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

docs/01-data-and-evaluation.md

@@ -443,7 +443,7 @@ embedding_cache_key = SHA256(
 chunk_embedding_assignment = UNIQUE(chunk_id, embedding_profile_hash)
 ```
 
-相同文本可以安全复用向量缓存，但每个 chunk 都必须建立独立 assignment，不能用缓存键替代任务/行唯一键。模型别名无法解析到稳定 revision 时，每次冻结实验显式设置 `cache_epoch`，避免别名漂移后复用旧向量。激活前再次核对当前 `embedding_text_sha256`、完整 profile 与 assignment；任何一项变化都生成新索引版本。
+相同文本可以安全复用向量缓存，但每个 chunk 都必须建立独立 assignment，不能用缓存键替代任务/行唯一键。模型别名无法解析到稳定 revision 时，每次冻结实验显式设置 `cache_epoch`，并把它纳入不可变的 `embedding_profile_hash`；epoch 变化必须创建新 profile，禁止原地修改 profile 后继续复用旧缓存。激活前再次核对当前 `embedding_text_sha256`、完整 profile 与 assignment；任何一项变化都生成新索引版本。
 
 `endpoint_identity_hash` 由规范化后的工作空间/部署端点身份计算，仅保存哈希而不在实验导出中暴露真实工作空间。这样同地域、同模型别名但不同 MaaS 工作空间的向量不会错误共用缓存。