diff --git a/README.md b/README.md
index 2d1bf34..47b6c99 100644
--- a/README.md
+++ b/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。
diff --git a/backend/Dockerfile b/backend/Dockerfile
index c3e017e..81f40fe 100644
--- a/backend/Dockerfile
+++ b/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"]
diff --git a/backend/app/api/__init__.py b/backend/app/api/__init__.py
new file mode 100644
index 0000000..bfd61f4
--- /dev/null
+++ b/backend/app/api/__init__.py
@@ -0,0 +1 @@
+"""HTTP API routers for the geological RAG backend."""
diff --git a/backend/app/api/v1/__init__.py b/backend/app/api/v1/__init__.py
new file mode 100644
index 0000000..2eb88ef
--- /dev/null
+++ b/backend/app/api/v1/__init__.py
@@ -0,0 +1,5 @@
+"""Version 1 HTTP API routers."""
+
+from app.api.v1.demo import router as demo_router
+
+__all__ = ["demo_router"]
diff --git a/backend/app/api/v1/demo.py b/backend/app/api/v1/demo.py
new file mode 100644
index 0000000..3f50be4
--- /dev/null
+++ b/backend/app/api/v1/demo.py
@@ -0,0 +1,356 @@
+"""Read-only offline RAG demo endpoints backed by the synthetic dataset."""
+
+from __future__ import annotations
+
+import asyncio
+import hashlib
+import re
+from dataclasses import dataclass
+from typing import Annotated, Any, Literal, Protocol, cast
+
+import psycopg
+from fastapi import APIRouter, Depends, HTTPException, status
+from pgvector.psycopg import register_vector
+from pgvector.vector import Vector
+from psycopg.rows import dict_row
+from pydantic import BaseModel, Field, field_validator
+
+from app.adapters.fake import FakeEmbeddingProvider, FakeReranker
+from app.core.config import Settings, get_settings
+from app.core.demo_identity import (
+    ACCESS_SCOPE_ID,
+    DEMO_EXPECTED_CHUNKS,
+    DEMO_FAKE_EMBEDDING_MODEL,
+    DEMO_SCOPE_NAME,
+    KNOWLEDGE_BASE_ID,
+    offline_embedding_profile_hash,
+)
+from app.core.secrets import SecretFileError
+
+QUERY_MAX_LENGTH = 500
+SNIPPET_MAX_LENGTH = 600
+TITLE_MAX_LENGTH = 120
+_SPACE_PATTERN = re.compile(r"\s+")
+
+
+class DemoCounts(BaseModel):
+    """Public aggregate counts for the synthetic dataset."""
+
+    chunks: int = Field(ge=0)
+    vectors: int = Field(ge=0)
+    searchable: int = Field(ge=0)
+
+
+class DemoStatusResponse(BaseModel):
+    """Safe readiness summary without database or approval internals."""
+
+    status: Literal["ready", "empty_dataset", "incomplete_dataset"]
+    dataset: Literal["synthetic-demo"] = "synthetic-demo"
+    counts: DemoCounts
+
+
+class DemoSearchRequest(BaseModel):
+    """Bounded request accepted by the offline demo search."""
+
+    query: str = Field(min_length=1, max_length=QUERY_MAX_LENGTH)
+    top_k: int = Field(default=5, ge=1, le=10)
+
+    @field_validator("query")
+    @classmethod
+    def normalize_query(cls, value: str) -> str:
+        normalized = _SPACE_PATTERN.sub(" ", value).strip()
+        if not normalized:
+            raise ValueError("query must contain non-whitespace text")
+        return normalized
+
+
+class DemoSearchItem(BaseModel):
+    """Public synthetic result; internal identifiers and hashes are excluded."""
+
+    title: str
+    snippet: str
+    page_label: str
+    score: float = Field(ge=0.0, le=1.0)
+    citation_id: str
+
+
+class DemoSearchResponse(BaseModel):
+    """Offline retrieval response with an explicit empty-dataset state."""
+
+    status: Literal["ok", "empty_dataset"]
+    dataset: Literal["synthetic-demo"] = "synthetic-demo"
+    results: list[DemoSearchItem]
+
+
+@dataclass(frozen=True, slots=True)
+class DemoCandidate:
+    """Private retrieval projection used only while constructing safe results."""
+
+    source_key: str
+    title: str
+    text: str
+    page_start: int | None
+    page_end: int | None
+
+    @property
+    def rerank_text(self) -> str:
+        return f"{self.title}\n{self.text}"
+
+
+class DemoRepository(Protocol):
+    """Read-only persistence boundary used by the demo router."""
+
+    def counts(self) -> DemoCounts: ...
+
+    def search(self, query_vector: tuple[float, ...], *, limit: int) -> list[DemoCandidate]: ...
+
+
+class PostgresDemoRepository:
+    """Read-only PostgreSQL/pgvector projection for approved synthetic chunks."""
+
+    def __init__(self, settings: Settings) -> None:
+        self._settings = settings
+
+    def _dsn(self) -> str:
+        return (
+            self._settings.database_url()
+            .set(drivername="postgresql")
+            .render_as_string(hide_password=False)
+        )
+
+    def counts(self) -> DemoCounts:
+        profile_hash = offline_embedding_profile_hash(self._settings.embedding_dimension)
+        with psycopg.connect(
+            self._dsn(),
+            connect_timeout=2,
+            row_factory=dict_row,
+        ) as connection:
+            row = connection.execute(
+                """
+                SELECT
+                  count(*)::integer AS chunks,
+                  count(*) FILTER (WHERE chunk.embedding IS NOT NULL)::integer AS vectors,
+                  count(*) FILTER (WHERE chunk.searchable)::integer AS searchable
+                FROM rag.chunks AS chunk
+                JOIN rag.access_scopes AS scope
+                  ON scope.id = chunk.access_scope_id
+                 AND scope.knowledge_base_id = chunk.knowledge_base_id
+                JOIN rag.documents AS document
+                  ON document.id = chunk.document_id
+                 AND document.knowledge_base_id = chunk.knowledge_base_id
+                 AND document.access_scope_id = chunk.access_scope_id
+                JOIN rag.document_versions AS version
+                  ON version.id = chunk.document_version_id
+                 AND version.document_id = chunk.document_id
+                WHERE chunk.knowledge_base_id = %s
+                  AND chunk.access_scope_id = %s
+                  AND scope.name = %s
+                  AND chunk.metadata ->> 'source_type' = 'synthetic'
+                  AND chunk.index_status = 'READY'
+                  AND chunk.approval_status = 'CLOUD_APPROVED'
+                  AND chunk.deleted_at IS NULL
+                  AND chunk.embedding_model = %s
+                  AND chunk.embedding_profile_hash = %s
+                  AND document.status = 'READY'
+                  AND document.deleted_at IS NULL
+                  AND document.active_version_id = chunk.document_version_id
+                  AND version.status = 'READY'
+                  AND version.review_state = 'CLOUD_APPROVED'
+                  AND version.outbound_manifest_sha256 = chunk.outbound_manifest_sha256
+                  AND version.embedding_profile_hash = chunk.embedding_profile_hash
+                """,
+                (
+                    KNOWLEDGE_BASE_ID,
+                    ACCESS_SCOPE_ID,
+                    DEMO_SCOPE_NAME,
+                    DEMO_FAKE_EMBEDDING_MODEL,
+                    profile_hash,
+                ),
+            ).fetchone()
+        if row is None:
+            return DemoCounts(chunks=0, vectors=0, searchable=0)
+        return DemoCounts(
+            chunks=int(row["chunks"]),
+            vectors=int(row["vectors"]),
+            searchable=int(row["searchable"]),
