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

backend/Dockerfile

@@ -24,10 +24,9 @@ COPY migrations ./migrations
 COPY app ./app
 COPY README.md ./
 
-RUN uv sync --frozen --no-dev \
-    && chown -R app:app /app
+RUN uv sync --frozen --no-dev
 
-USER app
+USER 10001:10001
 EXPOSE 8000
 
-CMD ["python", "-m", "app.main"]
+CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]