feat(frontend): 进来即写——落地页「直接开始写」直达空白编辑器，敲字后延迟落库

Phase 0（写作工作台重构）：新增 /write 草稿编辑器入口，只有敲入实质正文并停顿后
才懒建占位「未命名草稿」项目并种入首章草稿（useDeferredDraft，双重幂等闸 + 草稿落库
非致命降级），随即 replace 换入完整工作台；空进空出不落库，杜绝孤儿草稿。
落地页 CTA 改为「直接开始写」为主、「先立项」（立项向导）为辅。

apps/web/app/page.tsx

@@ -1,5 +1,5 @@
 import Link from "next/link";
-import { BookOpen, Plus } from "lucide-react";
+import { BookOpen, PenLine, Plus } from "lucide-react";
 
 import { AppShell } from "@/components/AppShell";
 import { BackendDownNotice } from "@/components/BackendDownNotice";
@@ -28,13 +28,22 @@ export default async function DashboardPage() {
           title="我的作品"
           description="从一个灵感进入正文、设定、审稿与验收闭环。"
           actions={
-            <Link
-              href="/projects/new"
-              className={buttonClass({ variant: "primary" })}
-            >
-              <Plus className="h-4 w-4" aria-hidden="true" />
-              新建作品
-            </Link>
+            <div className="flex flex-wrap items-center gap-2">
+              <Link
+                href="/write"
+                className={buttonClass({ variant: "primary" })}
+              >
+                <PenLine className="h-4 w-4" aria-hidden="true" />
+                直接开始写
+              </Link>
+              <Link
+                href="/projects/new"
+                className={buttonClass({ variant: "secondary" })}
+              >
+                <Plus className="h-4 w-4" aria-hidden="true" />
+                先立项
+              </Link>
+            </div>
           }
         />
 
@@ -44,15 +53,24 @@ export default async function DashboardPage() {
           <EmptyState
             icon={BookOpen}
             title="还没有作品"
-            description="从一句灵感开始，后续的设定库、大纲、写章和审稿都会围绕这本书展开。"
+            description="直接开始写，落笔即成书；或先立项，从一句灵感搭好设定、大纲再动笔。"
             action={
-              <Link
-                href="/projects/new"
-                className={buttonClass({ variant: "primary" })}
-              >
-                <Plus className="h-4 w-4" aria-hidden="true" />
-                新建作品
-              </Link>
+              <div className="flex flex-wrap items-center justify-center gap-2">
+                <Link
+                  href="/write"
+                  className={buttonClass({ variant: "primary" })}
+                >
+                  <PenLine className="h-4 w-4" aria-hidden="true" />
+                  直接开始写
+                </Link>
+                <Link
+                  href="/projects/new"
+                  className={buttonClass({ variant: "secondary" })}
+                >
+                  <Plus className="h-4 w-4" aria-hidden="true" />
+                  先立项
+                </Link>
+              </div>
             }
           />
         ) : (

apps/web/app/write/page.tsx

@@ -0,0 +1,6 @@
+import { DraftComposer } from "@/components/start/DraftComposer";
+
+// 进来即写入口（无 project 前缀）：直达空白编辑器，敲字后懒建项目并换入 /projects/[id]/write。
+export default function WriteDraftPage() {
+  return <DraftComposer />;
+}

apps/web/components/start/DraftComposer.tsx

@@ -0,0 +1,58 @@
+"use client";
+
+import { useRef, useState } from "react";
+import { useRouter } from "next/navigation";
+
+import { AppShell } from "@/components/AppShell";
+import { TextArea } from "@/components/ui/TextArea";
+import { useDeferredDraft } from "@/lib/start/useDeferredDraft";
+
+// 敲入正文后停顿多久才懒建项目（落库）——在停顿点落库，快照即所见，避免打断连续输入。
+const CREATE_DEBOUNCE_MS = 700;
+
+// 进来即写：空白编辑器直达。敲入实质正文并停顿后懒建占位项目 + 落首章草稿，随即换入完整工作台。
+// 空进空出不落库（从不敲字 → 从不 POST）。落库逻辑在 useDeferredDraft（已单测），此处只管交互。
+export function DraftComposer() {
+  const router = useRouter();
+  const { ensureCreated } = useDeferredDraft();
+  const [text, setText] = useState("");
+  const textRef = useRef("");
+  const timerRef = useRef<ReturnType<typeof setTimeout> | null>(null);
+  const redirectingRef = useRef(false);
+
+  const tryCreate = async (): Promise<void> => {
+    if (redirectingRef.current) return;
+    const snapshot = textRef.current;
+    if (snapshot.trim().length === 0) return;
+    const id = await ensureCreated(snapshot);
+    if (id && !redirectingRef.current) {
+      redirectingRef.current = true;
+      router.replace(`/projects/${id}/write`);
+    }
+  };
+
+  const onChange = (value: string): void => {
+    setText(value);
+    textRef.current = value;
+    if (timerRef.current) clearTimeout(timerRef.current);
+    timerRef.current = setTimeout(() => void tryCreate(), CREATE_DEBOUNCE_MS);
+  };
+
+  return (
+    <AppShell>
+      <div className="mx-auto flex min-h-[calc(100vh-var(--chrome,4rem))] max-w-3xl flex-col px-6 py-10 sm:px-8">
+        <p className="mb-4 text-sm text-ink-soft">
+          直接开始写——落笔即为你建立作品，正文自动保存。书名、设定、大纲都可在写作中随时补齐。
+        </p>
+        <TextArea
+          value={text}
+          onChange={(e) => onChange(e.target.value)}
+          className="min-h-[60vh] flex-1 resize-none text-lg leading-8"
+          placeholder="从这里开始写你的第一章……"
+          autoFocus
+          aria-label="正文"
+        />
+      </div>
+    </AppShell>
+  );
+}

