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/web/lib/api/schema.d.ts

@@ -90,6 +90,28 @@ export interface paths {
         patch?: never;
         trace?: never;
     };
+    "/projects/{project_id}/chapters/{chapter_no}/injection": {
+        parameters: {
+            query?: never;
+            header?: never;
+            path?: never;
+            cookie?: never;
+        };
+        /**
+         * Get Injection
+         * @description 本章注入透明（B0，读端点）：回放确定性 SelectionTrace。无 LLM、无 commit。
+         *
+         *     项目不存在 → 404；无大纲 → selected: []（不报错）。看到的=写章用的（不变量 #6）。
+         */
+        get: operations["get_injection_projects__project_id__chapters__chapter_no__injection_get"];
+        put?: never;
+        post?: never;
+        delete?: never;
+        options?: never;
+        head?: never;
+        patch?: never;
+        trace?: never;
+    };
     "/projects/{project_id}/chapters/{chapter_no}/draft": {
         parameters: {
             query?: never;
@@ -958,6 +980,44 @@ export interface components {
             /** Detail */
             detail?: components["schemas"]["ValidationError"][];
         };
+        /**
+         * InjectionEntity
+         * @description 一个被注入本章上下文的实体 + 入选理由（喂给透明面板的徽标）。
+         */
+        InjectionEntity: {
+            /**
+             * Kind
+             * @description character / world_entity
+             */
+            kind: string;
+            /** Name */
+            name: string;
+            /**
+             * Reasons
+             * @description explicit_beat / main_character / recent_digest / foreshadow_window
+             */
+            reasons?: string[];
+        };
+        /**
+         * InjectionResponse
+         * @description GET /projects/:id/chapters/:no/injection：本章确定性注入留痕。
+         */
+        InjectionResponse: {
+            /**
+             * Project Id
+             * Format: uuid
+             */
+            project_id: string;
+            /** Chapter No */
+            chapter_no: number;
+            /** Selected */
+            selected?: components["schemas"]["InjectionEntity"][];
+            /**
+             * Recent N
+             * @description 近况摘要回看章数（确定性选择的默认参数）
+             */
+            recent_n: number;
+        };
         /**
          * OAuthDisconnectResponse
          * @description 断开：是否删到凭据行。
@@ -1597,6 +1657,38 @@ export interface operations {
             };
         };
     };
+    get_injection_projects__project_id__chapters__chapter_no__injection_get: {
+        parameters: {
+            query?: never;
+            header?: never;
+            path: {
+                project_id: string;
+                chapter_no: number;
+            };
+            cookie?: never;
+        };
+        requestBody?: never;
+        responses: {
+            /** @description Successful Response */
+            200: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["InjectionResponse"];
+                };
+            };
+            /** @description Validation Error */
+            422: {
+                headers: {
+                    [name: string]: unknown;
+                };
+                content: {
+                    "application/json": components["schemas"]["HTTPValidationError"];
+                };
+            };
+        };
+    };
     get_draft_projects__project_id__chapters__chapter_no__draft_get: {
         parameters: {
             query?: never;

apps/web/lib/workbench/injection.test.ts

@@ -0,0 +1,27 @@
+import { describe, expect, it } from "vitest";
+
+import { kindLabel, reasonLabel } from "./injection";
+
+describe("reasonLabel", () => {
+  it("maps each known selection reason to a Chinese badge", () => {
+    expect(reasonLabel("explicit_beat")).toBe("本章点名");
+    expect(reasonLabel("main_character")).toBe("主角常驻");
+    expect(reasonLabel("recent_digest")).toBe("近章出现");
+    expect(reasonLabel("foreshadow_window")).toBe("伏笔窗口");
+  });
+
+  it("falls back to the raw code for an unknown reason", () => {
+    expect(reasonLabel("future_reason")).toBe("future_reason");
+  });
+});
+
+describe("kindLabel", () => {
+  it("maps entity kinds to Chinese", () => {
+    expect(kindLabel("character")).toBe("角色");
+    expect(kindLabel("world_entity")).toBe("设定");
+  });
+
+  it("falls back to the raw kind when unknown", () => {
+    expect(kindLabel("mystery")).toBe("mystery");
+  });
+});

apps/web/lib/workbench/injection.ts

@@ -0,0 +1,30 @@
+// 本章注入透明（B0/F1）纯逻辑：入选理由 / 实体类型 → 中文徽标。
+// 纯函数，便于 node 环境单测；渲染层只管样式。
+
+import type { components } from "@/lib/api/schema";
+
+export type InjectionResponse = components["schemas"]["InjectionResponse"];
+export type InjectionEntity = components["schemas"]["InjectionEntity"];
+
+// SelectionReason → 作者可读徽标（对齐 ARCH §3.4 的四来源）。
+export const REASON_LABELS: Record<string, string> = {
+  explicit_beat: "本章点名",
+  main_character: "主角常驻",
+  recent_digest: "近章出现",
+  foreshadow_window: "伏笔窗口",
+};
+
+// EntityKind → 中文。
+export const KIND_LABELS: Record<string, string> = {
+  character: "角色",
+  world_entity: "设定",
+};
+
+// 未知 code 时回退原值（不吞，便于发现新理由）。
+export function reasonLabel(reason: string): string {
+  return REASON_LABELS[reason] ?? reason;
+}
+
+export function kindLabel(kind: string): string {
+  return KIND_LABELS[kind] ?? kind;
+}

apps/web/lib/workbench/useInjection.ts

@@ -0,0 +1,50 @@
+"use client";
+
+import { useEffect, useState } from "react";
+
+import { api } from "@/lib/api/client";
+import type { InjectionResponse } from "./injection";
+
+export interface UseInjection {
+  data: InjectionResponse | null;
+  loading: boolean;
+  error: string | null;
+}
+
+// 本章注入透明（B0 读端点）：挂载时拉一次确定性 SelectionTrace。
+// 只读、无 LLM、无 commit——展示「选了谁/为什么」。失败给可读文案不抛。
+export function useInjection(
+  projectId: string,
+  chapterNo: number,
+): UseInjection {
+  const [data, setData] = useState<InjectionResponse | null>(null);
+  const [loading, setLoading] = useState(true);
+  const [error, setError] = useState<string | null>(null);
+
+  useEffect(() => {
+    let cancelled = false;
+    setLoading(true);
+    setError(null);
+
+    void (async () => {
+      const { data: body, error: err } = await api.GET(
+        "/projects/{project_id}/chapters/{chapter_no}/injection",
+        { params: { path: { project_id: projectId, chapter_no: chapterNo } } },
+      );
+      if (cancelled) return;
+      if (err || !body) {
+        setError("注入信息暂不可用");
+        setData(null);
+      } else {
+        setData(body);
+      }
+      setLoading(false);
+    })();
+
+    return () => {
+      cancelled = true;
+    };
+  }, [projectId, chapterNo]);
+
+  return { data, loading, error };
+}