+        )
+
+    def search(self, query_vector: tuple[float, ...], *, limit: int) -> list[DemoCandidate]:
+        if len(query_vector) != self._settings.embedding_dimension:
+            raise ValueError("query vector dimension does not match the demo index")
+
+        vector = Vector(list(query_vector))
+        profile_hash = offline_embedding_profile_hash(self._settings.embedding_dimension)
+        with psycopg.connect(
+            self._dsn(),
+            connect_timeout=2,
+            row_factory=dict_row,
+        ) as connection:
+            register_vector(connection)
+            connection.execute("SET LOCAL statement_timeout = '3000ms'")
+            connection.execute("SET LOCAL hnsw.iterative_scan = strict_order")
+            connection.execute("SET LOCAL hnsw.ef_search = 100")
+            rows = connection.execute(
+                """
+                SELECT
+                  chunk.id::text AS source_key,
+                  COALESCE(NULLIF(chunk.section_path ->> 0, ''), '合成地质资料') AS title,
+                  chunk.cloud_text AS text,
+                  chunk.page_start,
+                  chunk.page_end
+                FROM rag.chunks AS chunk
+                JOIN rag.access_scopes AS scope
+                  ON scope.id = chunk.access_scope_id
+                 AND scope.knowledge_base_id = chunk.knowledge_base_id
+                JOIN rag.documents AS document
+                  ON document.id = chunk.document_id
+                 AND document.knowledge_base_id = chunk.knowledge_base_id
+                 AND document.access_scope_id = chunk.access_scope_id
+                JOIN rag.document_versions AS version
+                  ON version.id = chunk.document_version_id
+                 AND version.document_id = chunk.document_id
+                WHERE chunk.knowledge_base_id = %s
+                  AND chunk.access_scope_id = %s
+                  AND scope.name = %s
+                  AND chunk.metadata ->> 'source_type' = 'synthetic'
+                  AND chunk.searchable IS TRUE
+                  AND chunk.embedding IS NOT NULL
+                  AND chunk.index_status = 'READY'
+                  AND chunk.approval_status = 'CLOUD_APPROVED'
+                  AND chunk.deleted_at IS NULL
+                  AND chunk.embedding_model = %s
+                  AND chunk.embedding_profile_hash = %s
+                  AND document.status = 'READY'
+                  AND document.deleted_at IS NULL
+                  AND document.active_version_id = chunk.document_version_id
+                  AND version.status = 'READY'
+                  AND version.review_state = 'CLOUD_APPROVED'
+                  AND version.outbound_manifest_sha256 = chunk.outbound_manifest_sha256
+                  AND version.embedding_profile_hash = chunk.embedding_profile_hash
+                ORDER BY chunk.embedding <=> %s
+                LIMIT %s
+                """,
+                (
+                    KNOWLEDGE_BASE_ID,
+                    ACCESS_SCOPE_ID,
+                    DEMO_SCOPE_NAME,
+                    DEMO_FAKE_EMBEDDING_MODEL,
+                    profile_hash,
+                    vector,
+                    limit,
+                ),
+            ).fetchall()
+
+        return [
+            DemoCandidate(
+                source_key=cast(str, row["source_key"]),
+                title=cast(str, row["title"]),
+                text=cast(str, row["text"]),
+                page_start=cast(int | None, row["page_start"]),
+                page_end=cast(int | None, row["page_end"]),
+            )
+            for row in rows
+        ]
+
+
+def get_demo_repository(
+    settings: Annotated[Settings, Depends(get_settings)],
+) -> DemoRepository:
+    """Build the default repository without loading any model credential."""
+
+    return PostgresDemoRepository(settings)
+
+
+def _bounded_text(value: str, max_length: int) -> str:
+    normalized = _SPACE_PATTERN.sub(" ", value).strip()
+    if len(normalized) <= max_length:
+        return normalized
+    return f"{normalized[: max_length - 1]}…"
+
+
+def make_citation_id(source_key: str) -> str:
+    """Derive a stable opaque citation without returning an internal UUID."""
+
+    digest = hashlib.sha256(f"{DEMO_SCOPE_NAME}:{source_key}".encode()).hexdigest()
+    return f"demo-{digest[:16]}"
+
+
+def make_page_label(page_start: int | None, page_end: int | None) -> str:
+    if page_start is None or page_end is None:
+        return "页码未知"
+    if page_start == page_end:
+        return f"第 {page_start} 页"
+    return f"第 {page_start}-{page_end} 页"
+
+
+def _safe_result(candidate: DemoCandidate, score: float) -> DemoSearchItem:
+    return DemoSearchItem(
+        title=f"合成资料｜{_bounded_text(candidate.title, TITLE_MAX_LENGTH)}",
+        snippet=_bounded_text(candidate.text, SNIPPET_MAX_LENGTH),
+        page_label=make_page_label(candidate.page_start, candidate.page_end),
+        score=round(max(0.0, min(1.0, score)), 6),
+        citation_id=make_citation_id(candidate.source_key),
+    )
+
+
+def _database_unavailable(exc: BaseException) -> HTTPException:
+    return HTTPException(
+        status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
+        detail="database unavailable",
+    )
+
+
+router = APIRouter(prefix="/api/v1/demo", tags=["offline-demo"])
+
+
+@router.get("/status", response_model=DemoStatusResponse)
+def demo_status(repository: Annotated[DemoRepository, Depends(get_demo_repository)]) -> Any:
+    try:
+        counts = repository.counts()
+    except (OSError, SecretFileError, psycopg.Error) as exc:
+        raise _database_unavailable(exc) from exc
+    state: Literal["ready", "empty_dataset", "incomplete_dataset"]
+    if counts.chunks == 0:
+        state = "empty_dataset"
+    elif (
+        counts.chunks == DEMO_EXPECTED_CHUNKS
+        and counts.vectors == DEMO_EXPECTED_CHUNKS
+        and counts.searchable == DEMO_EXPECTED_CHUNKS
+    ):
+        state = "ready"
+    else:
+        state = "incomplete_dataset"
+    return DemoStatusResponse(status=state, counts=counts)
+
+
+@router.post("/search", response_model=DemoSearchResponse)
+async def demo_search(
+    request: DemoSearchRequest,
+    repository: Annotated[DemoRepository, Depends(get_demo_repository)],
+    settings: Annotated[Settings, Depends(get_settings)],
+) -> Any:
+    embedder = FakeEmbeddingProvider(settings.embedding_dimension)
+    reranker = FakeReranker()
+    query_result = await embedder.embed_query(request.query)
+    candidate_limit = min(max(request.top_k * 3, 10), 20)
+    try:
+        candidates = await asyncio.to_thread(
+            repository.search,
+            query_result.vectors[0],
+            limit=candidate_limit,
+        )
+    except (OSError, SecretFileError, psycopg.Error) as exc:
+        raise _database_unavailable(exc) from exc
+
+    if not candidates:
+        return DemoSearchResponse(status="empty_dataset", results=[])
+
+    reranked = await reranker.rerank(
+        request.query,
+        [candidate.rerank_text for candidate in candidates],
+        top_n=min(request.top_k, len(candidates)),
+    )
+    results = [
