Expose a runnable backend without giving the ingress layer secrets

The backend can now be inspected through a loopback-only gateway while the database-aware API remains on the internal data network. A governed synthetic demo proves readiness, pgvector retrieval, reranking, and citation output through real HTTP without invoking cloud models.

Constraint: The previously exposed Bailian key is compromised and cannot be used for live validation

Constraint: The API must be locally reachable while retaining no internet egress

Rejected: Attach the API directly to the ingress network | a real socket test proved that configuration still had egress

Rejected: Publish a port from the internal-only network | Docker Desktop did not expose the host port

Confidence: high

Scope-risk: moderate

Reversibility: clean

Directive: Keep model and database credentials out of the gateway; do not relax the fixed demo identity/profile filters

Tested: make verify; 63 pytest tests; strict mypy; Ruff; Secret scan; Compose config; three backend image builds; API/DB/gateway healthy; migration exit 0; Swagger browser check; live/ready/meta/status/search HTTP; 20/20/20 index; API egress ENETUNREACH; empty gateway mounts and business environment

Not-tested: Live Bailian calls require a newly rotated key; full generated-answer flow and React UI are not implemented

README.md

@@ -52,9 +52,11 @@
 make setup-hooks
 make backend-sync
 bash scripts/init-local-secrets.sh
-docker compose up -d --build db migrate
+docker compose up -d --build gateway
 docker compose --profile tools run --rm seed-demo-offline
+curl http://127.0.0.1:8000/health/ready
+curl http://127.0.0.1:8000/api/v1/demo/status
 make verify
 ```
 
-这组命令不需要百炼 Key，只使用 20 条虚构数据验证 pgvector 写入、检索、重排和幂等。真实模型运行必须先轮换聊天中已暴露的旧 Key，再按 [Stage 1 运行手册](docs/05-stage1-runbook.md) 操作。
+这组命令不需要百炼 Key，只使用 20 条虚构数据验证 pgvector 写入、检索、重排和幂等。`gateway` 会依次启动数据库、迁移和内部 API；启动后可在 <http://127.0.0.1:8000/docs> 查看 FastAPI Swagger，并通过 `POST /api/v1/demo/search` 体验只读离线检索。真实模型运行必须先轮换聊天中已暴露的旧 Key，再按 [Stage 1 运行手册](docs/05-stage1-runbook.md) 操作。