diff --git a/apps/web/app/error.tsx b/apps/web/app/error.tsx
new file mode 100644
index 0000000..ed01afb
--- /dev/null
+++ b/apps/web/app/error.tsx
@@ -0,0 +1,37 @@
+"use client";
+
+import Link from "next/link";
+import { TriangleAlert } from "lucide-react";
+
+import { EmptyState } from "@/components/ui/EmptyState";
+import { Button } from "@/components/ui/Button";
+import { buttonClass } from "@/lib/ui/variants";
+
+interface ErrorBoundaryProps {
+  error: Error & { digest?: string };
+  reset: () => void;
+}
+
+export default function Error({ reset }: ErrorBoundaryProps) {
+  return (
+    <main className="flex min-h-screen items-center justify-center bg-bg px-6 py-16">
+      <div className="w-full max-w-md">
+        <EmptyState
+          icon={TriangleAlert}
+          title="出错了"
+          description="刚才的操作没能完成。可以重试，或先回到作品库。"
+          action={
+            <div className="flex items-center justify-center gap-2">
+              <Button variant="primary" onClick={reset}>
+                重试
+              </Button>
+              <Link href="/" className={buttonClass({ variant: "secondary" })}>
+                返回作品库
+              </Link>
+            </div>
+          }
+        />
+      </div>
+    </main>
+  );
+}
diff --git a/apps/web/app/loading.tsx b/apps/web/app/loading.tsx
new file mode 100644
index 0000000..9e27ca5
--- /dev/null
+++ b/apps/web/app/loading.tsx
@@ -0,0 +1,9 @@
+import { ThinkingIndicator } from "@/components/ThinkingIndicator";
+
+export default function Loading() {
+  return (
+    <main className="flex min-h-screen items-center justify-center bg-bg px-6 py-16">
+      <ThinkingIndicator label="加载中…" className="text-ink-soft" />
+    </main>
+  );
+}
diff --git a/apps/web/app/not-found.tsx b/apps/web/app/not-found.tsx
new file mode 100644
index 0000000..38e5f81
--- /dev/null
+++ b/apps/web/app/not-found.tsx
@@ -0,0 +1,24 @@
+import Link from "next/link";
+import { FileQuestion } from "lucide-react";
+
+import { EmptyState } from "@/components/ui/EmptyState";
+import { buttonClass } from "@/lib/ui/variants";
+
+export default function NotFound() {
+  return (
+    <main className="flex min-h-screen items-center justify-center bg-bg px-6 py-16">
+      <div className="w-full max-w-md">
+        <EmptyState
+          icon={FileQuestion}
+          title="页面不存在"
+          description="你要找的内容可能已被移动或从未存在。回到作品库继续创作吧。"
+          action={
+            <Link href="/" className={buttonClass({ variant: "primary" })}>
+              返回作品库
+            </Link>
+          }
+        />
+      </div>
+    </main>
+  );
+}
diff --git a/apps/web/components/Toast.tsx b/apps/web/components/Toast.tsx
index 78061c9..6959ea9 100644
--- a/apps/web/components/Toast.tsx
+++ b/apps/web/components/Toast.tsx
@@ -11,19 +11,51 @@ import {
   type ReactNode,
 } from "react";
 
+import { buttonClass } from "@/lib/ui/variants";
+
 type ToastKind = "info" | "error" | "success";
 
+interface ToastAction {
+  label: string;
+  onClick: () => void;
+}
+
+interface ToastOptions {
+  action?: ToastAction;
+  durationMs?: number;
+}
+
 interface ToastItem {
   id: number;
   message: string;
   kind: ToastKind;
+  action?: ToastAction;
 }
 
-type ShowToast = (message: string, kind?: ToastKind) => void;
+type ShowToast = (
+  message: string,
+  kind?: ToastKind,
+  options?: ToastOptions,
+) => void;
 
 const ToastContext = createContext<ShowToast | null>(null);
 
+// 普通提示 4s 自动消失；错误更需被看到，默认延长到 7s。
 const TOAST_TTL_MS = 4000;
+const ERROR_TOAST_TTL_MS = 7000;
+
+// 屏读前缀：让无视觉的用户也能区分提示性质。
+const SR_PREFIX: Record<ToastKind, string> = {
+  error: "错误：",
+  success: "成功：",
+  info: "",
+};
+
+function toastShellClass(kind: ToastKind): string {
+  if (kind === "error") return "border-conflict bg-panel text-conflict";
+  if (kind === "success") return "border-pass bg-panel text-pass";
+  return "border-line bg-panel text-ink";
+}
 
 export function ToastProvider({ children }: { children: ReactNode }) {
   const [items, setItems] = useState<ToastItem[]>([]);
@@ -32,13 +64,20 @@ export function ToastProvider({ children }: { children: ReactNode }) {
   // 在途定时器集合：卸载时统一清理，避免 setState-after-unmount 泄漏。
   const timersRef = useRef<Set<ReturnType<typeof setTimeout>>>(new Set());
 