+        _safe_result(candidates[item.index], item.relevance_score) for item in reranked.items
+    ]
+    return DemoSearchResponse(status="ok", results=results)
diff --git a/backend/app/core/demo_identity.py b/backend/app/core/demo_identity.py
new file mode 100644
index 0000000..f408406
--- /dev/null
+++ b/backend/app/core/demo_identity.py
@@ -0,0 +1,35 @@
+"""Stable identity and embedding profile for the public synthetic demo corpus."""
+
+from __future__ import annotations
+
+import hashlib
+import json
+import uuid
+
+DEMO_SCOPE_NAME = "synthetic-demo"
+DEMO_EXPECTED_CHUNKS = 20
+DEMO_FAKE_EMBEDDING_MODEL = "fake-feature-hash-v1"
+
+IDENTITY_NAMESPACE = uuid.UUID("eef85571-1f64-4a09-86d7-53fd329c3eb2")
+KNOWLEDGE_BASE_ID = uuid.uuid5(IDENTITY_NAMESPACE, "synthetic-demo-knowledge-base")
+ACCESS_SCOPE_ID = uuid.uuid5(IDENTITY_NAMESPACE, "synthetic-demo-public-scope")
+
+
+def offline_embedding_profile_hash(dimension: int) -> str:
+    """Return the exact profile bound to vectors produced by the offline embedder."""
+
+    profile = {
+        "api_mode": "deterministic-offline",
+        "dimension": dimension,
+        "endpoint_identity_hash": "local-fake",
+        "model": DEMO_FAKE_EMBEDDING_MODEL,
+        "normalization": "provider-default",
+        "profile_version": 1,
+    }
+    serialized = json.dumps(
+        profile,
+        ensure_ascii=False,
+        sort_keys=True,
+        separators=(",", ":"),
+    )
+    return hashlib.sha256(serialized.encode("utf-8")).hexdigest()
diff --git a/backend/app/gateway.py b/backend/app/gateway.py
new file mode 100644
index 0000000..a100d3f
--- /dev/null
+++ b/backend/app/gateway.py
@@ -0,0 +1,161 @@
+"""Small fixed-origin ingress gateway with explicit proxy boundaries."""
+
+from collections.abc import AsyncIterator, Mapping
+from contextlib import asynccontextmanager
+
+import httpx
+from fastapi import FastAPI, Request, Response, status
+from fastapi.responses import JSONResponse
+
+UPSTREAM_ORIGIN = httpx.URL("http://api:8000")
+MAX_REQUEST_BODY_BYTES = 1024 * 1024
+SUPPORTED_METHODS = ["GET", "POST", "HEAD", "OPTIONS"]
+
+REQUEST_HEADER_ALLOWLIST = frozenset(
+    {
+        "accept",
+        "accept-language",
+        "access-control-request-headers",
+        "access-control-request-method",
+        "authorization",
+        "content-type",
+        "if-match",
+        "if-none-match",
+        "origin",
+        "range",
+        "traceparent",
+        "tracestate",
+        "x-request-id",
+    }
+)
+
+RESPONSE_HEADER_ALLOWLIST = frozenset(
+    {
+        "accept-ranges",
+        "access-control-allow-credentials",
+        "access-control-allow-headers",
+        "access-control-allow-methods",
+        "access-control-allow-origin",
+        "access-control-max-age",
+        "allow",
+        "cache-control",
+        "content-disposition",
+        "content-language",
+        "content-range",
+        "content-type",
+        "etag",
+        "last-modified",
+        "retry-after",
+        "vary",
+        "www-authenticate",
+        "x-request-id",
+    }
+)
+
+
+def _allowlisted_headers(headers: Mapping[str, str], allowlist: frozenset[str]) -> dict[str, str]:
+    return {name: value for name, value in headers.items() if name.lower() in allowlist}
+
+
+def _upstream_url(request: Request) -> httpx.URL:
+    raw_path_value: object = request.scope.get("raw_path")
+    if isinstance(raw_path_value, bytes):
+        raw_path = raw_path_value
+    else:
+        raw_path = request.url.path.encode("utf-8")
+    if not raw_path.startswith(b"/"):
+        raw_path = b"/" + raw_path
+
+    query_value: object = request.scope.get("query_string")
+    query = query_value if isinstance(query_value, bytes) else b""
+    raw_target = raw_path + (b"?" + query if query else b"")
+    # copy_with preserves the fixed scheme, host, and port even for //host-like paths.
+    return UPSTREAM_ORIGIN.copy_with(raw_path=raw_target)
+
+
+async def _bounded_body(request: Request) -> bytes | None:
+    declared_length = request.headers.get("content-length")
+    if declared_length is not None:
+        try:
+            parsed_length = int(declared_length)
+        except ValueError:
+            return None
+        if parsed_length < 0 or parsed_length > MAX_REQUEST_BODY_BYTES:
+            return None
+
+    body = bytearray()
+    async for chunk in request.stream():
+        if len(body) + len(chunk) > MAX_REQUEST_BODY_BYTES:
+            return None
+        body.extend(chunk)
+    return bytes(body)
+
+
+def create_gateway_app(transport: httpx.AsyncBaseTransport | None = None) -> FastAPI:
+    """Create a no-secret gateway; an injected transport enables hermetic tests."""
+
+    upstream_client = httpx.AsyncClient(
+        timeout=httpx.Timeout(10.0, connect=2.0),
+        limits=httpx.Limits(max_connections=100, max_keepalive_connections=20),
+        follow_redirects=False,
+        transport=transport,
+        trust_env=False,
+    )
+    # Drop httpx convenience defaults; Host and body framing are added by the protocol layer.
+    upstream_client.headers.clear()
+
+    @asynccontextmanager
+    async def lifespan(_: FastAPI) -> AsyncIterator[None]:
+        try:
+            yield
+        finally:
+            await upstream_client.aclose()
+
+    gateway = FastAPI(
+        title="Geological RAG Gateway",
+        docs_url=None,
+        redoc_url=None,
+        openapi_url=None,
+        lifespan=lifespan,
+    )
+
+    @gateway.get("/gateway/live", include_in_schema=False)
+    async def gateway_live() -> dict[str, str]:
+        return {"status": "ok"}
+
+    @gateway.api_route("/{path:path}", methods=SUPPORTED_METHODS, include_in_schema=False)
+    async def proxy(request: Request, path: str) -> Response:  # noqa: ARG001
+        body = await _bounded_body(request)
+        if body is None:
+            return JSONResponse(
+                status_code=status.HTTP_413_CONTENT_TOO_LARGE,
+                content={"detail": "request body too large"},
+            )
+
+        upstream_request = upstream_client.build_request(
+            request.method,
+            _upstream_url(request),
+            headers=_allowlisted_headers(request.headers, REQUEST_HEADER_ALLOWLIST),
+            content=body,
+        )
+        try:
+            upstream_response = await upstream_client.send(upstream_request)
+        except httpx.RequestError:
+            return JSONResponse(
+                status_code=status.HTTP_502_BAD_GATEWAY,
+                content={"detail": "upstream unavailable"},
+            )
+
+        return Response(
+            content=upstream_response.content,
+            status_code=upstream_response.status_code,
+            headers=_allowlisted_headers(
+                upstream_response.headers,
+                RESPONSE_HEADER_ALLOWLIST,
+            ),
+        )
+
+    return gateway
+
+
+app = create_gateway_app()
diff --git a/backend/app/main.py b/backend/app/main.py
index 79b0d4f..b5c988f 100644
--- a/backend/app/main.py
+++ b/backend/app/main.py
@@ -1,39 +1,51 @@
-"""Minimal FastAPI entrypoint; product endpoints are added in stage 2."""
+"""FastAPI entrypoint with dependency-free liveness and database readiness probes."""
 