apps/web/lib/start/useDeferredDraft.test.ts

@@ -0,0 +1,134 @@
+// @vitest-environment jsdom
+import { act, renderHook } from "@testing-library/react";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+
+import {
+  DRAFT_FIRST_CHAPTER,
+  DRAFT_PLACEHOLDER_TITLE,
+  useDeferredDraft,
+} from "./useDeferredDraft";
+
+// 后端客户端与 Toast 是 hook 的外部副作用边界，单测一律 mock。
+const post = vi.fn();
+const put = vi.fn();
+const toast = vi.fn();
+vi.mock("@/lib/api/client", () => ({
+  api: {
+    POST: (...a: unknown[]) => post(...a),
+    PUT: (...a: unknown[]) => put(...a),
+  },
+}));
+vi.mock("@/components/Toast", () => ({ useToast: () => toast }));
+
+describe("useDeferredDraft", () => {
+  beforeEach(() => {
+    post.mockReset();
+    put.mockReset();
+    toast.mockReset();
+  });
+  afterEach(() => vi.clearAllMocks());
+
+  it("初始为 idle", () => {
+    const { result } = renderHook(() => useDeferredDraft());
+    expect(result.current.status).toBe("idle");
+  });
+
+  it("首次落库：懒建占位项目 + 用已敲入正文种首章草稿，返回新项目 id", async () => {
+    post.mockResolvedValue({ data: { id: "p1" }, error: null });
+    put.mockResolvedValue({ data: {}, error: null });
+
+    const { result } = renderHook(() => useDeferredDraft());
+    let id: string | null = null;
+    await act(async () => {
+      id = await result.current.ensureCreated("第一段正文");
+    });
+
+    expect(id).toBe("p1");
+    expect(result.current.status).toBe("created");
+    expect(post).toHaveBeenCalledTimes(1);
+    expect(post).toHaveBeenCalledWith("/projects", {
+      body: { title: DRAFT_PLACEHOLDER_TITLE },
+    });
+    expect(put).toHaveBeenCalledWith(
+      "/projects/{project_id}/chapters/{chapter_no}/draft",
+      {
+        params: { path: { project_id: "p1", chapter_no: DRAFT_FIRST_CHAPTER } },
+        body: { text: "第一段正文" },
+      },
+    );
+    expect(toast).not.toHaveBeenCalled();
+  });
+
+  it("幂等：已建后再次调用复用同一 id，绝不重复 POST", async () => {
+    post.mockResolvedValue({ data: { id: "p1" }, error: null });
+    put.mockResolvedValue({ data: {}, error: null });
+
+    const { result } = renderHook(() => useDeferredDraft());
+    await act(async () => {
+      await result.current.ensureCreated("正文一");
+    });
+    let second: string | null = null;
+    await act(async () => {
+      second = await result.current.ensureCreated("正文二");
+    });
+
+    expect(second).toBe("p1");
+    expect(post).toHaveBeenCalledTimes(1);
+  });
+
+  it("正文为空白：仍懒建项目但跳过草稿落库", async () => {
+    post.mockResolvedValue({ data: { id: "p1" }, error: null });
+
+    const { result } = renderHook(() => useDeferredDraft());
+    await act(async () => {
+      await result.current.ensureCreated("   ");
+    });
+
+    expect(post).toHaveBeenCalledTimes(1);
+    expect(put).not.toHaveBeenCalled();
+  });
+
+  it("创建失败：status=error、弹错误 toast、返回 null、不落草稿", async () => {
+    post.mockResolvedValue({ data: null, error: { detail: "配额不足" } });
+
+    const { result } = renderHook(() => useDeferredDraft());
+    let id: string | null = "sentinel";
+    await act(async () => {
+      id = await result.current.ensureCreated("正文");
+    });
+
+    expect(id).toBeNull();
+    expect(result.current.status).toBe("error");
+    expect(put).not.toHaveBeenCalled();
+    expect(toast).toHaveBeenCalledWith(expect.any(String), "error");
+  });
+
+  it("草稿落库失败为非致命：项目已建仍返回 id，提示但不阻断", async () => {
+    post.mockResolvedValue({ data: { id: "p1" }, error: null });
+    put.mockResolvedValue({ data: null, error: { detail: "写库失败" } });
+
+    const { result } = renderHook(() => useDeferredDraft());
+    let id: string | null = null;
+    await act(async () => {
+      id = await result.current.ensureCreated("正文");
+    });
+
+    expect(id).toBe("p1");
+    expect(result.current.status).toBe("created");
+    expect(toast).toHaveBeenCalledWith(expect.any(String), "info");
+  });
+
+  it("请求抛异常：status=error、弹网络异常 toast、返回 null", async () => {
+    post.mockRejectedValue(new Error("network down"));
+
+    const { result } = renderHook(() => useDeferredDraft());
+    let id: string | null = "sentinel";
+    await act(async () => {
+      id = await result.current.ensureCreated("正文");
+    });
+
+    expect(id).toBeNull();
+    expect(result.current.status).toBe("error");
+    expect(toast).toHaveBeenCalledWith(expect.any(String), "error");
+  });
+});

