feat(skills): Scope B A2 — 4 竞品生成器注册表+上下文分派+端点接线

注册表 TOOLBOX +4 entry（continue/expand/de-ai/teardown，全 preview-only writes=[]）；
ContextStrategy +with_prior_chapter/text_input；ToolGenerateRequest +text 字段。
toolbox_context 分派新策略（续写→build_continuation_context、原文→build_text_input_context）；
路由续写经 chapter_repo 读最新 accepted/draft 正文注入 builder（core 不 import apps/api，仿 accept_op）。
预览仅 commit ledger 不写业务表（#3）；只声明 tier（#2）；system_prompt 进缓存前缀（#9）。
单测：4 生成器 generate 预览 + 续写读前文/草稿路由 + 扩写/降AI text 路由 + 拆书结构化；
更新 registry/strategy 计数测试（15 工具 / 6 策略）。门禁绿：ruff/format/mypy 196 files/pytest 168(api)+32(skills)。

apps/api/ww_api/routers/toolbox.py

@@ -20,6 +20,7 @@ from typing import Annotated, Any
 from fastapi import APIRouter, Depends, Request
 from sqlalchemy.ext.asyncio import AsyncSession
 from ww_agents import AgentSpec, Conflict, ContinuityReview, continuity_spec
+from ww_core.domain.chapter_repo import ChapterRepo
 from ww_core.domain.outline_write_repo import OutlineWriteRepo
 from ww_core.domain.project_repo import ProjectRepo
 from ww_core.domain.repositories import MemoryRepos, OutlineRepo
@@ -47,6 +48,7 @@ from ww_api.schemas.toolbox import (
 from ww_api.services.credentials import STUB_OWNER_ID
 from ww_api.services.project_deps import (
     TierGatewayBuilder,
+    get_chapter_repo,
     get_memory_repos,
     get_outline_read_repo,
     get_outline_write_repo,
@@ -74,6 +76,7 @@ _INGEST_ERRORS: dict[int | str, dict[str, Any]] = {
 ProjectRepoDep = Annotated[ProjectRepo, Depends(get_project_repo)]
 MemoryReposDep = Annotated[MemoryRepos, Depends(get_memory_repos)]
 OutlineReadRepoDep = Annotated[OutlineRepo, Depends(get_outline_read_repo)]
+ChapterRepoDep = Annotated[ChapterRepo, Depends(get_chapter_repo)]
 WorldWriteRepoDep = Annotated[WorldEntityWriteRepo, Depends(get_world_entity_write_repo)]
 OutlineWriteRepoDep = Annotated[OutlineWriteRepo, Depends(get_outline_write_repo)]
 GatewayBuilderDep = Annotated[TierGatewayBuilder, Depends(get_tier_gateway_builder)]
@@ -138,6 +141,23 @@ async def _chapter_beats(
     return list(raw.get("beats", [])) if isinstance(raw, dict) else []
 
 
+async def _prior_chapter_text(
+    chapter_repo: ChapterRepo, project_id: uuid.UUID, chapter_no: int
+) -> str:
+    """读续写承接的前文正文：优先该章最新 accepted，无则草稿，皆无 → 空串（端点降级）。
+
+    core 的 builder 不 import apps/api——正文在端点读 chapter 领域表后经参数注入
+    （仿链 accept_op 的注入模式），守不变量 #1（DB 为真相源）。
+    """
+    accepted = await chapter_repo.latest_accepted(project_id, chapter_no)
+    if accepted is not None and accepted.content.strip():
+        return accepted.content
+    draft = await chapter_repo.get_draft(project_id, chapter_no)
+    if draft is not None and draft.content.strip():
+        return draft.content
+    return ""
+
+
 @router.post("/projects/{project_id}/skills/{tool_key}/generate", responses=_TOOL_ERRORS)
 async def generate_with_tool(
     project_id: uuid.UUID,
@@ -147,6 +167,7 @@ async def generate_with_tool(
     project_repo: ProjectRepoDep,
     memory: MemoryReposDep,
     outline_repo: OutlineReadRepoDep,
+    chapter_repo: ChapterRepoDep,
     build_gateway: GatewayBuilderDep,
     session: SessionDep,
 ) -> ToolGeneratePreviewResponse:
@@ -170,11 +191,17 @@ async def generate_with_tool(
 
     world_context = ""
     beats: list[str] = []
+    prior_text = ""
     if tool.context_strategy == "with_world":
         world_context = await _world_context(memory, project_id)
     elif tool.context_strategy == "with_outline_chapter":
         chapter_no = body.chapter_no or 1
         beats = await _chapter_beats(outline_repo, project_id, chapter_no)
+    elif tool.context_strategy == "with_prior_chapter":
+        # 续写：端点先读该章最新 accepted/draft 正文（DB 为真相源，#1）+ 该章节拍，注入 builder。
+        chapter_no = body.chapter_no or 1
+        prior_text = await _prior_chapter_text(chapter_repo, project_id, chapter_no)
+        beats = await _chapter_beats(outline_repo, project_id, chapter_no)
 
     context = build_toolbox_context(
         tool.context_strategy,
@@ -183,6 +210,8 @@ async def generate_with_tool(
         world_context=world_context,
         chapter_no=body.chapter_no,
         beats=beats,
+        prior_text=prior_text,
+        text=body.text or "",
     )
 
     gateway = await build_gateway(spec.tier)