorkspaceId = (c: AppContext) => c.get("auth").workspaceId;
+
+const requireOwner = (c: AppContext) => {
+  const auth = c.get("auth");
+  return auth?.kind === "user" && auth.role === "owner"
+    ? null
+    : forbidden(c, "Only the instance owner can manage users.");
+};
+
 const requireUser = (c: AppContext) => {
   const auth = c.get("auth");
 
@@ -3604,12 +3827,18 @@ const mapJsonBackupRevision = (row: BackupRevisionRow): JsonBackupRevision => ({
   createdAt: row.created_at,
 });
 
-const restoreJsonNotebooks = async (db: D1Database, notebooks: JsonBackupNotebook[]) => {
+const restoreJsonNotebooks = async (db: D1Database, workspaceId: string, notebooks: JsonBackupNotebook[]) => {
+  await assertIdsAvailableInWorkspace(db, "notebooks", workspaceId, notebooks.map((notebook) => notebook.id));
+  const importedIds = new Set(notebooks.map((notebook) => notebook.id));
+  const externalParentIds = notebooks
+    .map((notebook) => notebook.parentId)
+    .filter((id): id is string => Boolean(id) && !importedIds.has(id as string));
+  await assertNotebookIdsInWorkspace(db, workspaceId, externalParentIds);
   const statements = notebooks.map((notebook) =>
     db.prepare(
       `INSERT INTO notebooks (
-        id, parent_id, name, slug, icon, color, sort_order, is_deleted, created_at, updated_at, deleted_at
-      ) VALUES (?, ?, ?, ?, ?, ?, ?, 0, ?, ?, NULL)
+        id, workspace_id, parent_id, name, slug, icon, color, sort_order, is_deleted, created_at, updated_at, deleted_at
+      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, 0, ?, ?, NULL)
       ON CONFLICT(id) DO UPDATE SET
         parent_id = excluded.parent_id,
         name = excluded.name,
@@ -3622,6 +3851,7 @@ const restoreJsonNotebooks = async (db: D1Database, notebooks: JsonBackupNoteboo
         deleted_at = NULL`
     ).bind(
       notebook.id,
+      workspaceId,
       notebook.parentId,
       notebook.name,
       notebook.slug,
@@ -3636,7 +3866,9 @@ const restoreJsonNotebooks = async (db: D1Database, notebooks: JsonBackupNoteboo
   await db.batch(statements);
 };
 
-const restoreJsonMemos = async (db: D1Database, backups: JsonBackupMemo[]) => {
+const restoreJsonMemos = async (db: D1Database, workspaceId: string, backups: JsonBackupMemo[]) => {
+  await assertIdsAvailableInWorkspace(db, "memos", workspaceId, backups.map((backup) => backup.memo.id));
+  await assertNotebookIdsInWorkspace(db, workspaceId, backups.map((backup) => backup.memo.notebookId));
   for (const backup of backups) {
     const memo = backup.memo;
     const contentJson = parseDoc(JSON.stringify(memo.contentJson));
@@ -3653,10 +3885,10 @@ const restoreJsonMemos = async (db: D1Database, backups: JsonBackupMemo[]) => {
     await db.batch([
       db.prepare(
         `INSERT INTO memos (
-          id, notebook_id, title, excerpt, tags_json, is_pinned, is_archived, is_deleted,
+          id, workspace_id, notebook_id, title, excerpt, tags_json, is_pinned, is_archived, is_deleted,
           source_memo_ids, merge_source_count, merged_into_memo_id,
           created_by, updated_by, created_at, updated_at, deleted_at
-        ) VALUES (?, ?, ?, ?, ?, ?, ?, 0, ?, ?, NULL, 'restore', 'restore', ?, ?, NULL)
+        ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, 0, ?, ?, NULL, 'restore', 'restore', ?, ?, NULL)
         ON CONFLICT(id) DO UPDATE SET
           notebook_id = excluded.notebook_id,
           title = excluded.title,
@@ -3673,6 +3905,7 @@ const restoreJsonMemos = async (db: D1Database, backups: JsonBackupMemo[]) => {
           deleted_at = NULL`
       ).bind(
         memo.id,
+        workspaceId,
         memo.notebookId,
         title,
         createExcerpt(contentText),
@@ -3756,6 +3989,34 @@ const restoreJsonMemos = async (db: D1Database, backups: JsonBackupMemo[]) => {
   });
 };
 
+const assertIdsAvailableInWorkspace = async (
+  db: D1Database,
+  table: "notebooks" | "memos",
+  workspaceId: string,
+  ids: string[],
+) => {
+  if (ids.length === 0) return;
+  const placeholders = ids.map(() => "?").join(", ");
+  const collision = await db.prepare(
+    `SELECT id FROM ${table} WHERE workspace_id <> ? AND id IN (${placeholders}) LIMIT 1`
+  ).bind(workspaceId, ...ids).first<{ id: string }>();
+  if (collision) {
+    throw new AppError("cross_workspace_id_conflict", "Backup contains an ID already used by another user.", 409);
+  }
+};
+
+const assertNotebookIdsInWorkspace = async (db: D1Database, workspaceId: string, ids: string[]) => {
+  const uniqueIds = Array.from(new Set(ids));
+  if (uniqueIds.length === 0) return;
+  const placeholders = uniqueIds.map(() => "?").join(", ");
+  const rows = await db.prepare(
+    `SELECT id FROM notebooks WHERE workspace_id = ? AND id IN (${placeholders})`
+  ).bind(workspaceId, ...uniqueIds).all<{ id: string }>();
+  if (rows.results.length !== uniqueIds.length) {
+    throw new AppError("invalid_backup_workspace", "Backup references a notebook outside the current workspace.", 400);
+  }
+};
+
 const mapResource = (row: ResourceRow): Resource => ({
   id: row.id,
   memoId: row.memo_id,
@@ -3803,43 +4064,43 @@ const mapTagSummary = (row: TagSummaryRow): TagSummary => ({
   updatedAt: row.updated_at,
 });
 
-const getApiTokenRow = async (db: D1Database, id: string): Promise<ApiTokenRow | null> =>
+const getApiTokenRow = async (db: D1Database, id: string, workspaceId: string): Promise<ApiTokenRow | null> =>
   db
     .prepare(
-      `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at
+      `SELECT id, name, token_value, scopes_json, last_used_at, expires_at, is_revoked, created_at, workspace_id
        FROM api_tokens
-       WHERE id = ?`
+       WHERE id = ? AND workspace_id = ?`
     )
-    .bind(id)
+    .bind(id, workspaceId)
     .first<ApiTokenRow>();
 
-const listNotebooks = async (db: D1Database): Promise<Notebook[]> => {
+const listNotebooks = async (db: D1Database, workspaceId: string): Promise<Notebook[]> => {
   const rows = await db
     .prepare(
       notebookSelectSql(
-        `WHERE n.is_deleted = 0
+        `WHERE n.workspace_id = ? AND n.is_deleted = 0
          GROUP BY n.id, n.parent_id, n.name, n.slug, n.icon, n.color, n.sort_order, n.created_at, n.updated_at
          ORDER BY n.parent_id IS NOT NULL, n.sort_order ASC, n.name ASC`
       )
     )
-    .all<NotebookRow>();
+    .bind(workspaceId).all<NotebookRow>();
 
   return rows.results.map(mapNotebook);
 };
 
-const listTagSummaries = async (db: D1Database): Promise<TagSummary[]> => {
+const listTagSummaries = async (db: D1Database, workspaceId: string): Promise<TagSummary[]> => {
   const rows = await db
     .prepare(
       `SELECT json_each.value AS name,
               COUNT(DISTINCT m.id) AS memo_count,
               MAX(m.updated_at) AS updated_at
        FROM memos m, json_each(m.tags_json)
-       WHERE m.is_deleted = 0
+       WHERE m.workspace_id = ? AND m.is_deleted = 0
          AND trim(json_each.value) <> ''
        GROUP BY json_each.value
        ORDER BY lower(json_each.value) ASC`
     )
-    .all<TagSummaryRow>();
+    .bind(workspaceId).all<TagSummaryRow>();
 
   return rows.results
     .filter((row) => typeof row.name === "string" && row.name.trim())
@@ -3848,6 +4109,7 @@ const listTagSummaries = async (db: D1Database): Promise<TagSummary[]> => {
 
 const updateTagAcrossMemos = async (
   db: D1Database,
+  workspaceId: string,
   oldTag: string,
   nextTag: string | null,
   actor: { actorType: "user" | "agent"; actorId: string | null },
@@ -3865,14 +4127,14 @@ const updateTagAcrossMemos = async (
       `SELECT m.id, m.title, m.tags_json, c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = 0
+       WHERE m.workspace_id = ? AND m.is_deleted = 0
          AND EXISTS (
            SELECT 1
            FROM json_each(m.tags_json)
            WHERE json_each.value = ?
          )`
     )
-    .bind(normalizedOld)
+    .bind(workspaceId, normalizedOld)
     .all<MemoTagUpdateRow>();
 
   const now = isoNow();
@@ -3901,9 +4163,9 @@ const updateTagAcrossMemos = async (
         .prepare(
           `UPDATE memos
            SET tags_json = ?, updated_by = ?, updated_at = ?
-           WHERE id = ? AND is_deleted = 0`
+           WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
         )
-        .bind(JSON.stringify(nextTags), actorLabel, now, row.id),
+        .bind(JSON.stringify(nextTags), actorLabel, now, row.id, workspaceId),
       db.prepare(`DELETE FROM memos_fts WHERE memo_id = ?`).bind(row.id),
       db
         .prepare(
@@ -3926,7 +4188,7 @@ const updateTagAcrossMemos = async (
   return updated;
 };
 