apps/web/lib/start/useDeferredDraft.ts

@@ -0,0 +1,95 @@
+"use client";
+
+import { useCallback, useRef, useState } from "react";
+
+import { api } from "@/lib/api/client";
+import { useToast } from "@/components/Toast";
+
+// 进来即写（延迟落库）：落地页「直接开始写」直达空白编辑器，**只有敲入实质正文后**
+// 才懒建占位项目并把已敲入正文种进首章草稿。空进空出不落库，杜绝孤儿「未命名草稿」。
+export const DRAFT_PLACEHOLDER_TITLE = "未命名草稿";
+export const DRAFT_FIRST_CHAPTER = 1;
+
+export type DeferredStatus = "idle" | "creating" | "created" | "error";
+
+export interface UseDeferredDraft {
+  status: DeferredStatus;
+  // 首次有实质正文时调用：懒建占位项目 + 落首章草稿，返回新项目 id（调用方据此跳转编辑器）。
+  // 幂等：已建/在建时复用同一结果，绝不重复 POST。失败返回 null（不跳转）。
+  ensureCreated: (text: string) => Promise<string | null>;
+}
+
+export function useDeferredDraft(): UseDeferredDraft {
+  const [status, setStatus] = useState<DeferredStatus>("idle");
+  const toast = useToast();
+  // 已建项目 id 与在途 Promise：双重幂等闸，防抖多次触发只落一次库。
+  const createdIdRef = useRef<string | null>(null);
+  const inflightRef = useRef<Promise<string | null> | null>(null);
+
+  const ensureCreated = useCallback(
+    (text: string): Promise<string | null> => {
+      if (createdIdRef.current) return Promise.resolve(createdIdRef.current);
+      if (inflightRef.current) return inflightRef.current;
+
+      const run = createDraftProject(text, toast, setStatus).then((id) => {
+        inflightRef.current = null;
+        if (id) createdIdRef.current = id;
+        return id;
+      });
+      inflightRef.current = run;
+      return run;
+    },
+    [toast],
+  );
+
+  return { status, ensureCreated };
+}
+
+type Toast = ReturnType<typeof useToast>;
+
+// 懒建项目 + 落首章草稿（草稿失败为非致命：项目已建，正文仍在前端，进编辑器后自动重存）。
+async function createDraftProject(
+  text: string,
+  toast: Toast,
+  setStatus: (s: DeferredStatus) => void,
+): Promise<string | null> {
+  setStatus("creating");
+  try {
+    const { data, error } = await api.POST("/projects", {
+      body: { title: DRAFT_PLACEHOLDER_TITLE },
+    });
+    if (error || !data) {
+      setStatus("error");
+      toast("创建草稿失败，请重试", "error");
+      return null;
+    }
+    await seedFirstChapter(data.id, text, toast);
+    setStatus("created");
+    return data.id;
+  } catch {
+    setStatus("error");
+    toast("创建草稿异常，请检查网络", "error");
+    return null;
+  }
+}
+
+// 把已敲入正文种进首章草稿；空白正文跳过。落库失败仅提示、不抛（项目已建，不阻断进入编辑器）。
+async function seedFirstChapter(
+  projectId: string,
+  text: string,
+  toast: Toast,
+): Promise<void> {
+  if (text.trim().length === 0) return;
+  const { error } = await api.PUT(
+    "/projects/{project_id}/chapters/{chapter_no}/draft",
+    {
+      params: {
+        path: { project_id: projectId, chapter_no: DRAFT_FIRST_CHAPTER },
+      },
+      body: { text },
+    },
+  );
+  if (error) {
+    toast("首段草稿保存失败，进入编辑器后会自动重试", "info");
+  }
+}