 from typing import Any
 
 import psycopg
 import uvicorn
-from fastapi import FastAPI, HTTPException, status
+from fastapi import FastAPI, Response, status
 
 from app import __version__
+from app.api.v1 import demo_router
 from app.core.config import get_settings
 from app.core.secrets import SecretFileError
 
 app = FastAPI(title="Geological RAG API", version=__version__)
+app.include_router(demo_router)
+
+type HealthPayload = dict[str, str | dict[str, str]]
 
 
+@app.get("/health/live", tags=["health"])
 @app.get("/api/v1/health/live", tags=["health"])
 def live() -> dict[str, str]:
     return {"status": "ok", "version": __version__}
 
 
+@app.get(
+    "/health/ready",
+    tags=["health"],
+    responses={status.HTTP_503_SERVICE_UNAVAILABLE: {"description": "Database unavailable"}},
+)
 @app.get("/api/v1/health/ready", tags=["health"])
-def ready() -> dict[str, str]:
+def ready(response: Response) -> HealthPayload:
     settings = get_settings()
     try:
         dsn = settings.database_url().set(drivername="postgresql")
         with psycopg.connect(
             dsn.render_as_string(hide_password=False),
             connect_timeout=2,
+            autocommit=True,
         ) as connection:
-            connection.execute("SELECT 1")
-    except (OSError, SecretFileError, psycopg.Error) as exc:
-        raise HTTPException(
-            status_code=status.HTTP_503_SERVICE_UNAVAILABLE,
-            detail="database unavailable",
-        ) from exc
-    return {"status": "ready"}
+            result = connection.execute("SELECT 1").fetchone()
+            if result != (1,):
+                raise psycopg.DatabaseError("readiness query returned an unexpected result")
+    except (OSError, SecretFileError, psycopg.Error):
+        # Do not expose connection strings, secret paths, hostnames, or driver errors.
+        response.status_code = status.HTTP_503_SERVICE_UNAVAILABLE
+        return {"status": "not_ready", "checks": {"database": "unavailable"}}
+    return {"status": "ready", "checks": {"database": "ok"}}
 
 
 @app.get("/api/v1/meta", tags=["meta"])
@@ -52,5 +64,5 @@ def meta() -> dict[str, Any]:
 
 
 if __name__ == "__main__":
-    # Container ingress is controlled by Compose; only the edge proxy publishes a port.
+    # Compose publishes this listener only on the host loopback interface.
     uvicorn.run("app.main:app", host="0.0.0.0", port=8000)  # noqa: S104
diff --git a/backend/app/tools/seed_demo.py b/backend/app/tools/seed_demo.py
index 8b5a132..89a769b 100644
--- a/backend/app/tools/seed_demo.py
+++ b/backend/app/tools/seed_demo.py
@@ -23,14 +23,17 @@ from psycopg.types.json import Jsonb
 from app.adapters.bailian import BailianEmbeddingAdapter, BailianRerankerAdapter
 from app.adapters.fake import FakeEmbeddingProvider, FakeReranker, lexical_features
 from app.core.config import Settings
+from app.core.demo_identity import (
+    ACCESS_SCOPE_ID,
+    IDENTITY_NAMESPACE,
+    KNOWLEDGE_BASE_ID,
+    offline_embedding_profile_hash,
+)
 from app.core.secrets import SecretFileError
 from app.ports.model_providers import EmbeddingProvider, ModelProviderError, Reranker
 
 PROJECT_ROOT = Path(__file__).resolve().parents[3]
 DEFAULT_SAMPLE_ROOT = PROJECT_ROOT / "data" / "samples" / "public"
-IDENTITY_NAMESPACE = uuid.UUID("eef85571-1f64-4a09-86d7-53fd329c3eb2")
-KNOWLEDGE_BASE_ID = uuid.uuid5(IDENTITY_NAMESPACE, "synthetic-demo-knowledge-base")
-ACCESS_SCOPE_ID = uuid.uuid5(IDENTITY_NAMESPACE, "synthetic-demo-public-scope")
 
 
 @dataclass(frozen=True, slots=True)
@@ -139,13 +142,12 @@ def load_queries(path: Path) -> list[DemoQuery]:
 
 
 def embedding_profile_hash(settings: Settings, mode: str) -> str:
-    endpoint_identity = "local-fake"
-    model = "fake-feature-hash-v1"
-    api_mode = "deterministic-offline"
-    if mode == "bailian":
-        endpoint_identity = sha256_text(urlsplit(settings.bailian_openai_base_url).hostname or "")
-        model = settings.embedding_model
-        api_mode = "openai-compatible"
+    if mode != "bailian":
+        return offline_embedding_profile_hash(settings.embedding_dimension)
+
+    endpoint_identity = sha256_text(urlsplit(settings.bailian_openai_base_url).hostname or "")
+    model = settings.embedding_model
+    api_mode = "openai-compatible"
     profile = {
         "api_mode": api_mode,
         "dimension": settings.embedding_dimension,
diff --git a/backend/tests/integration/test_schema_contract.py b/backend/tests/integration/test_schema_contract.py
index 2712632..2653c32 100644
--- a/backend/tests/integration/test_schema_contract.py
+++ b/backend/tests/integration/test_schema_contract.py
@@ -17,6 +17,8 @@ from app.persistence.job_queue_sql import (  # noqa: E402
 )
 
 COMPOSE = (ROOT / "compose.yaml").read_text(encoding="utf-8")
+DOCKERFILE = (BACKEND / "Dockerfile").read_text(encoding="utf-8")
+DEMO_API = (BACKEND / "app/api/v1/demo.py").read_text(encoding="utf-8")
 BOOTSTRAP = (ROOT / "ops/postgres/init/10-bootstrap-rag.sh").read_text(encoding="utf-8")
 MIGRATION = (BACKEND / "migrations/versions/0001_initial_schema.py").read_text(encoding="utf-8")
 
@@ -31,6 +33,8 @@ def _service_block(name: str) -> str:
 def test_compose_isolates_database_credentials_and_networks() -> None:
     db = _service_block("db")
     migrate = _service_block("migrate")
+    api = _service_block("api")
+    gateway = _service_block("gateway")
     provider_smoke = _service_block("provider-smoke")
     seed_demo = _service_block("seed-demo")
     seed_demo_offline = _service_block("seed-demo-offline")
@@ -43,6 +47,27 @@ def test_compose_isolates_database_credentials_and_networks() -> None:
     assert "postgres_bootstrap_password" not in migrate
     assert "postgres_app_password" not in migrate
 