-const previewTagRename = async (db: D1Database, oldTag: string, nextTag: string | null) => {
+const previewTagRename = async (db: D1Database, workspaceId: string, oldTag: string, nextTag: string | null) => {
   const normalizedOld = normalizeTags([oldTag])[0];
   const normalizedNext = nextTag === null ? null : normalizeTags([nextTag])[0];
 
@@ -3934,7 +4196,7 @@ const previewTagRename = async (db: D1Database, oldTag: string, nextTag: string
     return { dryRun: true, updated: 0, changes: [] };
   }
 
-  const rows = await getMemoRowsByTag(db, normalizedOld);
+  const rows = await getMemoRowsByTag(db, workspaceId, normalizedOld);
   const changes = rows.map((row) => {
     const currentTags = parseJsonArray(row.tags_json);
     const nextTags = normalizeTags(
@@ -3958,20 +4220,20 @@ const previewTagRename = async (db: D1Database, oldTag: string, nextTag: string
   return { dryRun: true, updated: changes.length, changes };
 };
 
-const getMemoRowsByTag = async (db: D1Database, tag: string) => {
+const getMemoRowsByTag = async (db: D1Database, workspaceId: string, tag: string) => {
   const rows = await db
     .prepare(
       `SELECT m.id, m.title, m.tags_json, c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = 0
+       WHERE m.workspace_id = ? AND m.is_deleted = 0
          AND EXISTS (
            SELECT 1
            FROM json_each(m.tags_json)
            WHERE json_each.value = ?
          )`
     )
-    .bind(tag)
+    .bind(workspaceId, tag)
     .all<MemoTagUpdateRow>();
 
   return rows.results;
@@ -3980,6 +4242,7 @@ const getMemoRowsByTag = async (db: D1Database, tag: string) => {
 const updateTagsForMemos = async (
   db: D1Database,
   input: {
+    workspaceId: string;
     memoIds: string[];
     tags: string[];
     mode: "add" | "remove";
@@ -4001,9 +4264,9 @@ const updateTagsForMemos = async (
       `SELECT m.id, m.title, m.tags_json, c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = 0 AND m.id IN (${placeholders})`
+       WHERE m.workspace_id = ? AND m.is_deleted = 0 AND m.id IN (${placeholders})`
     )
-    .bind(...memoIds)
+    .bind(input.workspaceId, ...memoIds)
     .all<MemoTagUpdateRow>();
 
   if (rows.results.length !== memoIds.length) {
@@ -4049,9 +4312,9 @@ const updateTagsForMemos = async (
         .prepare(
           `UPDATE memos
            SET tags_json = ?, updated_by = ?, updated_at = ?
-           WHERE id = ? AND is_deleted = 0`
+           WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
         )
-        .bind(JSON.stringify(change.nextTags), input.actorLabel, now, change.memoId),
+        .bind(JSON.stringify(change.nextTags), input.actorLabel, now, change.memoId, input.workspaceId),
       db.prepare(`DELETE FROM memos_fts WHERE memo_id = ?`).bind(change.memoId),
       db
         .prepare(
@@ -4072,6 +4335,7 @@ const updateTagsForMemos = async (
 const searchMemoSummaries = async (
   db: D1Database,
   options: {
+    workspaceId: string;
     query?: string | null;
     notebookId?: string | null;
     tags?: string[];
@@ -4088,8 +4352,8 @@ const searchMemoSummaries = async (
   const notebookId = options.notebookId?.trim() || null;
   const tags = normalizeTags(options.tags ?? []);
   const limit = clampNumber(options.limit, 1, 100);
-  const filters = ["m.is_deleted = 0"];
-  const binds: unknown[] = [];
+  const filters = ["m.workspace_id = ?", "m.is_deleted = 0"];
+  const binds: unknown[] = [options.workspaceId];
 
   if (notebookId) {
     filters.push("m.notebook_id = ?");
@@ -4196,7 +4460,7 @@ const searchMemoSummaries = async (
 
 const listMemosForMcp = async (
   db: D1Database,
-  options: { notebookId?: string | null; limit: number; offset: number; includeContent: boolean; includeDeleted: boolean }
+  options: { workspaceId: string; notebookId?: string | null; limit: number; offset: number; includeContent: boolean; includeDeleted: boolean }
 ) => {
   const notebookId = options.notebookId?.trim() || null;
   const limit = clampNumber(options.limit, 1, 100);
@@ -4213,12 +4477,12 @@ const listMemosForMcp = async (
                 m.source_memo_ids, m.merge_source_count, m.merged_into_memo_id
          FROM memos m
          INNER JOIN memo_contents c ON c.memo_id = m.id
-         WHERE ${deletedFilter}
+         WHERE m.workspace_id = ? AND ${deletedFilter}
            AND (? IS NULL OR m.notebook_id = ?)
          ORDER BY m.updated_at DESC, m.id ASC
          LIMIT ? OFFSET ?`
       )
-      .bind(notebookId, notebookId, pageSize, offset)
+      .bind(options.workspaceId, notebookId, notebookId, pageSize, offset)
       .all<MemoDetailRow>();
     const page = rows.results.slice(0, limit).map(mapMemoDetail);
 
@@ -4238,12 +4502,12 @@ const listMemosForMcp = async (
               c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE ${deletedFilter}
+       WHERE m.workspace_id = ? AND ${deletedFilter}
          AND (? IS NULL OR m.notebook_id = ?)
        ORDER BY m.updated_at DESC, m.id ASC
        LIMIT ? OFFSET ?`
     )
-    .bind(notebookId, notebookId, pageSize, offset)
+    .bind(options.workspaceId, notebookId, notebookId, pageSize, offset)
     .all<MemoSummaryRow>();
   const page = rows.results.slice(0, limit).map(mapMemoSummary);
 
@@ -4256,15 +4520,15 @@ const listMemosForMcp = async (
   };
 };
 
-const getNotebook = async (db: D1Database, id: string): Promise<Notebook | null> => {
+const getNotebook = async (db: D1Database, workspaceId: string, id: string): Promise<Notebook | null> => {
   const row = await db
     .prepare(
       notebookSelectSql(
-        `WHERE n.id = ? AND n.is_deleted = 0
+        `WHERE n.id = ? AND n.workspace_id = ? AND n.is_deleted = 0
          GROUP BY n.id, n.parent_id, n.name, n.slug, n.icon, n.color, n.sort_order, n.created_at, n.updated_at`
       )
     )
-    .bind(id)
+    .bind(id, workspaceId)
     .first<NotebookRow>();
 
   return row ? mapNotebook(row) : null;
@@ -4272,12 +4536,13 @@ const getNotebook = async (db: D1Database, id: string): Promise<Notebook | null>
 
 const createNotebookRecord = async (
   db: D1Database,
+  workspaceId: string,
   input: NotebookCreateInput & { sortOrder?: number },
   actor: { actorType: "user" | "agent"; actorId: string | null }
 ) => {
   const parentId = input.parentId ?? null;
 
-  if (parentId && !(await getNotebook(db, parentId))) {
+  if (parentId && !(await getNotebook(db, workspaceId, parentId))) {
     throw new AppError("not_found", "Parent notebook not found", 404);
   }
 
@@ -4288,10 +4553,10 @@ const createNotebookRecord = async (
   await db.batch([
     db
       .prepare(
-        `INSERT INTO notebooks (id, parent_id, name, slug, sort_order, created_at, updated_at)
-         VALUES (?, ?, ?, ?, ?, ?, ?)`
+        `INSERT INTO notebooks (id, workspace_id, parent_id, name, slug, sort_order, created_at, updated_at)
+         VALUES (?, ?, ?, ?, ?, ?, ?, ?)`
       )
-      .bind(id, parentId, input.name, slugify(input.name), sortOrder, now, now),
+      .bind(id, workspaceId, parentId, input.name, slugify(input.name), sortOrder, now, now),
     auditStatement(db, actor.actorType, actor.actorId, "notebook.create", "notebook", id, {
       name: input.name,
       parentId,
@@ -4299,7 +4564,7 @@ const createNotebookRecord = async (
     }),
   ]);
 
-  const notebook = await getNotebook(db, id);
+  const notebook = await getNotebook(db, workspaceId, id);
 
   if (!notebook) {
     throw new AppError("not_found", "Notebook not found after create", 404);
@@ -4310,11 +4575,12 @@ const createNotebookRecord = async (
 
 const updateNotebookRecord = async (
   db: D1Database,
+  workspaceId: string,
   id: string,
   input: { name?: string; parentId?: string | null; sortOrder?: number },
   actor: { actorType: "user" | "agent"; actorId: string | null }
 ) => {
-  const current = await getNotebook(db, id);
+  const current = await getNotebook(db, workspaceId, id);
 
   if (!current) {
     throw new AppError("not_found", "Notebook not found", 404);
@@ -4330,13 +4596,13 @@ const updateNotebookRecord = async (
   }
 
   if (nextParentId) {
-    const parent = await getNotebook(db, nextParentId);
+    const parent = await getNotebook(db, workspaceId, nextParentId);
 
     if (!parent) {
       throw new AppError("not_found", "Parent notebook not found", 404);
     }
 
-    if (await isNotebookDescendant(db, nextParentId, id)) {
+    if (await isNotebookDescendant(db, workspaceId, nextParentId, id)) {
       throw new AppError("notebook_cycle", "Notebook cannot be moved into its own descendant.", 409);
     }
   }
@@ -4346,13 +4612,13 @@ const updateNotebookRecord = async (
       .prepare(
         `UPDATE notebooks
          SET name = ?, slug = ?, parent_id = ?, sort_order = ?, updated_at = ?
-         WHERE id = ? AND is_deleted = 0`
+         WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
       )
-      .bind(nextName, slugify(nextName), nextParentId ?? null, nextSortOrder, now, id),
+      .bind(nextName, slugify(nextName), nextParentId ?? null, nextSortOrder, now, id, workspaceId),
     auditStatement(db, actor.actorType, actor.actorId, "notebook.update", "notebook", id, input),
   ]);
 
