Isolate cloud model access before enabling product RAG workflows

The API and ingestion tools now use a fixed internal model gateway while
governed profiles, embedding cache assignments, traceable citations, and
stable API errors establish the boundaries required by later workflows.

Constraint: The current Alibaba Cloud workspace rejects all three live model calls with authentication failures
Rejected: Give the API or seed tools the Bailian key and direct egress | combines database access, cloud credentials, and public network access
Rejected: Mix offline and Bailian vectors in one demo namespace | makes profile activation and retrieval ambiguous
Confidence: high
Scope-risk: moderate
Reversibility: clean
Directive: Keep Bailian credentials and egress exclusive to model-gateway and create a new immutable profile hash for any embedding identity change
Tested: make verify; 121 backend tests; 14 frontend tests; fresh and populated Alembic upgrade-downgrade-upgrade; two idempotent offline seeds; Docker health and HTTP retrieval; isolated provider smoke
Not-tested: Successful live Bailian responses because the supplied workspace credential currently fails authentication

backend/app/core/config.py

@@ -35,6 +35,11 @@ class Settings(BaseSettings):
     upload_root: Path = Path("/data/uploads")
     max_upload_mb: int = Field(default=100, ge=1, le=2048)
 
+    model_gateway_base_url: str = "http://model-gateway:8000"
+    model_gateway_token_file: Path = Path("/run/secrets/model_gateway_api_token")
+    model_gateway_caller: Literal["api", "worker"] = "api"
+    model_gateway_timeout_seconds: float = Field(default=120, gt=0, le=600)
+
     bailian_openai_base_url: str = (
         "https://<workspace-id>.cn-beijing.maas.aliyuncs.com/compatible-mode/v1"
     )
@@ -71,6 +76,24 @@ class Settings(BaseSettings):
     def normalize_base_url(cls, value: str) -> str:
         return value.rstrip("/")
 
+    @field_validator("model_gateway_base_url")
+    @classmethod
+    def validate_model_gateway_base_url(cls, value: str) -> str:
+        normalized = value.rstrip("/")
+        parsed = urlsplit(normalized)
+        if (
+            parsed.scheme != "http"
+            or parsed.hostname != "model-gateway"
+            or parsed.port != 8000
+            or parsed.path not in ("", "/")
+            or parsed.username is not None
+            or parsed.password is not None
+            or parsed.query
+            or parsed.fragment
+        ):
+            raise ValueError("MODEL_GATEWAY_BASE_URL must be the fixed internal service URL")
+        return normalized
+
     @field_validator("embedding_dimension", mode="before")
     @classmethod
     def parse_embedding_dimension(cls, value: object) -> int: