feat(ux): B0 注入透明读端点 + F1 写作页右栏真面板

兑现「看到的=写章用的」信任牌（不变量 #6），替换写作页右栏过时假占位
（「M1 暂未接 / M2 开放」）。

后端：
- GET /projects/{id}/chapters/{no}/injection → InjectionResponse（selected
  实体 + 入选理由 + recent_n）；调既有 assemble() 回放确定性 SelectionTrace，
  无 LLM / 无 commit / 无 DDL；项目不存在→404，无大纲→selected:[]。
- 新 schemas/injection.py；tests/test_injection.py(3 测)。

前端：
- gen:api 纳入端点；纯逻辑 lib/workbench/injection.ts（理由/类型→中文徽标
  + 4 vitest）+ useInjection 读 hook。
- ChapterAssistant 改 client 组件：列出选中实体 + 理由徽标 + 空/载/错三态，
  四审段指向审稿页；Workbench 传 projectId/chapterNo。

门禁：后端 ruff/format/mypy 159/alembic 无漂移/pytest 454；
前端 lint/typecheck/vitest 167/build。

B0 可控版（PUT override pin/排除/recent_n + selection 加参 + draft 同读
override + 持久化）+ F1 可控控件待后续。

apps/api/tests/test_injection.py

@@ -0,0 +1,169 @@
+"""B0 注入透明读端点测试：GET /projects/:id/chapters/:no/injection。
+
+读取 assemble 的确定性 SelectionTrace（无 LLM、无 commit）：
+- 命中实体 + 入选理由徽标；项目不存在 → 404；无大纲 → selected: []（不报错）。
+"""
+
+from __future__ import annotations
+
+import uuid
+
+import httpx
+import pytest
+from fakes_projects import FakeProjectRepo
+from ww_api.services.credentials import STUB_OWNER_ID
+from ww_core.domain.project_repo import ProjectCreate
+from ww_core.domain.repositories import (
+    CharacterView,
+    DigestView,
+    ForeshadowView,
+    MemoryRepos,
+    OutlineView,
+    ProjectSpecView,
+    RuleView,
+    StyleView,
+    WorldEntityView,
+)
+from ww_shared import ErrorCode
+
+# ---- 内存 fake memory repos（无 DB；只够断言 SelectionTrace 形状）----
+
+
+class _OutlineRepo:
+    def __init__(self, rows: dict[int, OutlineView]) -> None:
+        self._rows = rows
+
+    async def get(self, project_id: uuid.UUID, chapter_no: int) -> OutlineView | None:
+        return self._rows.get(chapter_no)
+
+    async def list_for_project(self, project_id: uuid.UUID) -> list[OutlineView]:
+        return [self._rows[k] for k in sorted(self._rows)]
+
+
+class _CharRepo:
+    def __init__(self, rows: list[CharacterView]) -> None:
+        self._rows = rows
+
+    async def list_for_project(self, project_id: uuid.UUID) -> list[CharacterView]:
+        return list(self._rows)
+
+
+class _WorldRepo:
+    def __init__(self, rows: list[WorldEntityView]) -> None:
+        self._rows = rows
+
+    async def list_for_project(self, project_id: uuid.UUID) -> list[WorldEntityView]:
+        return list(self._rows)
+
+
+class _DigestRepo:
+    async def recent(self, project_id: uuid.UUID, k: int) -> list[DigestView]:
+        return []
+
+
+class _ForeshadowRepo:
+    async def list_for_codes(self, project_id: uuid.UUID, codes: list[str]) -> list[ForeshadowView]:
+        return []
+
+
+class _StyleRepo:
+    async def latest(self, project_id: uuid.UUID) -> StyleView | None:
+        return None
+
+
+class _RulesRepo:
+    async def all_for_project(self, project_id: uuid.UUID) -> list[RuleView]:
+        return []
+
+
+class _SpecRepo:
+    async def spec(self, project_id: uuid.UUID) -> ProjectSpecView | None:
+        return ProjectSpecView(title="测试作品", premise="测试前提")
+
+
+def _memory_repos(
+    *,
+    outline: dict[int, OutlineView] | None = None,
+    characters: list[CharacterView] | None = None,
+    world: list[WorldEntityView] | None = None,
+) -> MemoryRepos:
+    return MemoryRepos(
+        outline=_OutlineRepo(outline or {}),
+        character=_CharRepo(characters or []),
+        world_entity=_WorldRepo(world or []),
+        digest=_DigestRepo(),
+        foreshadow=_ForeshadowRepo(),
+        style=_StyleRepo(),
+        rules=_RulesRepo(),
+        project=_SpecRepo(),
+    )
+
+
+def _make_client(
+    *,
+    project_repo: FakeProjectRepo,
+    memory_repos: MemoryRepos,
+) -> httpx.AsyncClient:
+    import os
+
+    os.environ.setdefault("CREDENTIAL_ENC_KEY", "x" * 44)
+    from ww_api.main import create_app
+    from ww_api.services.project_deps import get_memory_repos, get_project_repo
+
+    app = create_app()
+    app.dependency_overrides[get_project_repo] = lambda: project_repo
+    app.dependency_overrides[get_memory_repos] = lambda: memory_repos
+    transport = httpx.ASGITransport(app=app)
+    return httpx.AsyncClient(transport=transport, base_url="http://test")
+
+
+async def _create_project(repo: FakeProjectRepo, title: str = "注入") -> uuid.UUID:
+    view = await repo.create(STUB_OWNER_ID, ProjectCreate(title=title))
+    return uuid.UUID(str(view.id))
+
+
+@pytest.mark.asyncio
+async def test_injection_lists_selected_entities_with_reasons() -> None:
+    repo = FakeProjectRepo()
+    pid = await _create_project(repo)
+    memory = _memory_repos(
+        outline={3: OutlineView(volume=1, chapter_no=3, beats={"entities": ["青檀"]})},
+        characters=[
+            CharacterView(name="林动", role="主角"),
+            CharacterView(name="青檀", role="配角"),
+            CharacterView(name="路人甲", role="龙套"),
+        ],
+    )
+    client = _make_client(project_repo=repo, memory_repos=memory)
+    async with client:
+        resp = await client.get(f"/projects/{pid}/chapters/3/injection")
+    assert resp.status_code == 200
+    body = resp.json()
+    assert body["project_id"] == str(pid)
+    assert body["chapter_no"] == 3
+    by_name = {e["name"]: e for e in body["selected"]}
+    assert "林动" in by_name and "main_character" in by_name["林动"]["reasons"]
+    assert "青檀" in by_name and "explicit_beat" in by_name["青檀"]["reasons"]
+    assert "路人甲" not in by_name  # 未命中任何理由 → 不注入
+    assert body["recent_n"] >= 1
+
+
+@pytest.mark.asyncio
+async def test_injection_unknown_project_404() -> None:
+    repo = FakeProjectRepo()
+    client = _make_client(project_repo=repo, memory_repos=_memory_repos())
+    async with client:
+        resp = await client.get(f"/projects/{uuid.uuid4()}/chapters/1/injection")
+    assert resp.status_code == 404
+    assert resp.json()["error"]["code"] == ErrorCode.NOT_FOUND
+
+
+@pytest.mark.asyncio
+async def test_injection_no_outline_returns_empty() -> None:
+    repo = FakeProjectRepo()
+    pid = await _create_project(repo)
+    client = _make_client(project_repo=repo, memory_repos=_memory_repos())
+    async with client:
+        resp = await client.get(f"/projects/{pid}/chapters/9/injection")
+    assert resp.status_code == 200
+    assert resp.json()["selected"] == []