-  const notebook = await getNotebook(db, id);
+  const notebook = await getNotebook(db, workspaceId, id);
 
   if (!notebook) {
     throw new AppError("not_found", "Notebook not found after update", 404);
@@ -4361,27 +4627,27 @@ const updateNotebookRecord = async (
   return notebook;
 };
 
-const isNotebookDescendant = async (db: D1Database, candidateId: string, ancestorId: string) => {
+const isNotebookDescendant = async (db: D1Database, workspaceId: string, candidateId: string, ancestorId: string) => {
   const row = await db
     .prepare(
       `WITH RECURSIVE descendants(id) AS (
          SELECT id
          FROM notebooks
-         WHERE parent_id = ? AND is_deleted = 0
+         WHERE workspace_id = ? AND parent_id = ? AND is_deleted = 0
 
          UNION ALL
 
          SELECT n.id
          FROM notebooks n
          INNER JOIN descendants d ON n.parent_id = d.id
-         WHERE n.is_deleted = 0
+         WHERE n.workspace_id = ? AND n.is_deleted = 0
        )
        SELECT id
        FROM descendants
        WHERE id = ?
        LIMIT 1`
     )
-    .bind(ancestorId, candidateId)
+    .bind(workspaceId, ancestorId, workspaceId, candidateId)
     .first<{ id: string }>();
 
   return Boolean(row);
@@ -4389,6 +4655,7 @@ const isNotebookDescendant = async (db: D1Database, candidateId: string, ancesto
 
 const getMemoDetailRow = async (
   db: D1Database,
+  workspaceId: string,
   id: string,
   includeDeleted = false
 ): Promise<MemoDetailRow | null> =>
@@ -4400,19 +4667,20 @@ const getMemoDetailRow = async (
               m.source_memo_ids, m.merge_source_count, m.merged_into_memo_id
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.id = ? AND (? = 1 OR m.is_deleted = 0)`
+       WHERE m.id = ? AND m.workspace_id = ? AND (? = 1 OR m.is_deleted = 0)`
     )
-    .bind(id, includeDeleted ? 1 : 0)
+    .bind(id, workspaceId, includeDeleted ? 1 : 0)
     .first<MemoDetailRow>();
 
-const getMemoDetail = async (db: D1Database, id: string, includeDeleted = false): Promise<MemoDetail | null> => {
-  const row = await getMemoDetailRow(db, id, includeDeleted);
+const getMemoDetail = async (db: D1Database, workspaceId: string, id: string, includeDeleted = false): Promise<MemoDetail | null> => {
+  const row = await getMemoDetailRow(db, workspaceId, id, includeDeleted);
   return row ? mapMemoDetail(row) : null;
 };
 
 const deleteMemosRecord = async (
   db: D1Database,
   resourcesBucket: R2Bucket,
+  workspaceId: string,
   memoIds: string[],
   permanent: boolean,
   actor: { actorType: "user" | "agent"; actorId: string | null }
@@ -4429,9 +4697,9 @@ const deleteMemosRecord = async (
     .prepare(
       `SELECT id
        FROM memos
-       WHERE is_deleted = ? AND id IN (${placeholders})`
+       WHERE workspace_id = ? AND is_deleted = ? AND id IN (${placeholders})`
     )
-    .bind(expectedDeletedState, ...uniqueMemoIds)
+    .bind(workspaceId, expectedDeletedState, ...uniqueMemoIds)
     .all<{ id: string }>();
 
   if (rows.results.length !== uniqueMemoIds.length) {
@@ -4465,7 +4733,7 @@ const deleteMemosRecord = async (
       db.prepare(`DELETE FROM resources WHERE memo_id IN (${placeholders})`).bind(...uniqueMemoIds),
       db.prepare(`DELETE FROM memo_revisions WHERE memo_id IN (${placeholders})`).bind(...uniqueMemoIds),
       db.prepare(`DELETE FROM memo_contents WHERE memo_id IN (${placeholders})`).bind(...uniqueMemoIds),
-      db.prepare(`DELETE FROM memos WHERE is_deleted = 1 AND id IN (${placeholders})`).bind(...uniqueMemoIds)
+      db.prepare(`DELETE FROM memos WHERE workspace_id = ? AND is_deleted = 1 AND id IN (${placeholders})`).bind(workspaceId, ...uniqueMemoIds)
     );
 
     for (const memoId of uniqueMemoIds) {
@@ -4477,9 +4745,9 @@ const deleteMemosRecord = async (
         .prepare(
           `UPDATE memos
            SET is_deleted = 1, deleted_at = ?, updated_at = ?
-           WHERE is_deleted = 0 AND id IN (${placeholders})`
+           WHERE workspace_id = ? AND is_deleted = 0 AND id IN (${placeholders})`
         )
-        .bind(now, now, ...uniqueMemoIds),
+        .bind(now, now, workspaceId, ...uniqueMemoIds),
       db
         .prepare(
           `UPDATE resources
@@ -4499,7 +4767,7 @@ const deleteMemosRecord = async (
   return uniqueMemoIds.length;
 };
 
-const getMemosForBulkAction = async (db: D1Database, memoIds: string[], deletedState: 0 | 1) => {
+const getMemosForBulkAction = async (db: D1Database, workspaceId: string, memoIds: string[], deletedState: 0 | 1) => {
   const uniqueMemoIds = Array.from(new Set(memoIds));
 
   if (uniqueMemoIds.length === 0) {
@@ -4514,11 +4782,11 @@ const getMemosForBulkAction = async (db: D1Database, memoIds: string[], deletedS
               c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = ?
+       WHERE m.workspace_id = ? AND m.is_deleted = ?
          AND m.id IN (${placeholders})
        ORDER BY m.updated_at DESC, m.id ASC`
     )
-    .bind(deletedState, ...uniqueMemoIds)
+    .bind(workspaceId, deletedState, ...uniqueMemoIds)
     .all<MemoSummaryRow>();
 
   if (rows.results.length !== uniqueMemoIds.length) {
@@ -4530,6 +4798,7 @@ const getMemosForBulkAction = async (db: D1Database, memoIds: string[], deletedS
 
 const restoreMemosRecord = async (
   db: D1Database,
+  workspaceId: string,
   memoIds: string[],
   actor: { actorType: "user" | "agent"; actorId: string | null }
 ) => {
@@ -4545,9 +4814,9 @@ const restoreMemosRecord = async (
       `SELECT m.id, m.notebook_id, m.title, m.tags_json, c.content_text
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = 1 AND m.id IN (${placeholders})`
+       WHERE m.workspace_id = ? AND m.is_deleted = 1 AND m.id IN (${placeholders})`
     )
-    .bind(...uniqueMemoIds)
+    .bind(workspaceId, ...uniqueMemoIds)
     .all<{ id: string; notebook_id: string; title: string | null; tags_json: string; content_text: string }>();
 
   if (rows.results.length !== uniqueMemoIds.length) {
@@ -4557,14 +4826,17 @@ const restoreMemosRecord = async (
   const notebookIds = Array.from(new Set(rows.results.map((row) => row.notebook_id)));
   const notebookPlaceholders = notebookIds.map(() => "?").join(", ");
   const notebookRows = await db
-    .prepare(`SELECT id FROM notebooks WHERE is_deleted = 0 AND id IN (${notebookPlaceholders})`)
-    .bind(...notebookIds)
+    .prepare(`SELECT id FROM notebooks WHERE workspace_id = ? AND is_deleted = 0 AND id IN (${notebookPlaceholders})`)
+    .bind(workspaceId, ...notebookIds)
     .all<{ id: string }>();
   const activeNotebookIds = new Set(notebookRows.results.map((row) => row.id));
 
   const needsInbox = rows.results.some((row) => !activeNotebookIds.has(row.notebook_id));
 
-  if (needsInbox && !(await getNotebook(db, "nb_inbox"))) {
+  const inbox = needsInbox
+    ? await db.prepare(`SELECT id FROM notebooks WHERE workspace_id = ? AND slug = 'inbox' AND is_deleted = 0 LIMIT 1`).bind(workspaceId).first<{ id: string }>()
+    : null;
+  if (needsInbox && !inbox) {
     throw new AppError("restore_notebook_missing", "Original notebooks were deleted and the default inbox is unavailable.", 409);
   }
 
@@ -4572,7 +4844,7 @@ const restoreMemosRecord = async (
   const statements: D1PreparedStatement[] = [];
 
   for (const row of rows.results) {
-    const restoreNotebookId = activeNotebookIds.has(row.notebook_id) ? row.notebook_id : "nb_inbox";
+    const restoreNotebookId = activeNotebookIds.has(row.notebook_id) ? row.notebook_id : inbox!.id;
     const tags = parseJsonArray(row.tags_json);
 
     statements.push(
@@ -4580,9 +4852,9 @@ const restoreMemosRecord = async (
         .prepare(
           `UPDATE memos
            SET notebook_id = ?, is_deleted = 0, deleted_at = NULL, updated_at = ?
-           WHERE id = ? AND is_deleted = 1`
+           WHERE id = ? AND workspace_id = ? AND is_deleted = 1`
         )
-        .bind(restoreNotebookId, now, row.id),
+        .bind(restoreNotebookId, now, row.id, workspaceId),
       db
         .prepare(
           `UPDATE resources
@@ -4611,15 +4883,16 @@ const restoreMemosRecord = async (
 const emptyTrashMemosRecord = async (
   db: D1Database,
   resourcesBucket: R2Bucket,
+  workspaceId: string,
   actor: { actorType: "user" | "agent"; actorId: string | null }
 ) => {
   const countRow = await db
     .prepare(
       `SELECT COUNT(*) AS count
        FROM memos
-       WHERE is_deleted = 1`
+       WHERE workspace_id = ? AND is_deleted = 1`
     )
-    .first<{ count: number }>();
+    .bind(workspaceId).first<{ count: number }>();
   const deleted = countRow?.count ?? 0;
 
   if (deleted === 0) {
@@ -4631,9 +4904,9 @@ const emptyTrashMemosRecord = async (
       `SELECT r.object_key
        FROM resources r
        INNER JOIN memos m ON m.id = r.memo_id
-       WHERE m.is_deleted = 1`
+       WHERE m.workspace_id = ? AND m.is_deleted = 1`
     )
-    .all<{ object_key: string }>();
+    .bind(workspaceId).all<{ object_key: string }>();
   const objectKeys = resourceRows.results.map((resource) => resource.object_key);
 
   if (objectKeys.length > 0) {
@@ -4641,12 +4914,12 @@ const emptyTrashMemosRecord = async (
   }
 
   await db.batch([
-    db.prepare(`DELETE FROM memos_fts WHERE memo_id IN (SELECT id FROM memos WHERE is_deleted = 1)`),
-    db.prepare(`UPDATE resources SET original_memo_id = NULL WHERE original_memo_id IN (SELECT id FROM memos WHERE is_deleted = 1)`),
-    db.prepare(`DELETE FROM resources WHERE memo_id IN (SELECT id FROM memos WHERE is_deleted = 1)`),
-    db.prepare(`DELETE FROM memo_revisions WHERE memo_id IN (SELECT id FROM memos WHERE is_deleted = 1)`),
-    db.prepare(`DELETE FROM memo_contents WHERE memo_id IN (SELECT id FROM memos WHERE is_deleted = 1)`),
-    db.prepare(`DELETE FROM memos WHERE is_deleted = 1`),
+    db.prepare(`DELETE FROM memos_fts WHERE memo_id IN (SELECT id FROM memos WHERE workspace_id = ? AND is_deleted = 1)`).bind(workspaceId),
+    db.prepare(`UPDATE resources SET original_memo_id = NULL WHERE original_memo_id IN (SELECT id FROM memos WHERE workspace_id = ? AND is_deleted = 1)`).bind(workspaceId),
+    db.prepare(`DELETE FROM resources WHERE memo_id IN (SELECT id FROM memos WHERE workspace_id = ? AND is_deleted = 1)`).bind(workspaceId),
+    db.prepare(`DELETE FROM memo_revisions WHERE memo_id IN (SELECT id FROM memos WHERE workspace_id = ? AND is_deleted = 1)`).bind(workspaceId),
+    db.prepare(`DELETE FROM memo_contents WHERE memo_id IN (SELECT id FROM memos WHERE workspace_id = ? AND is_deleted = 1)`).bind(workspaceId),
+    db.prepare(`DELETE FROM memos WHERE workspace_id = ? AND is_deleted = 1`).bind(workspaceId),
     auditStatement(db, actor.actorType, actor.actorId, "memo.trash_empty", "trash", "memos", { deleted }),
   ]);
 
@@ -4884,6 +5157,7 @@ const resetDemoData = async (env: Bindings, scheduledTime: number) => {
 
 const moveMemosToNotebook = async (
   db: D1Database,
+  workspaceId: string,
   memoIds: string[],
   notebookId: string,
   actor: { actorType: "user" | "agent"; actorId: string | null },
@@ -4900,9 +5174,9 @@ const moveMemosToNotebook = async (
     .prepare(
       `SELECT id, notebook_id
        FROM memos
-       WHERE is_deleted = 0 AND id IN (${placeholders})`
+       WHERE workspace_id = ? AND is_deleted = 0 AND id IN (${placeholders})`
     )
-    .bind(...uniqueMemoIds)
+    .bind(workspaceId, ...uniqueMemoIds)
     .all<{ id: string; notebook_id: string }>();
 
   if (rows.results.length !== uniqueMemoIds.length) {
@@ -4915,9 +5189,9 @@ const moveMemosToNotebook = async (
       .prepare(
         `UPDATE memos
          SET notebook_id = ?, updated_by = ?, updated_at = ?
-         WHERE is_deleted = 0 AND id IN (${placeholders})`
+         WHERE workspace_id = ? AND is_deleted = 0 AND id IN (${placeholders})`
       )
-      .bind(notebookId, actorLabel, now, ...uniqueMemoIds),
+      .bind(notebookId, actorLabel, now, workspaceId, ...uniqueMemoIds),
   ];
 
   for (const row of rows.results) {
@@ -4935,6 +5209,7 @@ const moveMemosToNotebook = async (
 
 const mergeMemosRecord = async (
   db: D1Database,
+  workspaceId: string,
   input: { memoIds: string[]; notebookId?: string; title?: string },
   actor: { actorType: "user" | "agent"; actorId: string | null },
   actorLabel: string
@@ -4954,16 +5229,16 @@ const mergeMemosRecord = async (
               m.source_memo_ids, m.merge_source_count, m.merged_into_memo_id
        FROM memos m
        INNER JOIN memo_contents c ON c.memo_id = m.id
-       WHERE m.is_deleted = 0 AND m.id IN (${placeholders})`
+       WHERE m.workspace_id = ? AND m.is_deleted = 0 AND m.id IN (${placeholders})`
     )
-    .bind(...uniqueMemoIds)
+    .bind(workspaceId, ...uniqueMemoIds)
     .all<MemoDetailRow>();
 
   if (rows.results.length !== uniqueMemoIds.length) {
     throw new AppError("missing_memos", "One or more memos cannot be merged.", 400);
   }
 
-  if (input.notebookId && !(await getNotebook(db, input.notebookId))) {
+  if (input.notebookId && !(await getNotebook(db, workspaceId, input.notebookId))) {
     throw new AppError("not_found", "Target notebook not found", 404);
   }
 
@@ -4985,12 +5260,13 @@ const mergeMemosRecord = async (
     db
       .prepare(
         `INSERT INTO memos (
-          id, notebook_id, title, excerpt, tags_json, source_memo_ids, merge_source_count,
+          id, workspace_id, notebook_id, title, excerpt, tags_json, source_memo_ids, merge_source_count,
           created_by, updated_by, created_at, updated_at
-        ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
+        ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)`
       )
       .bind(
         newMemoId,
+        workspaceId,
         notebookId,
         title,
         excerpt,
@@ -5019,9 +5295,9 @@ const mergeMemosRecord = async (
       .prepare(
         `UPDATE memos
          SET is_deleted = 1, deleted_at = ?, merged_into_memo_id = ?, merged_at = ?, updated_at = ?
-         WHERE id IN (${placeholders})`
+         WHERE workspace_id = ? AND id IN (${placeholders})`
       )
-      .bind(now, newMemoId, now, now, ...uniqueMemoIds),
+      .bind(now, newMemoId, now, now, workspaceId, ...uniqueMemoIds),
     db.prepare(`DELETE FROM memos_fts WHERE memo_id IN (${placeholders})`).bind(...uniqueMemoIds),
     db
       .prepare(
@@ -5037,7 +5313,7 @@ const mergeMemosRecord = async (
     }),
   ]);
 
-  const memo = await getMemoDetail(db, newMemoId);
+  const memo = await getMemoDetail(db, workspaceId, newMemoId);
 
   if (!memo) {
     throw new AppError("not_found", "Merged memo not found after create.", 404);
@@ -5048,6 +5324,7 @@ const mergeMemosRecord = async (
 
 const createMemoRecord = async (
   db: D1Database,
+  workspaceId: string,
   input: { notebookId: string; title?: string; contentMarkdown?: string; tags?: string[]; createdAt?: string; updatedAt?: string },
   actor: { actorType: "user" | "agent"; actorId: string | null },
   actorLabel: string
@@ -5068,10 +5345,10 @@ const createMemoRecord = async (
     db
       .prepare(
         `INSERT INTO memos (
-          id, notebook_id, title, excerpt, tags_json, created_by, updated_by, created_at, updated_at
-        ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?)`
+          id, workspace_id, notebook_id, title, excerpt, tags_json, created_by, updated_by, created_at, updated_at
+        ) SELECT ?, ?, id, ?, ?, ?, ?, ?, ?, ? FROM notebooks WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
       )
-      .bind(id, input.notebookId, title, excerpt, JSON.stringify(tags), actorLabel, actorLabel, createdAt, updatedAt),
+      .bind(id, workspaceId, title, excerpt, JSON.stringify(tags), actorLabel, actorLabel, createdAt, updatedAt, input.notebookId, workspaceId),
     db
       .prepare(
         `INSERT INTO memo_contents (
@@ -5090,7 +5367,7 @@ const createMemoRecord = async (
     }),
   ]);
 
-  const memo = await getMemoDetail(db, id);
+  const memo = await getMemoDetail(db, workspaceId, id);
 
   if (!memo) {
     throw new Error("Memo was created but could not be read.");
@@ -5101,6 +5378,7 @@ const createMemoRecord = async (
 
 const updateMemoRecord = async (
   db: D1Database,
+  workspaceId: string,
   id: string,
   input: {
     expectedRevision?: number;
@@ -5117,7 +5395,7 @@ const updateMemoRecord = async (
   actor: { actorType: "user" | "agent"; actorId: string | null },
   actorLabel: string
 ): Promise<{ memo: MemoDetail; error?: never; message?: never } | { error: string; message: string }> => {
-  const current = await getMemoDetailRow(db, id);
+  const current = await getMemoDetailRow(db, workspaceId, id);
 
   if (!current) {
     return { error: "not_found", message: "Memo not found" };
@@ -5141,7 +5419,7 @@ const updateMemoRecord = async (
 
   if (!hasContentUpdate) {
     if (input.isPinned === undefined || isPinned === Boolean(current.is_pinned)) {
-      const memo = await getMemoDetail(db, id);
+      const memo = await getMemoDetail(db, workspaceId, id);
 
       if (!memo) {
         return { error: "not_found", message: "Memo not found after update" };
@@ -5155,13 +5433,13 @@ const updateMemoRecord = async (
         .prepare(
           `UPDATE memos
            SET is_pinned = ?, updated_by = ?, updated_at = ?, created_at = COALESCE(?, created_at)
-           WHERE id = ? AND is_deleted = 0`
+           WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
         )
-        .bind(isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id),
+        .bind(isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id, workspaceId),
       auditStatement(db, actor.actorType, actor.actorId, isPinned ? "memo.pin" : "memo.unpin", "memo", id, {}),
     ]);
 