+    assert "postgres_app_password" in api
+    assert "postgres_bootstrap_password" not in api
+    assert "postgres_migrator_password" not in api
+    assert "bailian_api_key" not in api
+    assert '"127.0.0.1:8000:8000"' not in api
+    assert "      - data" in api
+    assert "      - edge" not in api
+    assert "      - egress" not in api
+    assert "read_only: true" in api
+    assert "no-new-privileges:true" in api
+    assert "cap_drop:" in api and "      - ALL" in api
+
+    assert '"127.0.0.1:8000:8000"' in gateway
+    assert "      - edge" in gateway
+    assert "      - data" in gateway
+    assert "secrets:" not in gateway
+    assert "POSTGRES_" not in gateway
+    assert "BAILIAN_" not in gateway
+    assert "read_only: true" in gateway
+    assert "no-new-privileges:true" in gateway
+
     assert "bailian_api_key" in provider_smoke
     assert "postgres_" not in provider_smoke
 
@@ -61,6 +86,34 @@ def test_compose_isolates_database_credentials_and_networks() -> None:
     assert re.search(r"(?m)^  edge:$", COMPOSE)
     assert re.search(r"(?m)^  egress:$", COMPOSE)
 
+    assert "USER 10001:10001" in DOCKERFILE
+    assert 'CMD ["uvicorn", "app.main:app"' in DOCKERFILE
+
+
+def test_demo_queries_pin_governed_offline_identity() -> None:
+    normalized = " ".join(DEMO_API.split())
+
+    for required_filter in (
+        "chunk.knowledge_base_id = %s",
+        "chunk.access_scope_id = %s",
+        "chunk.metadata ->> 'source_type' = 'synthetic'",
+        "chunk.searchable IS TRUE",
+        "chunk.index_status = 'READY'",
+        "chunk.approval_status = 'CLOUD_APPROVED'",
+        "document.active_version_id = chunk.document_version_id",
+        "version.review_state = 'CLOUD_APPROVED'",
+        "version.outbound_manifest_sha256 = chunk.outbound_manifest_sha256",
+        "version.embedding_profile_hash = chunk.embedding_profile_hash",
+        "chunk.embedding_model = %s",
+        "chunk.embedding_profile_hash = %s",
+    ):
+        assert required_filter in normalized
+
+    assert "KNOWLEDGE_BASE_ID" in DEMO_API
+    assert "ACCESS_SCOPE_ID" in DEMO_API
+    assert "DEMO_FAKE_EMBEDDING_MODEL" in DEMO_API
+    assert "offline_embedding_profile_hash" in DEMO_API
+
 