-  const show = useCallback<ShowToast>((message, kind = "info") => {
+  const dismiss = useCallback((id: number) => {
+    setItems((prev) => prev.filter((t) => t.id !== id));
+  }, []);
+
+  const show = useCallback<ShowToast>((message, kind = "info", options) => {
     const id = nextIdRef.current++;
-    setItems((prev) => [...prev, { id, message, kind }]);
+    setItems((prev) => [...prev, { id, message, kind, action: options?.action }]);
+    const ttl =
+      options?.durationMs ??
+      (kind === "error" ? ERROR_TOAST_TTL_MS : TOAST_TTL_MS);
     const timer = setTimeout(() => {
       timersRef.current.delete(timer);
       setItems((prev) => prev.filter((t) => t.id !== id));
-    }, TOAST_TTL_MS);
+    }, ttl);
     timersRef.current.add(timer);
   }, []);
 
@@ -53,28 +92,46 @@ export function ToastProvider({ children }: { children: ReactNode }) {
 
   const value = useMemo(() => show, [show]);
 
+  const errorItems = items.filter((t) => t.kind === "error");
+  const politeItems = items.filter((t) => t.kind !== "error");
+
+  const renderItem = (t: ToastItem) => (
+    <div
+      key={t.id}
+      className={`pointer-events-auto flex items-center gap-3 rounded border px-4 py-2 text-sm shadow-paper ${toastShellClass(
+        t.kind,
+      )}`}
+    >
+      <span className="min-w-0">
+        <span className="sr-only">{SR_PREFIX[t.kind]}</span>
+        {t.message}
+      </span>
+      {t.action ? (
+        <button
+          type="button"
+          className={buttonClass({ variant: "ghost", size: "sm" })}
+          onClick={() => {
+            t.action?.onClick();
+            dismiss(t.id);
+          }}
+        >
+          {t.action.label}
+        </button>
+      ) : null}
+    </div>
+  );
+
   return (
     <ToastContext.Provider value={value}>
       {children}
-      <div
-        className="pointer-events-none fixed bottom-6 right-6 z-50 flex flex-col gap-2"
-        aria-live="polite"
-        role="status"
-      >
-        {items.map((t) => (
-          <div
-            key={t.id}
-            className={`pointer-events-auto rounded border px-4 py-2 text-sm shadow-paper ${
-              t.kind === "error"
-                ? "border-conflict bg-panel text-conflict"
-                : t.kind === "success"
-                  ? "border-pass bg-panel text-pass"
-                  : "border-line bg-panel text-ink"
-            }`}
-          >
-            {t.message}
-          </div>
-        ))}
+      {/* error 用 assertive 立即播报；其余 info/success 用 polite 礼貌播报。两区共用同一锚点容器避免重叠。 */}
+      <div className="pointer-events-none fixed bottom-6 right-6 z-50 flex flex-col gap-2">
+        <div className="flex flex-col gap-2" aria-live="assertive" role="alert">
+          {errorItems.map(renderItem)}
+        </div>
+        <div className="flex flex-col gap-2" aria-live="polite" role="status">
+          {politeItems.map(renderItem)}
+        </div>
       </div>
     </ToastContext.Provider>
   );
diff --git a/apps/web/lib/ui/useBodyScrollLock.test.ts b/apps/web/lib/ui/useBodyScrollLock.test.ts
new file mode 100644
index 0000000..b157f03
--- /dev/null
+++ b/apps/web/lib/ui/useBodyScrollLock.test.ts
@@ -0,0 +1,41 @@
+// @vitest-environment jsdom
+import { renderHook } from "@testing-library/react";
+import { afterEach, describe, expect, it } from "vitest";
+
+import { useBodyScrollLock } from "./useBodyScrollLock";
+
+describe("useBodyScrollLock", () => {
+  afterEach(() => {
+    document.body.style.overflow = "";
+  });
+
+  it("active 时锁定 body 滚动", () => {
+    renderHook(() => useBodyScrollLock(true));
+    expect(document.body.style.overflow).toBe("hidden");
+  });
+
+  it("active 为假时不改动 overflow", () => {
+    document.body.style.overflow = "scroll";
+    renderHook(() => useBodyScrollLock(false));
+    expect(document.body.style.overflow).toBe("scroll");
+  });
+
+  it("卸载时恢复原 overflow 值", () => {
+    document.body.style.overflow = "auto";
+    const { unmount } = renderHook(() => useBodyScrollLock(true));
+    expect(document.body.style.overflow).toBe("hidden");
+    unmount();
+    expect(document.body.style.overflow).toBe("auto");
+  });
+
+  it("active 由真转假时恢复原值", () => {
+    document.body.style.overflow = "visible";
+    const { rerender } = renderHook(
+      ({ active }: { active: boolean }) => useBodyScrollLock(active),
+      { initialProps: { active: true } },
+    );
+    expect(document.body.style.overflow).toBe("hidden");
+    rerender({ active: false });
+    expect(document.body.style.overflow).toBe("visible");
+  });
+});
diff --git a/apps/web/lib/ui/useBodyScrollLock.ts b/apps/web/lib/ui/useBodyScrollLock.ts
new file mode 100644
index 0000000..be7f4ee
--- /dev/null
+++ b/apps/web/lib/ui/useBodyScrollLock.ts
@@ -0,0 +1,20 @@
+"use client";
+
+import { useEffect } from "react";
+
+// 弹层（Drawer / CommandPalette / Modal）打开时锁定 body 滚动，关闭后恢复原值。
+// SSR 守卫：服务端无 document，直接跳过。
+export function useBodyScrollLock(active: boolean): void {
+  useEffect(() => {
+    if (!active) return;
+    if (typeof document === "undefined") return;
+
+    const { body } = document;
+    const previousOverflow = body.style.overflow;
+    body.style.overflow = "hidden";
+
+    return () => {
+      body.style.overflow = previousOverflow;
+    };
+  }, [active]);
+}
diff --git a/apps/web/lib/ui/variants.test.ts b/apps/web/lib/ui/variants.test.ts
index 6025c53..ddfaec7 100644
--- a/apps/web/lib/ui/variants.test.ts
+++ b/apps/web/lib/ui/variants.test.ts
@@ -4,7 +4,10 @@ import {
   badgeClass,
   buttonClass,
   cn,
+  focusRing,
   inputClass,
+  overlayScrim,
+  proseBody,
   segmentedClass,
   statusNoteClass,
 } from "./variants";
@@ -49,4 +52,22 @@ describe("ui variants", () => {
     expect(klass).toContain("inline-flex");
     expect(klass).toContain("border-line");
   });
+
+  it("shares the cinnabar focus ring with the button base", () => {
+    expect(focusRing).toContain("focus-visible:ring-2");
+    expect(focusRing).toContain("focus-visible:ring-cinnabar/35");
+    expect(buttonClass({ variant: "primary" })).toContain(focusRing);
+  });
+
+  it("renders manuscript body as serif 18px with airy leading", () => {
+    expect(proseBody).toContain("font-serif");
+    expect(proseBody).toContain("text-[18px]");
+    expect(proseBody).toContain("leading-[1.9]");
+  });
+
+  it("provides a full-screen overlay scrim below dialog chrome", () => {
+    expect(overlayScrim).toContain("fixed");
+    expect(overlayScrim).toContain("inset-0");
+    expect(overlayScrim).toContain("z-40");
+  });
 });
diff --git a/apps/web/lib/ui/variants.ts b/apps/web/lib/ui/variants.ts
index a95a992..133d4a6 100644
--- a/apps/web/lib/ui/variants.ts
+++ b/apps/web/lib/ui/variants.ts
@@ -23,6 +23,16 @@ export function cn(...classes: Array<string | false | null | undefined>): string
   return classes.filter(Boolean).join(" ");
 }
 
