feat(backend): 整章重写 AI 反问澄清预检端点 rewrite/clarify（WFW-9 M2）

新增 POST /projects/{id}/chapters/{no}/rewrite/clarify（非流式 JSON）→ ClarifyDecision，
镜像 refine 侧 clarify：404 缺项目 → _build_rewrite_clarify_input（章级意见 + prior_draft
有界摘录 3000 字，不整章入 LLM）→ run_clarify(clarify_rewrite_spec, analyst 档) → 末尾
commit 落 usage_ledger → 返回决策。只读不写业务表（不变量 #3）；日志只记 feedback_len（脱敏）；
畸形 parsed 经 run_clarify 韧性回退 need_clarification=false（非 500）。新增 RewriteClarifyRequest
（feedback 必给、prior_draft 可选）。6 端点用例覆盖含糊/明确/404/fail-open/422/摘录有界不泄漏。

apps/api/ww_api/routers/projects.py

@@ -20,6 +20,7 @@ from typing import Annotated, Any
 from fastapi import APIRouter, BackgroundTasks, Depends, Request
 from fastapi.responses import StreamingResponse
 from sqlalchemy.ext.asyncio import AsyncSession
+from ww_agents import ClarifyDecision, clarify_rewrite_spec
 from ww_core.domain.chapter_repo import ChapterRepo
 from ww_core.domain.digest_repo import DigestAppendRepo
 from ww_core.domain.injection_repo import EntityRef, InjectionOverride, InjectionOverrideRepo
@@ -36,6 +37,7 @@ from ww_core.orchestrator import (
     error_event,
     normalize_deltas,
     normalize_review,
+    run_clarify,
     stream_chapter_draft,
     stream_chapter_rewrite,
 )
@@ -64,6 +66,7 @@ from ww_api.schemas.projects import (
     ReviewHistoryItem,
     ReviewHistoryResponse,
     ReviewRequest,
+    RewriteClarifyRequest,
     RewriteStreamRequest,
 )
 from ww_api.services.accept_service import (
@@ -76,6 +79,7 @@ from ww_api.services.digest_extraction import extract_digest_facts
 from ww_api.services.foreshadow_scan import SessionFactory, run_overdue_scan
 from ww_api.services.project_deps import (
     get_chapter_repo,
+    get_clarify_gateway,
     get_digest_append_repo,
     get_digest_gateway,
     get_injection_repo,
@@ -106,6 +110,7 @@ ChapterRepoDep = Annotated[ChapterRepo, Depends(get_chapter_repo)]
 GatewayDep = Annotated[Gateway, Depends(get_writer_gateway)]
 ReviewGatewayDep = Annotated[Gateway, Depends(get_review_gateway)]
 DigestGatewayDep = Annotated[Gateway, Depends(get_digest_gateway)]
+ClarifyGatewayDep = Annotated[Gateway, Depends(get_clarify_gateway)]
 MemoryReposDep = Annotated[MemoryRepos, Depends(get_memory_repos)]
 InjectionRepoDep = Annotated[InjectionOverrideRepo, Depends(get_injection_repo)]
 ReviewRepoDep = Annotated[ReviewRepo, Depends(get_review_repo)]
@@ -370,6 +375,80 @@ async def stream_rewrite(
     )
 
 
+# 整章重写预检的草稿摘录上界：只喂 analyst 预检**开头一小段**供锚定，绝不整章入 LLM
+# （守成本/上下文，且预检只需判意见含糊度、不需读全章）。
+_REWRITE_CLARIFY_EXCERPT_MAX = 3000
+
+
+def _build_rewrite_clarify_input(feedback: str, prior_draft: str | None) -> str:
+    """组整章重写预检输入：作者章级意见 + 当前章草稿的有界摘录（分块标注，供教条区分）。
+
+    只取 `prior_draft` 开头 `_REWRITE_CLARIFY_EXCERPT_MAX` 字符作锚定摘录——预检不需读全章，
+    避免把 200k 整章喂给 analyst 预检（成本/上下文/脱敏）。无草稿时只喂意见（退化，仍可判含糊）。
+    """
+    parts = [f"【作者的整章修改意见】\n{feedback}"]
+    if prior_draft:
+        excerpt = prior_draft[:_REWRITE_CLARIFY_EXCERPT_MAX]
+        parts.append(f"【当前章节草稿（摘录，仅供锚定）】\n{excerpt}")
+    return "\n\n".join(parts)
+
+
+@router.post(
+    "/{project_id}/chapters/{chapter_no}/rewrite/clarify",
+    responses={
+        404: {"model": ErrorEnvelope, "description": "项目不存在"},
+        503: {"model": ErrorEnvelope, "description": "LLM 不可用"},
+    },
+)
+async def clarify_rewrite(
+    project_id: uuid.UUID,
+    chapter_no: int,
+    body: RewriteClarifyRequest,
+    request: Request,
+    project_repo: ProjectRepoDep,
+    gateway: ClarifyGatewayDep,
+    session: Annotated[AsyncSession, Depends(get_session)],
+) -> ClarifyDecision:
+    """整章重写预检澄清（WFW-9 M2 路线A 两阶段之「问题」阶段）：非流式 JSON，只判不改。
+
+    镜像 refine 侧 clarify——只判「作者这条整章重写意见清不清楚」，含糊则反问 1 问 + 给选项，
+    清楚则给确认语放行；**绝不改正文**（整章重写仍走既有 rewrite SSE 端点）。analyst 档
+    （不变量 #2）。只取 `prior_draft` 有界摘录喂预检（不整章入 LLM）。
+
+    项目不存在 → 404（触网关前 fail-fast，同 rewrite/draft）；无凭据 → 503（dep 解析阶段拦下）。
+    **只读不写业务表**（不变量 #3）；末尾 `commit()` 让网关 usage_ledger 落库（add-only，否则
+    记账静默丢失，同 rewrite 纪律）。判别/校验失败在 `run_clarify` 内确定性回退
+    `need_clarification=false`（不阻塞整章重写主链路）。
+    """
+    request_id = getattr(request.state, "request_id", None)
+
+    if await project_repo.get(STUB_OWNER_ID, project_id) is None:
+        raise AppError(ErrorCode.NOT_FOUND, f"project not found: {project_id}")
+
+    context = _build_rewrite_clarify_input(body.feedback, body.prior_draft)
+    decision = await run_clarify(
+        clarify_rewrite_spec,  # 不变量 #2：analyst 档，不传 model
+        context=context,
+        gateway=gateway,
+        user_id=STUB_OWNER_ID,
+        project_id=project_id,
+    )
+
+    # 提交边界：只读不写业务表，但网关 ledger add-only → 端点末尾 commit（否则记账丢失）。
+    await session.commit()
+
+    log.info(
+        "rewrite_clarify_done",
+        project_id=str(project_id),
+        chapter_no=chapter_no,
+        request_id=request_id,
+        feedback_len=len(body.feedback),  # 脱敏：只记长度，不记正文（不变量/日志纪律）
+        need_clarification=decision.need_clarification,
+        question_count=len(decision.questions),
+    )
+    return decision
+
+
 @router.put("/{project_id}/chapters/{chapter_no}/draft")
 async def save_draft(
     project_id: uuid.UUID,