 def test_database_health_requires_tcp_and_atomic_bootstrap_sentinel() -> None:
     db = _service_block("db")
diff --git a/backend/tests/unit/test_demo_api.py b/backend/tests/unit/test_demo_api.py
new file mode 100644
index 0000000..c9dde9c
--- /dev/null
+++ b/backend/tests/unit/test_demo_api.py
@@ -0,0 +1,224 @@
+from __future__ import annotations
+
+from dataclasses import dataclass
+
+import httpx
+import psycopg
+import pytest
+from fastapi import FastAPI
+
+from app.api.v1.demo import (
+    DemoCandidate,
+    DemoCounts,
+    DemoRepository,
+    get_demo_repository,
+    make_citation_id,
+    make_page_label,
+    router,
+)
+
+
+@dataclass
+class StubRepository:
+    count_result: DemoCounts
+    candidates: list[DemoCandidate]
+    failure: psycopg.Error | None = None
+
+    def counts(self) -> DemoCounts:
+        if self.failure is not None:
+            raise self.failure
+        return self.count_result
+
+    def search(self, query_vector: tuple[float, ...], *, limit: int) -> list[DemoCandidate]:
+        if self.failure is not None:
+            raise self.failure
+        assert len(query_vector) == 1024
+        return self.candidates[:limit]
+
+
+def create_app(repository: DemoRepository) -> FastAPI:
+    app = FastAPI()
+    app.include_router(router)
+    app.dependency_overrides[get_demo_repository] = lambda: repository
+    return app
+
+
+@pytest.mark.asyncio
+async def test_status_reports_only_public_synthetic_counts() -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=20, vectors=20, searchable=20),
+            candidates=[],
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.get("/api/v1/demo/status")
+
+    assert response.status_code == 200
+    assert response.json() == {
+        "status": "ready",
+        "dataset": "synthetic-demo",
+        "counts": {"chunks": 20, "vectors": 20, "searchable": 20},
+    }
+
+
+@pytest.mark.asyncio
+async def test_status_explicitly_reports_empty_dataset() -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=0, vectors=0, searchable=0),
+            candidates=[],
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.get("/api/v1/demo/status")
+
+    assert response.status_code == 200
+    assert response.json()["status"] == "empty_dataset"
+
+
+@pytest.mark.asyncio
+async def test_status_does_not_mark_a_partial_demo_index_ready() -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=20, vectors=19, searchable=18),
+            candidates=[],
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.get("/api/v1/demo/status")
+
+    assert response.status_code == 200
+    assert response.json()["status"] == "incomplete_dataset"
+
+
+@pytest.mark.asyncio
+async def test_search_embeds_reranks_and_returns_only_safe_fields() -> None:
+    repository = StubRepository(
+        count_result=DemoCounts(chunks=2, vectors=2, searchable=2),
+        candidates=[
+            DemoCandidate(
+                source_key="internal-chunk-one",
+                title="西岭铜矿化合成记录",
+                text="该合成记录描述花岗斑岩接触带，未包含真实矿权或人员信息。",
+                page_start=3,
+                page_end=3,
+            ),
+            DemoCandidate(
+                source_key="internal-chunk-two",
+                title="北谷金异常合成记录",
+                text="北谷合成样点出现低强度金异常，仅用于离线验证。",
+                page_start=7,
+                page_end=8,
+            ),
+        ],
+    )
+    app = create_app(repository)
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.post(
+            "/api/v1/demo/search",
+            json={"query": "花岗斑岩 铜矿化", "top_k": 1},
+        )
+
+    assert response.status_code == 200
+    payload = response.json()
+    assert payload["status"] == "ok"
+    assert payload["dataset"] == "synthetic-demo"
+    assert len(payload["results"]) == 1
+    result = payload["results"][0]
+    assert set(result) == {"title", "snippet", "page_label", "score", "citation_id"}
+    assert result["title"].startswith("合成资料｜")
+    assert result["page_label"] == "第 3 页"
+    assert result["citation_id"] == make_citation_id("internal-chunk-one")
+    assert "internal-chunk-one" not in str(payload)
+    assert "manifest" not in str(payload).lower()
+    assert "sha256" not in str(payload).lower()
+
+
+@pytest.mark.asyncio
+async def test_search_returns_explicit_empty_dataset_state() -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=0, vectors=0, searchable=0),
+            candidates=[],
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.post(
+            "/api/v1/demo/search",
+            json={"query": "不存在的合成资料", "top_k": 3},
+        )
+
+    assert response.status_code == 200
+    assert response.json() == {
+        "status": "empty_dataset",
+        "dataset": "synthetic-demo",
+        "results": [],
+    }
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize(
+    "body",
+    [
+        {"query": "   ", "top_k": 3},
+        {"query": "x" * 501, "top_k": 3},
+        {"query": "铜矿", "top_k": 0},
+        {"query": "铜矿", "top_k": 11},
+    ],
+)
+async def test_search_rejects_invalid_bounded_input(body: dict[str, object]) -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=0, vectors=0, searchable=0),
+            candidates=[],
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        response = await client.post("/api/v1/demo/search", json=body)
+
+    assert response.status_code == 422
+
+
+@pytest.mark.asyncio
+@pytest.mark.parametrize("path", ["/api/v1/demo/status", "/api/v1/demo/search"])
+async def test_database_failure_is_sanitized_as_503(path: str) -> None:
+    app = create_app(
+        StubRepository(
+            count_result=DemoCounts(chunks=0, vectors=0, searchable=0),
+            candidates=[],
+            failure=psycopg.OperationalError("host=db password=must-not-leak"),
+        )
+    )
+    async with httpx.AsyncClient(
+        transport=httpx.ASGITransport(app=app), base_url="http://test"
+    ) as client:
+        if path.endswith("search"):
+            response = await client.post(path, json={"query": "铜矿", "top_k": 3})
+        else:
+            response = await client.get(path)
+
+    assert response.status_code == 503
+    assert response.json() == {"detail": "database unavailable"}
+    assert "must-not-leak" not in response.text
+
+
+def test_citation_and_page_labels_are_stable_and_opaque() -> None:
+    first = make_citation_id("private-database-uuid")
+    assert first == make_citation_id("private-database-uuid")
+    assert first != make_citation_id("another-private-database-uuid")
+    assert "private" not in first
+    assert make_page_label(None, None) == "页码未知"
+    assert make_page_label(2, 4) == "第 2-4 页"
diff --git a/backend/tests/unit/test_gateway.py b/backend/tests/unit/test_gateway.py
new file mode 100644
index 0000000..3628098
--- /dev/null
+++ b/backend/tests/unit/test_gateway.py
@@ -0,0 +1,163 @@
+import json
+from collections.abc import AsyncIterator, Callable
+from contextlib import asynccontextmanager
+
+import httpx
+import pytest
+from fastapi import FastAPI
+
+from app.gateway import MAX_REQUEST_BODY_BYTES, create_gateway_app
+
+type Handler = Callable[[httpx.Request], httpx.Response]
+
+
+@asynccontextmanager
+async def _gateway_client(handler: Handler) -> AsyncIterator[httpx.AsyncClient]:
+    gateway = create_gateway_app(httpx.MockTransport(handler))
+    async with gateway.router.lifespan_context(gateway):
+        transport = httpx.ASGITransport(app=gateway)
+        async with httpx.AsyncClient(transport=transport, base_url="http://gateway") as client:
+            yield client
+
+
+@pytest.mark.asyncio
+async def test_gateway_live_and_docs_are_disabled() -> None:
+    gateway = create_gateway_app(httpx.MockTransport(lambda _: httpx.Response(500)))
+    try:
+        assert gateway.docs_url is None
+        assert gateway.redoc_url is None
+        assert gateway.openapi_url is None
+
+        transport = httpx.ASGITransport(app=gateway)
+        async with httpx.AsyncClient(transport=transport, base_url="http://gateway") as client:
+            response = await client.get("/gateway/live")
+        assert response.status_code == 200
+        assert response.json() == {"status": "ok"}
+    finally:
+        await _close_gateway(gateway)
+
+
+async def _close_gateway(gateway: FastAPI) -> None:
+    async with gateway.router.lifespan_context(gateway):
+        pass
+
+
+@pytest.mark.asyncio
+async def test_successful_get_preserves_path_query_and_allowed_header() -> None:
+    seen: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append(request)
+        return httpx.Response(200, json={"result": "ok"}, headers={"x-request-id": "req-1"})
+
+    async with _gateway_client(handler) as client:
+        response = await client.get(
+            "/api/v1/search?q=granite%20deposit&limit=5",
+            headers={"x-request-id": "req-1", "x-forwarded-host": "evil.invalid"},
+        )
+
+    assert response.status_code == 200
+    assert response.json() == {"result": "ok"}
+    assert response.headers["x-request-id"] == "req-1"
+    assert seen[0].url == "http://api:8000/api/v1/search?q=granite%20deposit&limit=5"
+    assert seen[0].headers["host"] == "api:8000"
+    assert "x-forwarded-host" not in seen[0].headers
+
+
+@pytest.mark.asyncio
+async def test_post_json_body_and_content_type_are_forwarded() -> None:
+    seen: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append(request)
+        return httpx.Response(201, json={"accepted": True})
+
+    async with _gateway_client(handler) as client:
+        response = await client.post("/api/v1/query", json={"question": "Where is gold?"})
+
+    assert response.status_code == 201
+    assert response.json() == {"accepted": True}
+    assert seen[0].method == "POST"
+    assert seen[0].headers["content-type"] == "application/json"
+    assert json.loads(seen[0].content) == {"question": "Where is gold?"}
+
+
+@pytest.mark.asyncio
+async def test_upstream_origin_is_fixed_against_host_and_path_ssrf_attempts() -> None:
+    seen: list[httpx.Request] = []
+
+    def handler(request: httpx.Request) -> httpx.Response:
+        seen.append(request)
+        return httpx.Response(200)
+
+    async with _gateway_client(handler) as client:
+        response = await client.get(
+            "//evil.invalid/http://metadata.internal/latest?target=http://attacker.invalid",
+            headers={"host": "attacker.invalid", "forwarded": "host=attacker.invalid"},
+        )
+
+    assert response.status_code == 200
+    assert seen[0].url.scheme == "http"
+    assert seen[0].url.host == "api"
+    assert seen[0].url.port == 8000
+    assert seen[0].headers["host"] == "api:8000"
+    assert "forwarded" not in seen[0].headers
+
+
+@pytest.mark.asyncio
+async def test_request_larger_than_one_mib_is_rejected_before_upstream() -> None:
+    upstream_calls = 0
+
+    def handler(_: httpx.Request) -> httpx.Response:
+        nonlocal upstream_calls
+        upstream_calls += 1
+        return httpx.Response(200)
+
+    async with _gateway_client(handler) as client:
+        response = await client.post("/upload", content=b"x" * (MAX_REQUEST_BODY_BYTES + 1))
+
+    assert response.status_code == 413
+    assert response.json() == {"detail": "request body too large"}
+    assert upstream_calls == 0
+
+
+@pytest.mark.asyncio
+async def test_upstream_transport_error_returns_redacted_502() -> None:
+    def handler(request: httpx.Request) -> httpx.Response:
+        raise httpx.ConnectError(
+            "api:8000 refused connection with internal-token-value",
+            request=request,
+        )
+
+    async with _gateway_client(handler) as client:
+        response = await client.get("/api/v1/health/ready")
+
+    assert response.status_code == 502
+    assert response.json() == {"detail": "upstream unavailable"}
+    assert "api:8000" not in response.text
+    assert "internal-token-value" not in response.text
+
+
+@pytest.mark.asyncio
+async def test_sensitive_upstream_response_headers_are_not_forwarded() -> None:
+    def handler(_: httpx.Request) -> httpx.Response:
+        return httpx.Response(
+            200,
+            content=b"ok",
+            headers={
+                "content-type": "text/plain",
+                "cache-control": "no-store",
+                "set-cookie": "session=private",
+                "server": "internal-api",
+                "x-internal-token": "private",
+            },
+        )
+
+    async with _gateway_client(handler) as client:
+        response = await client.get("/status")
+
+    assert response.headers["content-type"] == "text/plain"
+    assert response.headers["cache-control"] == "no-store"
+    assert "set-cookie" not in response.headers
+    assert "server" not in response.headers
+    assert "x-internal-token" not in response.headers
diff --git a/backend/tests/unit/test_health_api.py b/backend/tests/unit/test_health_api.py
index 8a9c63a..9cb35ef 100644
--- a/backend/tests/unit/test_health_api.py
+++ b/backend/tests/unit/test_health_api.py
@@ -1,22 +1,82 @@
-import httpx
-import pytest
+from unittest.mock import MagicMock, patch
 
-from app.main import app
+import httpx
+import psycopg
+import pytest
+from sqlalchemy import URL
+
+from app import main
+
+
+class _SettingsStub:
+    def database_url(self) -> URL:
+        return URL.create(
+            "postgresql+psycopg",
+            username="app",
+            password="database-test-password",
+            host="db.internal",
+            port=5432,
+            database="rag",
+        )
 
 
 @pytest.mark.asyncio
 async def test_liveness_does_not_require_database_or_model_credentials() -> None:
-    transport = httpx.ASGITransport(app=app)
+    transport = httpx.ASGITransport(app=main.app)
     async with httpx.AsyncClient(transport=transport, base_url="http://test") as client:
-        response = await client.get("/api/v1/health/live")
+        response = await client.get("/health/live")
 
     assert response.status_code == 200
     assert response.json()["status"] == "ok"
 
 
+@pytest.mark.asyncio
+async def test_readiness_executes_select_one_and_returns_redacted_status() -> None:
+    connection = MagicMock()
+    connection.__enter__.return_value = connection
+    connection.execute.return_value.fetchone.return_value = (1,)
+
+    with (
+        patch.object(main, "get_settings", return_value=_SettingsStub()),
+        patch.object(psycopg, "connect", return_value=connection) as connect,
+    ):
+        transport = httpx.ASGITransport(app=main.app)
+        async with httpx.AsyncClient(transport=transport, base_url="http://test") as client:
+            response = await client.get("/health/ready")
+
+    assert response.status_code == 200
+    assert response.json() == {"status": "ready", "checks": {"database": "ok"}}
+    connection.execute.assert_called_once_with("SELECT 1")
+    assert connect.call_args.kwargs == {"connect_timeout": 2, "autocommit": True}
+    assert "database-test-password" not in response.text
+    assert "db.internal" not in response.text
+
+
+@pytest.mark.asyncio
+async def test_readiness_returns_503_without_exposing_database_error() -> None:
+    private_error = psycopg.OperationalError(
+        "could not connect to db.internal with database-test-password"
+    )
+    with (
+        patch.object(main, "get_settings", return_value=_SettingsStub()),
+        patch.object(psycopg, "connect", side_effect=private_error),
+    ):
+        transport = httpx.ASGITransport(app=main.app)
+        async with httpx.AsyncClient(transport=transport, base_url="http://test") as client:
+            response = await client.get("/health/ready")
+
+    assert response.status_code == 503
+    assert response.json() == {
+        "status": "not_ready",
+        "checks": {"database": "unavailable"},
+    }
+    assert "database-test-password" not in response.text
+    assert "db.internal" not in response.text
+
+
 @pytest.mark.asyncio
 async def test_meta_exposes_model_names_but_no_credentials() -> None:
-    transport = httpx.ASGITransport(app=app)
+    transport = httpx.ASGITransport(app=main.app)
     async with httpx.AsyncClient(transport=transport, base_url="http://test") as client:
         response = await client.get("/api/v1/meta")
 
diff --git a/compose.yaml b/compose.yaml
index 2c29d07..3db8b5e 100644
--- a/compose.yaml
+++ b/compose.yaml
@@ -81,6 +81,76 @@ services:
       - data
     restart: "no"
 
+  api:
+    build:
+      context: ./backend
+    command: ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]
+    depends_on:
+      db:
+        condition: service_healthy
+      migrate:
+        condition: service_completed_successfully
+    environment: *runtime-config
+    secrets:
+      - postgres_app_password
+    networks:
+      - data
+    healthcheck:
+      test:
+        - CMD
+        - python
+        - -c
+        - >-
+          import urllib.request;
+          urllib.request.urlopen('http://127.0.0.1:8000/health/ready', timeout=2)
+      interval: 10s
+      timeout: 3s
+      retries: 5
+      start_period: 5s
+    init: true
+    read_only: true
+    tmpfs:
+      - /tmp
+    security_opt:
+      - no-new-privileges:true
+    cap_drop:
+      - ALL
+    restart: unless-stopped
+
+  gateway:
+    build:
+      context: ./backend
+    command: ["uvicorn", "app.gateway:app", "--host", "0.0.0.0", "--port", "8000"]
+    depends_on:
+      api:
+        condition: service_healthy
+    ports:
+      - "127.0.0.1:8000:8000"
+    networks:
+      - edge
+      - data
+    healthcheck:
+      test:
+        - CMD
+        - python
+        - -c
+        - >-
+          import urllib.request;
+          urllib.request.urlopen('http://127.0.0.1:8000/health/ready', timeout=2)
+      interval: 10s
+      timeout: 3s
+      retries: 5
+      start_period: 5s
+    init: true
+    read_only: true
+    tmpfs:
+      - /tmp
+    security_opt:
+      - no-new-privileges:true
+    cap_drop:
+      - ALL
+    restart: unless-stopped
+
   provider-smoke:
     build:
       context: ./backend
diff --git a/docs/04-project-todo.md b/docs/04-project-todo.md
index 97d4516..85952b9 100644
--- a/docs/04-project-todo.md
+++ b/docs/04-project-todo.md
@@ -7,7 +7,7 @@
 | 已完成阶段 | Stage 0：仓库、安全和设计基线 |
 | 整体完成度 | 约 12%，合理区间 10%–15% |
 | 设计完成度 | 设计基线已完成；实现中发现新约束时继续通过 ADR 和文档修订维护 |
-| 业务代码完成度 | 约 8%；Stage 1 的离线/数据库 PoC 已验收，真实百炼 smoke 仍待新 Key，前端产品功能尚未实现 |
+| 业务代码完成度 | 约 10%；Stage 1 的 Docker API、离线检索和数据库 PoC 已验收，真实百炼 smoke 仍待新 Key，前端产品功能尚未实现 |
 | 当前预计剩余工期 | 约 9–13 周，含 300 题正式标注、盲测、论文和答辩缓冲 |
 | 进度权威来源 | 本文的阶段状态、验收证据和已推送提交 |
 
@@ -50,7 +50,7 @@
 | Stage 9 答辩、发布与归档 | 3% | `TODO` | 0% |
 | **合计** | **100%** | — | **12%** |
 