-    const memo = await getMemoDetail(db, id);
+    const memo = await getMemoDetail(db, workspaceId, id);
 
     if (!memo) {
       return { error: "not_found", message: "Memo not found after update" };
@@ -5206,9 +5484,10 @@ const updateMemoRecord = async (
       .prepare(
         `UPDATE memos
          SET notebook_id = ?, title = ?, excerpt = ?, tags_json = ?, is_pinned = ?, updated_by = ?, updated_at = ?, created_at = COALESCE(?, created_at)
-         WHERE id = ? AND is_deleted = 0`
+         WHERE id = ? AND workspace_id = ? AND is_deleted = 0
+           AND EXISTS (SELECT 1 FROM notebooks n WHERE n.id = ? AND n.workspace_id = ? AND n.is_deleted = 0)`
       )
-      .bind(notebookId, title, excerpt, JSON.stringify(tags), isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id),
+      .bind(notebookId, title, excerpt, JSON.stringify(tags), isPinned ? 1 : 0, actorLabel, updatedAt, input.createdAt ?? null, id, workspaceId, notebookId, workspaceId),
     db
       .prepare(
         `UPDATE memo_contents
@@ -5229,7 +5508,7 @@ const updateMemoRecord = async (
     }),
   ]);
 
-  const memo = await getMemoDetail(db, id);
+  const memo = await getMemoDetail(db, workspaceId, id);
 
   if (!memo) {
     return { error: "not_found", message: "Memo not found after update" };
@@ -5240,21 +5519,23 @@ const updateMemoRecord = async (
 
 const getMemoRevisionRow = async (
   db: D1Database,
+  workspaceId: string,
   memoId: string,
   revisionId: string
 ): Promise<MemoRevisionRow | null> =>
   db
     .prepare(
-      `SELECT id, memo_id, revision, title, tags_json, content_json, content_markdown,
-              content_text, content_hash, created_by, created_at
-       FROM memo_revisions
-       WHERE id = ? AND memo_id = ?`
+      `SELECT mr.id, mr.memo_id, mr.revision, mr.title, mr.tags_json, mr.content_json, mr.content_markdown,
+              mr.content_text, mr.content_hash, mr.created_by, mr.created_at
+       FROM memo_revisions mr
+       INNER JOIN memos m ON m.id = mr.memo_id
+       WHERE mr.id = ? AND mr.memo_id = ? AND m.workspace_id = ?`
     )
-    .bind(revisionId, memoId)
+    .bind(revisionId, memoId, workspaceId)
     .first<MemoRevisionRow>();
 
-const listMemoRevisions = async (db: D1Database, memoId: string, limit: number): Promise<MemoRevision[]> => {
-  const memo = await getMemoDetail(db, memoId, true);
+const listMemoRevisions = async (db: D1Database, workspaceId: string, memoId: string, limit: number): Promise<MemoRevision[]> => {
+  const memo = await getMemoDetail(db, workspaceId, memoId, true);
 
   if (!memo) {
     throw new AppError("not_found", "Memo not found", 404);
@@ -5277,18 +5558,19 @@ const listMemoRevisions = async (db: D1Database, memoId: string, limit: number):
 
 const restoreMemoRevisionRecord = async (
   db: D1Database,
+  workspaceId: string,
   memoId: string,
   revisionId: string,
   actor: { actorType: "user" | "agent"; actorId: string | null },
   actorLabel: string
 ) => {
-  const current = await getMemoDetailRow(db, memoId);
+  const current = await getMemoDetailRow(db, workspaceId, memoId);
 
   if (!current) {
     throw new AppError("not_found", "Memo not found", 404);
   }
 
-  const revision = await getMemoRevisionRow(db, memoId, revisionId);
+  const revision = await getMemoRevisionRow(db, workspaceId, memoId, revisionId);
 
   if (!revision) {
     throw new AppError("not_found", "Memo revision not found", 404);
@@ -5310,9 +5592,9 @@ const restoreMemoRevisionRecord = async (
       .prepare(
         `UPDATE memos
          SET title = ?, excerpt = ?, tags_json = ?, updated_by = ?, updated_at = ?
-         WHERE id = ? AND is_deleted = 0`
+         WHERE id = ? AND workspace_id = ? AND is_deleted = 0`
       )
-      .bind(title, excerpt, JSON.stringify(tags), actorLabel, now, memoId),
+      .bind(title, excerpt, JSON.stringify(tags), actorLabel, now, memoId, workspaceId),
     db
       .prepare(
         `UPDATE memo_contents
@@ -5335,7 +5617,7 @@ const restoreMemoRevisionRecord = async (
     }),
   ]);
 
-  const memo = await getMemoDetail(db, memoId);
+  const memo = await getMemoDetail(db, workspaceId, memoId);
 
   if (!memo) {
     throw new AppError("not_found", "Memo not found after revision restore", 404);
@@ -5419,47 +5701,50 @@ const shouldSnapshotMemoRevision = async (
   return Date.parse(now) - Date.parse(latest.created_at) >= REVISION_SNAPSHOT_INTERVAL_MS;
 };
 
-const getResourceRow = async (db: D1Database, id: string): Promise<ResourceRow | null> =>
+const getResourceRow = async (db: D1Database, workspaceId: string, id: string): Promise<ResourceRow | null> =>
   db
     .prepare(
-      `SELECT id, memo_id, original_memo_id, bucket_name, object_key, kind, mime_type,
-              filename, byte_size, sha256, width, height, created_at, updated_at
-       FROM resources
-       WHERE id = ? AND is_deleted = 0`
+      `SELECT r.id, r.memo_id, r.original_memo_id, r.bucket_name, r.object_key, r.kind, r.mime_type,
+              r.filename, r.byte_size, r.sha256, r.width, r.height, r.created_at, r.updated_at
+       FROM resources r
+       INNER JOIN memos m ON m.id = r.memo_id
+       WHERE r.id = ? AND m.workspace_id = ? AND r.is_deleted = 0`
     )
-    .bind(id)
+    .bind(id, workspaceId)
     .first<ResourceRow>();
 
-const getResourceRowsForMemo = async (db: D1Database, memoId: string): Promise<ResourceRow[]> => {
+const getResourceRowsForMemo = async (db: D1Database, workspaceId: string, memoId: string): Promise<ResourceRow[]> => {
   const rows = await db
     .prepare(
-      `SELECT id, memo_id, original_memo_id, bucket_name, object_key, kind, mime_type,
-              filename, byte_size, sha256, width, height, created_at, updated_at
-       FROM resources
-       WHERE memo_id = ?`
+      `SELECT r.id, r.memo_id, r.original_memo_id, r.bucket_name, r.object_key, r.kind, r.mime_type,
+              r.filename, r.byte_size, r.sha256, r.width, r.height, r.created_at, r.updated_at
+       FROM resources r
+       INNER JOIN memos m ON m.id = r.memo_id
+       WHERE r.memo_id = ? AND m.workspace_id = ?`
     )
-    .bind(memoId)
+    .bind(memoId, workspaceId)
     .all<ResourceRow>();
 
   return rows.results;
 };
 
-const listResourcesForMemo = async (db: D1Database, memoId: string): Promise<Resource[]> => {
+const listResourcesForMemo = async (db: D1Database, workspaceId: string, memoId: string): Promise<Resource[]> => {
   const rows = await db
     .prepare(
       `SELECT id, memo_id, original_memo_id, bucket_name, object_key, kind, mime_type,
               filename, byte_size, sha256, width, height, created_at, updated_at
-       FROM resources
-       WHERE memo_id = ? AND is_deleted = 0
-       ORDER BY created_at ASC, id ASC`
+       FROM resources r
+       INNER JOIN memos m ON m.id = r.memo_id
+       WHERE r.memo_id = ? AND m.workspace_id = ? AND r.is_deleted = 0
+       ORDER BY r.created_at ASC, r.id ASC`
     )
-    .bind(memoId)
+    .bind(memoId, workspaceId)
     .all<ResourceRow>();
 
   return rows.results.map(mapResource);
 };
 
-const listResourcesForMcp = async (db: D1Database, limit: number) => {
+const listResourcesForMcp = async (db: D1Database, workspaceId: string, limit: number) => {
   const [rows, stats] = await Promise.all([
     db
       .prepare(
@@ -5468,12 +5753,12 @@ const listResourcesForMcp = async (db: D1Database, limit: number) => {
                 r.created_at, r.updated_at, m.title AS memo_title, m.excerpt AS memo_excerpt,
                 m.is_deleted AS memo_is_deleted
          FROM resources r
-         LEFT JOIN memos m ON m.id = r.memo_id
-         WHERE r.is_deleted = 0
+         INNER JOIN memos m ON m.id = r.memo_id
+         WHERE m.workspace_id = ? AND r.is_deleted = 0
          ORDER BY r.created_at DESC
          LIMIT ?`
       )
-      .bind(limit)
+      .bind(workspaceId, limit)
       .all<ResourceListRow>(),
     db
       .prepare(
@@ -5481,10 +5766,11 @@ const listResourcesForMcp = async (db: D1Database, limit: number) => {
                 COALESCE(SUM(byte_size), 0) AS total_bytes,
                 COALESCE(SUM(CASE WHEN kind = 'image' THEN 1 ELSE 0 END), 0) AS image_count,
                 COALESCE(SUM(CASE WHEN kind = 'attachment' THEN 1 ELSE 0 END), 0) AS attachment_count
-         FROM resources
-         WHERE is_deleted = 0`
+         FROM resources r
+         INNER JOIN memos m ON m.id = r.memo_id
+         WHERE m.workspace_id = ? AND r.is_deleted = 0`
       )
-      .first<ResourceStatsRow>(),
+      .bind(workspaceId).first<ResourceStatsRow>(),
   ]);
 
   return {
@@ -5493,7 +5779,7 @@ const listResourcesForMcp = async (db: D1Database, limit: number) => {
   };
 };
 
-const getWorkspaceStats = async (db: D1Database) => {
+const getWorkspaceStats = async (db: D1Database, workspaceId: string) => {
   const [memoCounts, notebookCount, tagCount, resourceStats] = await Promise.all([
     db
       .prepare(
@@ -5503,27 +5789,28 @@ const getWorkspaceStats = async (db: D1Database) => {
            COALESCE(SUM(CASE WHEN is_deleted = 1 THEN 1 ELSE 0 END), 0) AS trashed,
            COALESCE(SUM(CASE WHEN is_deleted = 0 AND is_pinned = 1 THEN 1 ELSE 0 END), 0) AS pinned,
            COALESCE(SUM(CASE WHEN is_deleted = 0 AND tags_json = '[]' THEN 1 ELSE 0 END), 0) AS untagged
-         FROM memos`
+         FROM memos WHERE workspace_id = ?`
       )
-      .first<{ total: number; active: number; trashed: number; pinned: number; untagged: number }>(),
-    db.prepare(`SELECT COUNT(*) AS count FROM notebooks WHERE is_deleted = 0`).first<{ count: number }>(),
+      .bind(workspaceId).first<{ total: number; active: number; trashed: number; pinned: number; untagged: number }>(),
+    db.prepare(`SELECT COUNT(*) AS count FROM notebooks WHERE workspace_id = ? AND is_deleted = 0`).bind(workspaceId).first<{ count: number }>(),
     db
       .prepare(
         `SELECT COUNT(DISTINCT json_each.value) AS count
          FROM memos m, json_each(m.tags_json)
-         WHERE m.is_deleted = 0 AND trim(json_each.value) <> ''`
+         WHERE m.workspace_id = ? AND m.is_deleted = 0 AND trim(json_each.value) <> ''`
       )
-      .first<{ count: number }>(),
+      .bind(workspaceId).first<{ count: number }>(),
     db
       .prepare(
         `SELECT COUNT(*) AS total_count,
                 COALESCE(SUM(byte_size), 0) AS total_bytes,
                 COALESCE(SUM(CASE WHEN kind = 'image' THEN 1 ELSE 0 END), 0) AS image_count,
                 COALESCE(SUM(CASE WHEN kind = 'attachment' THEN 1 ELSE 0 END), 0) AS attachment_count
-         FROM resources
-         WHERE is_deleted = 0`
+         FROM resources r
+         INNER JOIN memos m ON m.id = r.memo_id
+         WHERE m.workspace_id = ? AND r.is_deleted = 0`
       )
-      .first<ResourceStatsRow>(),
+      .bind(workspaceId).first<ResourceStatsRow>(),
   ]);
 
   return {
diff --git a/apps/web/src/components/SettingsPane.tsx b/apps/web/src/components/SettingsPane.tsx
index 88157a41..efc5e3b4 100644
--- a/apps/web/src/components/SettingsPane.tsx
+++ b/apps/web/src/components/SettingsPane.tsx
@@ -12,6 +12,7 @@ import { PreferenceCard } from "./settings/PreferenceCard";
 import { PasswordCard } from "./settings/PasswordCard";
 import { SessionCard } from "./settings/SessionCard";
 import { SystemInfoCard } from "./settings/SystemInfoCard";
+import { UserManagementCard } from "./settings/UserManagementCard";
 import { ThemeToggle } from "./ThemeToggle";
 
 interface SettingsPaneProps {
@@ -23,6 +24,7 @@ interface SettingsPaneProps {
   onLogout: () => void;
   isLoggingOut: boolean;
   authRequired: boolean;
+  isOwner: boolean;
   onShowGuide?: () => void;
 }
 
