Make the offline RAG chain observable without widening credential access

Expose the verified synthetic retrieval path through a typed React client and a non-root Nginx edge while keeping database credentials and data-network reachability out of the browser tier. A fixed-origin gateway preserves request boundaries and now closes upstream streams even when downstream disconnects before body iteration. The deployment ADR and runbooks record the four-network topology and its accepted Web edge-egress risk.

Constraint: The previously exposed Bailian key must be revoked and no live provider credential may enter Git, images, logs, or the browser.
Rejected: Connect Web directly to the data network | expands lateral reach to PostgreSQL.
Rejected: Publish the database-aware API on the edge network | gives a credential-bearing process a public default route.
Rejected: Buffer streaming responses in either proxy | prevents incremental chat delivery in the future.
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Do not mark Stage 1 or Stage 2 complete until the rotated-key live smoke and remaining stage gates pass.
Tested: make verify; 65 backend tests; 14 frontend tests; Docker image build; container health and isolation probes; real HTTP demo/status/search/docs/OpenAPI checks.
Not-tested: Live Bailian models, real document ingestion, business chat SSE generation, and final browser screenshot automation because the browser skill runtime was unavailable.

docs/00-overall-design.md

@@ -132,7 +132,8 @@ deepseek-v4-flash
 ```mermaid
 flowchart LR
     U["浏览器用户"] -->|"HTTPS / SSE"| W["React + Nginx"]
-    W -->|"/api/v1"| A["FastAPI API"]
+    W -->|"同源 /api"| G["无 Secret 固定上游 Gateway"]
+    G -->|"internal data"| A["FastAPI API"]
     A --> D[("PostgreSQL + pgvector")]
     A --> F[("文件卷 / OSS 适配器")]
     A --> E["text-embedding-v4"]
@@ -150,6 +151,7 @@ flowchart LR
 | 组件 | 职责 | 不承担 |
 |---|---|---|
 | `web` | React 静态页面、Nginx 代理、SSE 透传 | 模型凭证、业务权限判断 |
+| `gateway` | 固定 API 上游、请求大小/头边界、脱敏错误和流式转发 | 数据库凭证、模型凭证、业务权限判断 |
 | `api` | 认证、知识库、检索、问答、评测 API | 长时间 OCR/批量入库 |
 | `worker` | 解析、OCR、分块、向量化、索引、评测批任务 | 对外开放端口 |
 | `db` | 元数据、向量、任务、会话、评测事实来源 | 原始大文件长期存储 |