feat(b0): 注入透明可控版后端 — PUT override(pin/排除/recent_n) + 选择函数加参 + draft 同读

- selection.select_relevant_entities 加 pinned/excluded frozenset 入参；新理由 author_pin（末位）
- assemble 加 override 关键字参（recent_n 覆盖回看章数 + pin/排除）；GET/PUT/draft 同读同一覆盖（不变量 #6 作者兜底）
- 新 domain/injection_repo.py（InjectionOverride/EntityRef/SqlInjectionOverrideRepo，upsert 只 flush）
- 新表 chapter_injection（迁移 ad2c4c663daf，唯一 project_id+chapter_no；复用 outline 行已否决）
- PUT/GET injection 端点 + InjectionOverrideRequest/回显 pinned/excluded；recent_n 1..20 校验 422
- 单测：selection pin/排除/exclude>pin + assemble override + 端点 PUT/404/422；regen TS 客户端
- 门禁绿：ruff/format · mypy 163 · alembic 无漂移 · pytest 476

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

apps/api/tests/test_injection.py

@@ -12,6 +12,7 @@ import httpx
 import pytest
 from fakes_projects import FakeProjectRepo
 from ww_api.services.credentials import STUB_OWNER_ID
+from ww_core.domain.injection_repo import InjectionOverride
 from ww_core.domain.project_repo import ProjectCreate
 from ww_core.domain.repositories import (
     CharacterView,
@@ -81,6 +82,22 @@ class _SpecRepo:
         return ProjectSpecView(title="测试作品", premise="测试前提")
 
 
+class _FakeInjectionRepo:
+    """内存注入覆盖 repo（按 (project_id, chapter_no) 存最后一次 upsert）。"""
+
+    def __init__(self) -> None:
+        self._store: dict[tuple[str, int], InjectionOverride] = {}
+
+    async def get(self, project_id: uuid.UUID, chapter_no: int) -> InjectionOverride | None:
+        return self._store.get((str(project_id), chapter_no))
+
+    async def upsert(
+        self, project_id: uuid.UUID, chapter_no: int, override: InjectionOverride
+    ) -> InjectionOverride:
+        self._store[(str(project_id), chapter_no)] = override
+        return override
+
+
 def _memory_repos(
     *,
     outline: dict[int, OutlineView] | None = None,
@@ -103,16 +120,25 @@ def _make_client(
     *,
     project_repo: FakeProjectRepo,
     memory_repos: MemoryRepos,
+    injection_repo: _FakeInjectionRepo | None = None,
 ) -> httpx.AsyncClient:
     import os
 
     os.environ.setdefault("CREDENTIAL_ENC_KEY", "x" * 44)
+    from fakes_projects import FakeSession
     from ww_api.main import create_app
-    from ww_api.services.project_deps import get_memory_repos, get_project_repo
+    from ww_api.services.project_deps import (
+        get_injection_repo,
+        get_memory_repos,
+        get_project_repo,
+    )
+    from ww_db import get_session
 
     app = create_app()
     app.dependency_overrides[get_project_repo] = lambda: project_repo
     app.dependency_overrides[get_memory_repos] = lambda: memory_repos
+    app.dependency_overrides[get_injection_repo] = lambda: injection_repo or _FakeInjectionRepo()
+    app.dependency_overrides[get_session] = lambda: FakeSession()
     transport = httpx.ASGITransport(app=app)
     return httpx.AsyncClient(transport=transport, base_url="http://test")
 
@@ -167,3 +193,68 @@ async def test_injection_no_outline_returns_empty() -> None:
         resp = await client.get(f"/projects/{pid}/chapters/9/injection")
     assert resp.status_code == 200
     assert resp.json()["selected"] == []
+
+
+@pytest.mark.asyncio
+async def test_injection_put_pin_excludes_and_reflects() -> None:
+    repo = FakeProjectRepo()
+    pid = await _create_project(repo)
+    memory = _memory_repos(
+        outline={3: OutlineView(volume=1, chapter_no=3, beats={})},
+        characters=[
+            CharacterView(name="林动", role="主角"),
+            CharacterView(name="路人乙", role="龙套"),
+        ],
+    )
+    injection = _FakeInjectionRepo()
+    client = _make_client(project_repo=repo, memory_repos=memory, injection_repo=injection)
+    async with client:
+        # pin 龙套路人乙（本无理由）、排除主角林动、近况回看设为 2。
+        put = await client.put(
+            f"/projects/{pid}/chapters/3/injection",
+            json={
+                "pinned": [{"kind": "character", "name": "路人乙"}],
+                "excluded": [{"kind": "character", "name": "林动"}],
+                "recent_n": 2,
+            },
+        )
+        assert put.status_code == 200
+        body = put.json()
+        by_name = {e["name"]: e for e in body["selected"]}
+        assert "路人乙" in by_name and "author_pin" in by_name["路人乙"]["reasons"]
+        assert "林动" not in by_name  # 排除生效
+        assert body["recent_n"] == 2
+        assert body["pinned"] == [{"kind": "character", "name": "路人乙"}]
+        assert body["excluded"] == [{"kind": "character", "name": "林动"}]
+
+        # 覆盖已落 fake repo → GET 回放同一结果（看到的=写章用的）。
+        got = await client.get(f"/projects/{pid}/chapters/3/injection")
+        assert got.status_code == 200
+        got_names = {e["name"] for e in got.json()["selected"]}
+        assert "路人乙" in got_names and "林动" not in got_names
+
+
+@pytest.mark.asyncio
+async def test_injection_put_unknown_project_404() -> None:
+    repo = FakeProjectRepo()
+    client = _make_client(project_repo=repo, memory_repos=_memory_repos())
+    async with client:
+        resp = await client.put(
+            f"/projects/{uuid.uuid4()}/chapters/1/injection",
+            json={"pinned": [], "excluded": [], "recent_n": None},
+        )
+    assert resp.status_code == 404
+    assert resp.json()["error"]["code"] == ErrorCode.NOT_FOUND
+
+
+@pytest.mark.asyncio
+async def test_injection_put_rejects_out_of_range_recent_n() -> None:
+    repo = FakeProjectRepo()
+    pid = await _create_project(repo)
+    client = _make_client(project_repo=repo, memory_repos=_memory_repos())
+    async with client:
+        resp = await client.put(
+            f"/projects/{pid}/chapters/1/injection",
+            json={"pinned": [], "excluded": [], "recent_n": 999},
+        )
+    assert resp.status_code == 422