@@ -41,6 +43,7 @@ export const SettingsPane = ({
   onLogout,
   isLoggingOut,
   authRequired,
+  isOwner,
   onShowGuide,
 }: SettingsPaneProps) => {
   const { t } = useTranslation();
@@ -84,6 +87,7 @@ export const SettingsPane = ({
             <McpConfigCard />
           </SettingsGroup>
           <SettingsGroup>
+            {isOwner ? <UserManagementCard /> : null}
             <PasswordCard authRequired={authRequired} />
             <SystemInfoCard />
             <SessionCard authRequired={authRequired} isLoggingOut={isLoggingOut} onLogout={onLogout} />
diff --git a/apps/web/src/components/WorkspaceApp.tsx b/apps/web/src/components/WorkspaceApp.tsx
index 216cb9ca..0d26b9ba 100644
--- a/apps/web/src/components/WorkspaceApp.tsx
+++ b/apps/web/src/components/WorkspaceApp.tsx
@@ -2571,6 +2571,7 @@ export const WorkspaceApp = ({
                     onLogout={onLogout}
                     isLoggingOut={isLoggingOut}
                     authRequired={authRequired}
+                    isOwner={authRequired && user?.role === "owner"}
                     onShowGuide={() => setRightView("evernote-migration")}
                   />
                 ) : rightView === "assets" ? (
diff --git a/apps/web/src/components/settings/UserManagementCard.tsx b/apps/web/src/components/settings/UserManagementCard.tsx
new file mode 100644
index 00000000..abb78813
--- /dev/null
+++ b/apps/web/src/components/settings/UserManagementCard.tsx
@@ -0,0 +1,201 @@
+import { useState, type FormEvent } from "react";
+import { useMutation, useQuery, useQueryClient } from "@tanstack/react-query";
+import { KeyRound, UserPlus, Users } from "lucide-react";
+import { useTranslation } from "react-i18next";
+import type { InstanceUser } from "@edgeever/shared";
+import { Button } from "@/components/ui/button";
+import { Card, CardContent, CardDescription, CardHeader, CardTitle } from "@/components/ui/card";
+import { Dialog, DialogClose, DialogContent, DialogDescription, DialogFooter, DialogHeader, DialogTitle } from "@/components/ui/dialog";
+import { Input } from "@/components/ui/input";
+import { Switch } from "@/components/ui/switch";
+import { ApiRequestError, api } from "@/lib/api";
+
+export const UserManagementCard = () => {
+  const { t } = useTranslation();
+  const queryClient = useQueryClient();
+  const [createOpen, setCreateOpen] = useState(false);
+  const [resetUser, setResetUser] = useState<InstanceUser | null>(null);
+  const [username, setUsername] = useState("");
+  const [displayName, setDisplayName] = useState("");
+  const [password, setPassword] = useState("");
+  const [resetPassword, setResetPassword] = useState("");
+
+  const usersQuery = useQuery({ queryKey: ["users"], queryFn: api.listUsers });
+  const refresh = () => queryClient.invalidateQueries({ queryKey: ["users"] });
+  const createMutation = useMutation({
+    mutationFn: api.createUser,
+    onSuccess: () => {
+      setCreateOpen(false);
+      setUsername("");
+      setDisplayName("");
+      setPassword("");
+      void refresh();
+    },
+  });
+  const updateMutation = useMutation({
+    mutationFn: ({ userId, input }: { userId: string; input: { password?: string; isDisabled?: boolean } }) =>
+      api.updateUser(userId, input),
+    onSuccess: () => void refresh(),
+  });
+
+  const handleCreate = (event: FormEvent) => {
+    event.preventDefault();
+    createMutation.mutate({ username, displayName: displayName || null, password });
+  };
+
+  const handleCreateOpenChange = (open: boolean) => {
+    setCreateOpen(open);
+    if (!open) {
+      setUsername("");
+      setDisplayName("");
+      setPassword("");
+      createMutation.reset();
+    }
+  };
+
+  const createError =
+    createMutation.error instanceof ApiRequestError && createMutation.error.code === "username_exists"
+      ? t("users.usernameExists")
+      : t("users.failed");
+
+  const handleReset = (event: FormEvent) => {
+    event.preventDefault();
+    if (!resetUser) return;
+    updateMutation.mutate(
+      { userId: resetUser.id, input: { password: resetPassword } },
+      { onSuccess: () => { setResetUser(null); setResetPassword(""); } },
+    );
+  };
+
+  return (
+    <>
+      <Card className="w-full min-w-0 overflow-hidden shadow-none">
+        <CardHeader className="p-4">
+          <div className="flex items-start justify-between gap-3">
+            <div>
+              <CardTitle className="flex items-center gap-2 text-sm">
+                <Users className="h-4 w-4 text-emerald-700" />
+                {t("users.title")}
+              </CardTitle>
+              <CardDescription className="mt-1">{t("users.description")}</CardDescription>
+            </div>
+            <Button size="sm" onClick={() => setCreateOpen(true)}>
+              <UserPlus className="h-4 w-4" /> {t("users.create")}
+            </Button>
+          </div>
+        </CardHeader>
+        <CardContent className="grid gap-2 p-4 pt-0">
+          {usersQuery.isLoading ? <p className="text-sm text-slate-500">{t("users.loading")}</p> : null}
+          {usersQuery.data?.users.map((user) => (
+            <div key={user.id} className="flex flex-wrap items-center justify-between gap-3 rounded-lg border border-slate-200 p-3">
+              <div className="min-w-0">
+                <p className="truncate text-sm font-semibold text-slate-800">{user.displayName || user.username}</p>
+                <p className="truncate text-xs text-slate-500">@{user.username} · {t(`users.roles.${user.role}`)}</p>
+              </div>
+              <div className="flex items-center gap-3">
+                <Button size="sm" variant="outline" onClick={() => setResetUser(user)}>
+                  <KeyRound className="h-3.5 w-3.5" /> {t("users.resetPassword")}
+                </Button>
+                {user.role !== "owner" ? (
+                  <label className="flex items-center gap-2 text-xs text-slate-600">
+                    {user.isDisabled ? t("users.disabled") : t("users.enabled")}
+                    <Switch
+                      checked={!user.isDisabled}
+                      disabled={updateMutation.isPending}
+                      onCheckedChange={(checked) => updateMutation.mutate({ userId: user.id, input: { isDisabled: !checked } })}
+                    />
+                  </label>
+                ) : null}
+              </div>
+            </div>
+          ))}
+          {usersQuery.isError || createMutation.isError || updateMutation.isError ? (
+            <p className="text-xs font-medium text-rose-600">{t("users.failed")}</p>
+          ) : null}
+        </CardContent>
+      </Card>
+
+      <Dialog open={createOpen} onOpenChange={handleCreateOpenChange}>
+        <DialogContent className="max-w-md gap-0 overflow-hidden p-0">
+          <DialogHeader className="border-b border-slate-100 px-6 py-5 pr-12">
+            <DialogTitle>{t("users.createTitle")}</DialogTitle>
+            <DialogDescription className="leading-6">{t("users.createDescription")}</DialogDescription>
+          </DialogHeader>
+          <form className="grid gap-5 px-6 py-5" autoComplete="off" onSubmit={handleCreate}>
+            <label className="grid gap-2 text-sm font-medium text-slate-700" htmlFor="edgeever-new-account-username">
+              {t("users.username")}
+              <Input
+                id="edgeever-new-account-username"
+                name="edgeever-new-account-username"
+                autoComplete="off"
+                autoCapitalize="none"
+                spellCheck={false}
+                data-1p-ignore
+                data-lpignore="true"
+                value={username}
+                onChange={(event) => setUsername(event.target.value)}
+                placeholder={t("users.usernamePlaceholder")}
+                required
+                maxLength={80}
+              />
+            </label>
+            <label className="grid gap-2 text-sm font-medium text-slate-700" htmlFor="edgeever-new-account-display-name">
+              {t("users.displayName")}
+              <Input
+                id="edgeever-new-account-display-name"
+                name="edgeever-new-account-display-name"
+                autoComplete="off"
+                data-1p-ignore
+                data-lpignore="true"
+                value={displayName}
+                onChange={(event) => setDisplayName(event.target.value)}
+                placeholder={t("users.displayNamePlaceholder")}
+                maxLength={80}
+              />
+            </label>
+            <label className="grid gap-2 text-sm font-medium text-slate-700" htmlFor="edgeever-new-account-password">
+              {t("users.password")}
+              <Input
+                id="edgeever-new-account-password"
+                name="edgeever-new-account-password"
+                type="password"
+                autoComplete="new-password"
+                data-1p-ignore
+                data-lpignore="true"
+                value={password}
+                onChange={(event) => setPassword(event.target.value)}
+                placeholder={t("users.passwordPlaceholder")}
+                minLength={8}
+                required
+              />
+              <span className="text-xs font-normal text-slate-500">{t("users.passwordHint")}</span>
+            </label>
+            {createMutation.isError ? <p className="text-sm font-medium text-rose-600" role="alert">{createError}</p> : null}
+            <DialogFooter className="mt-1 gap-2 sm:space-x-0">
+              <DialogClose asChild><Button type="button" variant="outline">{t("common.cancel")}</Button></DialogClose>
+              <Button type="submit" variant="solid" disabled={createMutation.isPending}>
+                {createMutation.isPending ? t("users.creating") : t("users.create")}
+              </Button>
+            </DialogFooter>
+          </form>
+        </DialogContent>
+      </Dialog>
+
+      <Dialog open={Boolean(resetUser)} onOpenChange={(open) => { if (!open) setResetUser(null); }}>
+        <DialogContent className="max-w-md">
+          <DialogHeader><DialogTitle>{t("users.resetTitle", { username: resetUser?.username })}</DialogTitle><DialogDescription>{t("users.resetDescription")}</DialogDescription></DialogHeader>
+          <form className="grid gap-4" autoComplete="off" onSubmit={handleReset}>
+            <label className="grid gap-2 text-sm font-medium text-slate-700" htmlFor="edgeever-reset-account-password">
+              {t("users.newPassword")}
+              <Input id="edgeever-reset-account-password" name="edgeever-reset-account-password" type="password" autoComplete="new-password" value={resetPassword} onChange={(event) => setResetPassword(event.target.value)} placeholder={t("users.passwordPlaceholder")} minLength={8} required />
+            </label>
+            <DialogFooter className="gap-2 sm:space-x-0">
+              <DialogClose asChild><Button type="button" variant="outline">{t("common.cancel")}</Button></DialogClose>
+              <Button type="submit" variant="solid" disabled={updateMutation.isPending}>{t("users.resetPassword")}</Button>
+            </DialogFooter>
+          </form>
+        </DialogContent>
+      </Dialog>
+    </>
+  );
+};
diff --git a/apps/web/src/i18n/resources/en-US.ts b/apps/web/src/i18n/resources/en-US.ts
index 529a69e6..8f71fb68 100644
--- a/apps/web/src/i18n/resources/en-US.ts
+++ b/apps/web/src/i18n/resources/en-US.ts
@@ -542,6 +542,31 @@ export const enUS = {
     loggingOut: "Signing out...",
     logout: "Sign out",
   },
+  users: {
+    title: "User accounts",
+    description: "Create isolated personal note spaces for family or team members. Public registration stays disabled.",
+    loading: "Loading accounts...",
+    create: "Create account",
+    creating: "Creating...",
+    createTitle: "Create account",
+    createDescription: "The account gets isolated notes, attachments, Trash, and MCP tokens.",
+    username: "Username",
+    usernamePlaceholder: "For example: alex",
+    usernameExists: "That username already exists. Choose another one.",
+    displayName: "Display name",
+    displayNamePlaceholder: "Optional, for example: Alex",
+    password: "Initial password",
+    passwordPlaceholder: "Enter at least 8 characters",
+    passwordHint: "The member can change this password in Profile after signing in.",
+    newPassword: "New password (8+ characters)",
+    resetPassword: "Reset password",
+    resetTitle: "Reset password for {{username}}",
+    resetDescription: "Other sessions for this account will be revoked after the reset.",
+    enabled: "Enabled",
+    disabled: "Disabled",
+    failed: "The account operation failed. Check the input and try again.",
+    roles: { owner: "Instance owner", member: "Member" },
+  },
   password: {
     title: "Change password",
     description: "Your current device stays signed in; other sessions will be signed out.",
diff --git a/apps/web/src/i18n/resources/zh-CN.ts b/apps/web/src/i18n/resources/zh-CN.ts
index fa1ae025..6c70a485 100644
--- a/apps/web/src/i18n/resources/zh-CN.ts
+++ b/apps/web/src/i18n/resources/zh-CN.ts
@@ -542,6 +542,31 @@ export const zhCN = {
     loggingOut: "安全退出中...",
     logout: "退出登录",
   },
+  users: {
+    title: "账号管理",
+    description: "为家人或团队成员创建独立的个人笔记空间。实例不开放公开注册。",
+    loading: "正在加载账号...",
+    create: "创建账号",
+    creating: "正在创建...",
+    createTitle: "创建新账号",
+    createDescription: "新账号会获得完全独立的笔记、附件、回收站和 MCP Token。",
+    username: "登录账号",
+    usernamePlaceholder: "例如：xiaoming",
+    usernameExists: "这个登录账号已经存在，请换一个名称。",
+    displayName: "显示名称",
+    displayNamePlaceholder: "选填，例如：小明",
+    password: "初始密码",
+    passwordPlaceholder: "请输入至少 8 位密码",
+    passwordHint: "成员首次登录后可以在个人中心修改密码。",
+    newPassword: "新密码（至少 8 位）",
+    resetPassword: "重置密码",
+    resetTitle: "重置 {{username}} 的密码",
+    resetDescription: "重置后，该账号在其他设备上的登录会话将失效。",
+    enabled: "已启用",
+    disabled: "已停用",
+    failed: "账号操作失败，请检查输入后重试。",
+    roles: { owner: "实例管理员", member: "成员" },
+  },
   password: {
     title: "修改密码",
     description: "修改后会保留当前设备登录，并退出其他设备上的登录会话。",
diff --git a/apps/web/src/lib/api.ts b/apps/web/src/lib/api.ts
index 6a72f6ad..963de24f 100644
--- a/apps/web/src/lib/api.ts
+++ b/apps/web/src/lib/api.ts
@@ -1,5 +1,6 @@
 import type {
   AuthSession,
+  InstanceUser,
   ApiToken,
   CreatedApiToken,
   JsonBackupMemo,
@@ -46,6 +47,9 @@ type ListApiTokensResponse = {
   availableScopes: string[];
 };
 
+type ListUsersResponse = { users: InstanceUser[] };
+type UserResponse = { user: InstanceUser };
+
 type MemoResponse = {
   memo: MemoDetail;
 };
@@ -127,6 +131,20 @@ export const api = {
       body: JSON.stringify(payload),
     }),
 