-Stage 1 已完成可离线验收的数据库、适配器契约和 synthetic seed 子闭环，阶段内部约完成 85%；但真实三模型 smoke 仍依赖轮换后的新 Key，因此 Stage 1 不提前计入整体里程碑。本文复选框表示“已通过验收”，不表示“文件是否已经出现”。当前可诚实表述为：**设计基线完成，整体里程碑约 12%，Stage 1 离线部分可运行，真实百炼验证尚未完成。**
+Stage 1 已完成可离线验收的数据库、适配器契约、synthetic seed 和只读 API 子闭环，阶段内部约完成 90%；但真实三模型 smoke 仍依赖轮换后的新 Key，因此 Stage 1 不提前计入整体里程碑。本文复选框表示“已通过验收”，不表示“文件是否已经出现”。当前可诚实表述为：**设计基线完成，整体里程碑约 12%，Stage 1 离线后端可运行，真实百炼验证尚未完成。**
 
 ## 2. 阶段依赖与关键路径
 
@@ -134,6 +134,7 @@ Stage 0 DONE
 - [x] 创建 `backend/pyproject.toml` 和依赖锁文件，不引入未说明依赖。
 - [x] 创建最小 `backend/Dockerfile`，使用非 root 用户和固定基础镜像 digest。
 - [x] 创建最小 `compose.yaml`，包含 `db + migrate + provider-smoke + seed-demo/offline`。
+- [x] 启动最小 FastAPI `api + gateway`，内部 API 无 egress，gateway 无 Secret 并仅发布回环端口；提供真实数据库 readiness、Swagger 和只读 synthetic demo 检索。
 - [x] 创建 PostgreSQL bootstrap、migrator 和 app 分权角色初始化脚本；备份只读角色在备份功能落地时单独创建。
 - [x] 创建 Alembic 基线迁移，启用 pgvector 并建立 1024 维向量表/HNSW 基线。
 - [x] 确保运行期服务不挂载 bootstrap 或 migrator Secret。
@@ -162,8 +163,9 @@ Stage 0 DONE
 - [x] `docker compose up db migrate` 在空 volume 成功建立扩展、角色和表。
 - [ ] `docker compose run --rm provider-smoke` 三模型探测成功，日志无 Secret。
 - [x] `docker compose run --rm seed-demo-offline` 完成 20 条虚构数据写入、检索和重排；真实模式待新 Key。
+- [x] `api + gateway` 镜像构建并达到 healthy；live/ready/meta/demo status/demo search 均通过真实 HTTP 验收。
 - [x] 第二次运行 seed 后数据库计数与第一次相同，均为 chunks/vectors/searchable = 20/20/20。
-- [x] 41 项测试证明 Embedding 维度/下标、Rerank 下标、Chat 流式响应和失败路径正确。
+- [x] 63 项测试证明模型契约、健康检查、固定上游 gateway、离线 demo、数据治理和失败路径正确。
 - [x] `make verify`、Secret 扫描、固定镜像构建和 `git diff --check` 通过。
 
 ### 2026-07-12 已验证运行证据
@@ -171,6 +173,8 @@ Stage 0 DONE
 - 全新 volume 上 `db` 达到 healthy，`migrate` 以非超级用户退出码 0，版本为 `0001_initial_schema`。
 - `vector` 扩展与 HNSW 基线存在；app/migrator 均非超级用户，app 无 `rag` schema DDL 权限但具有所需 DML。
 - 两次离线 seed 均输出 20/20/20，9 个可回答虚构问题 Hit@3 = 9/9。
+- FastAPI 容器使用 app 最小权限角色，根文件系统只读且无 egress；无 Secret gateway 仅提供回环入口；Swagger 可见，demo search 返回合成片段与不透明 citation ID。
+- API 容器对公网 TCP 探测返回 `ENETUNREACH (101)`；gateway 的 mounts 为空且不含数据库或百炼业务环境变量。
 - PostgreSQL 重启后计数仍为 20/20/20。
 - app 尝试修改已 `CLOUD_APPROVED` 的 `cloud_text` 被审批不可变触发器拒绝；尝试建表被权限拒绝。
 - 唯一未验收项是真实 `text-embedding-v4` / `qwen3-rerank` / `deepseek-v4-flash` smoke 与真实模式 seed。
@@ -180,6 +184,7 @@ Stage 0 DONE
 - [x] `S1-A`：数据库初始化、分权角色、迁移和最小 Compose 已随 `f4ba5d5` 验证并推送。
 - [ ] `S1-B`：三模型适配器和 fake 契约测试已随 `f4ba5d5` 推送；新 Key 下的 live smoke 未完成，因此节点保持未完成。
 - [x] `S1-C`：20 条虚构 seed、幂等验证、运行证据和文档已随 `f4ba5d5` 推送。
+- [ ] `S1-D`：内部 API、无 Secret gateway、只读 demo 检索和真实 HTTP/Docker 运行证据；验证后提交并推送。
 
 `f4ba5d5` 是 Stage 1 离线可执行闭环提交，不代表 Stage 1 已完成；阶段完成仍以真实三模型 smoke 和真实模式 seed 通过为准。
 
diff --git a/docs/05-stage1-runbook.md b/docs/05-stage1-runbook.md
index d399aae..612fbf0 100644
--- a/docs/05-stage1-runbook.md
+++ b/docs/05-stage1-runbook.md
@@ -21,7 +21,7 @@ bash scripts/init-local-secrets.sh
 离线模式使用确定性的 1024 维 feature-hash 向量和词法重排器，只验证数据治理、批处理、迁移、向量写入、权限过滤、检索、重排和幂等性，不把它当成真实模型质量。
 
 ```bash
-docker compose up -d --build db migrate
+docker compose up -d --build gateway
 docker compose --profile tools run --rm seed-demo-offline
 docker compose --profile tools run --rm seed-demo-offline
 ```
@@ -44,6 +44,28 @@ Seed 的实际流程是：
 7. 对 Top K 候选重排并输出虚构问题的 Hit@3；
 8. 相同输入再次执行使用相同 ID 和幂等 upsert，不增加行数。
 
+### 2.1 查看后端运行效果
+
+内部 API 只连接 `internal` data 网络，只挂载 app 数据库 Secret，不连接外网，也不挂载百炼 Key。无 Secret、无数据库凭证的 gateway 同时连接 ingress 与 data 网络，并且仅发布到本机回环地址 `127.0.0.1:8000`。两个容器都以数值非 root 用户运行，根文件系统只读，并移除 Linux capabilities。
+
+```bash
+curl http://127.0.0.1:8000/health/live
+curl http://127.0.0.1:8000/health/ready
+curl http://127.0.0.1:8000/api/v1/demo/status
+curl -X POST http://127.0.0.1:8000/api/v1/demo/search \
+  -H 'Content-Type: application/json' \
+  --data '{"query":"花岗斑岩铜矿化特征","top_k":3}'
+```
+
+预期结果：
+
+- readiness 返回 `database=ok`；
+- demo status 返回 chunks/vectors/searchable = 20/20/20；
+- search 只返回 `synthetic-demo` 数据集中的合成标题、批准后的片段、页码、分数和不透明 citation ID；
+- Swagger 位于 <http://127.0.0.1:8000/docs>。
+
+该接口是 Stage 1 的离线可见效果，不调用百炼，也不代表完整问答生成链或 React 前端已经完成。
+
 ## 3. 真实百炼能力探测
 
 完成旧 Key 轮换后：