+// 统一焦点环（与 buttonBase 现有焦点环一致），供导航/输入等可聚焦元素复用。
+export const focusRing =
+  "focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-cinnabar/35";
+
+// 手稿正文统一排版：衬线 18px、行高 1.9。
+export const proseBody = "font-serif text-[18px] leading-[1.9]";
+
+// Drawer / CommandPalette 共用的全屏遮罩。
+export const overlayScrim = "fixed inset-0 z-40 bg-black/30";
+
 const buttonBase =
   "inline-flex items-center justify-center gap-1.5 rounded border text-sm transition-colors focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-cinnabar/35 disabled:cursor-not-allowed disabled:opacity-45";
 
diff --git a/apps/web/tailwind.config.ts b/apps/web/tailwind.config.ts
index 250211b..5cc4ceb 100644
--- a/apps/web/tailwind.config.ts
+++ b/apps/web/tailwind.config.ts
@@ -26,6 +26,9 @@ const config: Config = {
         sans: ['"Noto Sans SC"', '"PingFang SC"', "system-ui", "sans-serif"],
         mono: ['"JetBrains Mono"', "ui-monospace"],
       },
+      fontSize: {
+        "2xs": ["0.6875rem", { lineHeight: "1rem" }],
+      },
       borderRadius: { DEFAULT: "6px" },
       boxShadow: { paper: "0 1px 3px var(--shadow-paper)" },
       maxWidth: { prose: "720px" },