+  listUsers: () => request<ListUsersResponse>("/api/v1/users"),
+
+  createUser: (payload: { username: string; displayName?: string | null; password: string }) =>
+    request<UserResponse>("/api/v1/users", {
+      method: "POST",
+      body: JSON.stringify(payload),
+    }),
+
+  updateUser: (userId: string, payload: { displayName?: string | null; password?: string; isDisabled?: boolean }) =>
+    request<UserResponse>(`/api/v1/users/${userId}`, {
+      method: "PATCH",
+      body: JSON.stringify(payload),
+    }),
+
   logout: () =>
     request<{ ok: true }>("/api/v1/auth/logout", {
       method: "POST",
diff --git a/docs/openapi.json b/docs/openapi.json
index c8ee737e..1ab3481f 100644
--- a/docs/openapi.json
+++ b/docs/openapi.json
@@ -159,6 +159,47 @@
         }
       }
     },
+    "/api/v1/users": {
+      "get": {
+        "summary": "List instance users (owner only)",
+        "responses": {
+          "200": {
+            "description": "Instance user list",
+            "content": { "application/json": { "schema": {
+              "type": "object",
+              "properties": { "users": { "type": "array", "items": { "$ref": "#/components/schemas/InstanceUser" } } },
+              "required": ["users"]
+            } } }
+          },
+          "403": { "$ref": "#/components/responses/Error" }
+        }
+      },
+      "post": {
+        "summary": "Create an isolated user workspace (owner only)",
+        "requestBody": { "required": true, "content": { "application/json": { "schema": { "$ref": "#/components/schemas/UserCreateInput" } } } },
+        "responses": {
+          "201": { "description": "Created user", "content": { "application/json": { "schema": {
+            "type": "object", "properties": { "user": { "$ref": "#/components/schemas/InstanceUser" } }, "required": ["user"]
+          } } } },
+          "403": { "$ref": "#/components/responses/Error" },
+          "409": { "$ref": "#/components/responses/Error" }
+        }
+      }
+    },
+    "/api/v1/users/{id}": {
+      "patch": {
+        "summary": "Update, disable, or reset a user (owner only)",
+        "parameters": [{ "name": "id", "in": "path", "required": true, "schema": { "type": "string" } }],
+        "requestBody": { "required": true, "content": { "application/json": { "schema": { "$ref": "#/components/schemas/UserUpdateInput" } } } },
+        "responses": {
+          "200": { "description": "Updated user", "content": { "application/json": { "schema": {
+            "type": "object", "properties": { "user": { "$ref": "#/components/schemas/InstanceUser" } }, "required": ["user"]
+          } } } },
+          "403": { "$ref": "#/components/responses/Error" },
+          "404": { "$ref": "#/components/responses/Error" }
+        }
+      }
+    },
     "/api/v1/notebooks": {
       "get": {
         "summary": "List notebooks",
@@ -1261,9 +1302,45 @@
           },
           "displayName": {
             "type": ["string", "null"]
+          },
+          "role": {
+            "type": "string",
+            "enum": ["owner", "member"]
           }
         },
-        "required": ["id", "username", "displayName"]
+        "required": ["id", "username", "displayName", "role"]
+      },
+      "InstanceUser": {
+        "allOf": [
+          { "$ref": "#/components/schemas/AuthUser" },
+          {
+            "type": "object",
+            "properties": {
+              "isDisabled": { "type": "boolean" },
+              "lastLoginAt": { "type": ["string", "null"], "format": "date-time" },
+              "createdAt": { "type": "string", "format": "date-time" }
+            },
+            "required": ["isDisabled", "lastLoginAt", "createdAt"]
+          }
+        ]
+      },
+      "UserCreateInput": {
+        "type": "object",
+        "properties": {
+          "username": { "type": "string", "minLength": 1, "maxLength": 80 },
+          "displayName": { "type": ["string", "null"], "maxLength": 80 },
+          "password": { "type": "string", "minLength": 8, "maxLength": 512 }
+        },
+        "required": ["username", "password"]
+      },
+      "UserUpdateInput": {
+        "type": "object",
+        "properties": {
+          "displayName": { "type": ["string", "null"], "maxLength": 80 },
+          "password": { "type": "string", "minLength": 8, "maxLength": 512 },
+          "isDisabled": { "type": "boolean" }
+        },
+        "minProperties": 1
       },
       "LoginInput": {
         "type": "object",
diff --git a/migrations/0012_multi_user_workspaces.sql b/migrations/0012_multi_user_workspaces.sql
new file mode 100644
index 00000000..a22a1d5f
--- /dev/null
+++ b/migrations/0012_multi_user_workspaces.sql
@@ -0,0 +1,61 @@
+PRAGMA foreign_keys = ON;
+
+CREATE TABLE workspaces (
+  id TEXT PRIMARY KEY,
+  name TEXT NOT NULL CHECK (length(trim(name)) > 0),
+  is_personal INTEGER NOT NULL DEFAULT 1 CHECK (is_personal IN (0, 1)),
+  created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+  updated_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now'))
+);
+
+CREATE TABLE workspace_members (
+  workspace_id TEXT NOT NULL,
+  user_id TEXT NOT NULL,
+  role TEXT NOT NULL CHECK (role IN ('owner', 'member')),
+  created_at TEXT NOT NULL DEFAULT (strftime('%Y-%m-%dT%H:%M:%fZ', 'now')),
+  PRIMARY KEY (workspace_id, user_id),
+  FOREIGN KEY (workspace_id) REFERENCES workspaces(id)
+    ON UPDATE CASCADE
+    ON DELETE CASCADE,
+  FOREIGN KEY (user_id) REFERENCES users(id)
+    ON UPDATE CASCADE
+    ON DELETE CASCADE
+);
+
+CREATE UNIQUE INDEX idx_workspace_members_personal_user
+  ON workspace_members(user_id);
+
+CREATE INDEX idx_workspace_members_workspace
+  ON workspace_members(workspace_id, role);
+
+CREATE UNIQUE INDEX idx_workspace_single_owner
+  ON workspace_members(workspace_id)
+  WHERE role = 'owner';
+
+INSERT INTO workspaces (id, name, is_personal)
+VALUES ('ws_default', 'Personal workspace', 1);
+
+-- Existing EdgeEver instances were single-user. Their first enabled user owns
+-- the legacy workspace; if no user exists yet, the login bootstrap claims it.
+INSERT OR IGNORE INTO workspace_members (workspace_id, user_id, role)
+SELECT 'ws_default', id, 'owner'
+FROM users
+WHERE is_disabled = 0
+ORDER BY created_at ASC
+LIMIT 1;
+
+ALTER TABLE notebooks ADD COLUMN workspace_id TEXT NOT NULL DEFAULT 'ws_default';
+ALTER TABLE memos ADD COLUMN workspace_id TEXT NOT NULL DEFAULT 'ws_default';
+ALTER TABLE api_tokens ADD COLUMN workspace_id TEXT NOT NULL DEFAULT 'ws_default';
+
+CREATE INDEX idx_notebooks_workspace_parent
+  ON notebooks(workspace_id, parent_id, is_deleted, sort_order, name);
+
+CREATE INDEX idx_memos_workspace_notebook_feed
+  ON memos(workspace_id, notebook_id, is_deleted, updated_at DESC);
+
+CREATE INDEX idx_memos_workspace_archive_feed
+  ON memos(workspace_id, is_archived, is_deleted, updated_at DESC);
+
+CREATE INDEX idx_api_tokens_workspace
+  ON api_tokens(workspace_id, is_revoked, created_at DESC);
diff --git a/packages/shared/src/schemas.ts b/packages/shared/src/schemas.ts
index 6661fbe6..449b4a9b 100644
--- a/packages/shared/src/schemas.ts
+++ b/packages/shared/src/schemas.ts
@@ -67,6 +67,20 @@ export const ChangePasswordSchema = z
     path: ["confirmPassword"],
   });
 
+export const UserCreateSchema = z.object({
+  username: z.string().trim().min(1).max(80),
+  displayName: z.string().trim().max(80).nullable().optional(),
+  password: z.string().min(8).max(512),
+});
+
+export const UserUpdateSchema = z
+  .object({
+    displayName: z.string().trim().max(80).nullable().optional(),
+    password: z.string().min(8).max(512).optional(),
+    isDisabled: z.boolean().optional(),
+  })
+  .refine((input) => Object.keys(input).length > 0, "At least one field is required.");
+
 export const ApiTokenCreateSchema = z.object({
   name: z.string().trim().min(1).max(80),
   scopes: z.array(z.string().trim().min(1).max(80)).min(1).max(32),
@@ -86,5 +100,7 @@ export type DeleteMemosInput = z.infer<typeof DeleteMemosSchema>;
 export type MergeMemosInput = z.infer<typeof MergeMemosSchema>;
 export type LoginInput = z.infer<typeof LoginSchema>;
 export type ChangePasswordInput = z.infer<typeof ChangePasswordSchema>;
+export type UserCreateInput = z.infer<typeof UserCreateSchema>;
+export type UserUpdateInput = z.infer<typeof UserUpdateSchema>;
 export type ApiTokenCreateInput = z.infer<typeof ApiTokenCreateSchema>;
 export type TagRenameInput = z.infer<typeof TagRenameSchema>;
diff --git a/packages/shared/src/types.ts b/packages/shared/src/types.ts
index 99108629..47689c77 100644
--- a/packages/shared/src/types.ts
+++ b/packages/shared/src/types.ts
@@ -117,6 +117,13 @@ export type AuthUser = {
   id: string;
   username: string;
   displayName: string | null;
+  role: "owner" | "member";
+};
+
+export type InstanceUser = AuthUser & {
+  isDisabled: boolean;
+  lastLoginAt: string | null;
+  createdAt: string;
 };
 
 export type AuthSession = {