feat: M1 — 立项→写章草稿(SSE)→自动保存；连一家 provider

- 薄自建 LLM 网关：OpenAI 兼容适配器(DeepSeek) + instructor 结构化输出 + usage_ledger 记账 + 档位路由
- 记忆服务 assemble：确定性选择(显式+主角+近况) + 渲染卡 + 缓存断点(中性文本)
- LangGraph 写章节点 + Postgres checkpointer + SSE 归一(token/done/error)
- API：立项 + 写章 draft(SSE) + PUT 自动保存 + 提供商凭据(Fernet 加密/测试连接)
- 前端：AppShell + 作品库 + 5 步立项向导 + 写作工作台(流式打字机+自动保存) + 设置页
- M1 E2E：真实 DB + mock 网关零 token 走通闭环

apps/api/ww_api/routers/settings_providers.py

@@ -0,0 +1,127 @@
+"""提供商凭据与档位路由端点（C3 / ARCH §4.7, §7.2；UX §6.10）。
+
+- GET  /settings/providers       列出已配置提供商（掩码）+ 档位路由。
+- PUT  /settings/providers       幂等 upsert 凭据/档位路由，回掩码视图。
+- POST /settings/providers/test  最小探测验 Key + 拉能力矩阵。
+
+不变量：响应/日志绝不含明文 Key（加密入库、仅掩码出站）。
+"""
+
+from __future__ import annotations
+
+from typing import Annotated
+
+from fastapi import APIRouter, Depends
+from ww_config import get_settings
+from ww_llm_gateway.adapters.base import Capabilities
+
+from ww_api.logging_config import get_logger
+from ww_api.schemas.providers import (
+    CapabilitiesView,
+    ProvidersResponse,
+    ProvidersUpsertRequest,
+    ProviderView,
+    TestConnectionRequest,
+    TestConnectionResponse,
+    TierRoutingView,
+)
+from ww_api.security.credentials import encrypt_api_key, mask_api_key
+from ww_api.services.credentials import (
+    STUB_OWNER_ID,
+    CredentialStore,
+    ProviderProbe,
+    StoredCredential,
+    StoredRouting,
+)
+from ww_api.services.provider_deps import (
+    get_credential_store,
+    get_provider_probe,
+)
+
+log = get_logger("ww.api.providers")
+
+router = APIRouter(prefix="/settings/providers", tags=["settings"])
+
+StoreDep = Annotated[CredentialStore, Depends(get_credential_store)]
+ProbeDep = Annotated[ProviderProbe, Depends(get_provider_probe)]
+
+
+def _mask_credential(cred: StoredCredential, plaintext: str | None) -> ProviderView:
+    # 存储层只有密文；掩码需明文末四位——若没有则全隐占位。
+    masked = mask_api_key(plaintext) if plaintext is not None else mask_api_key("")
+    return ProviderView(provider=cred.provider, masked_key=masked)
+
+
+def _routing_view(r: StoredRouting) -> TierRoutingView:
+    return TierRoutingView(tier=r.tier, provider=r.provider, model=r.model, fallback=r.fallback)
+
+
+async def _build_response(store: CredentialStore) -> ProvidersResponse:
+    creds = await store.list_credentials(STUB_OWNER_ID)
+    routing = await store.list_routing()
+    # 列表视图无明文，掩码占位（不解密历史密文以免无谓 IO/泄露面）。
+    providers = [ProviderView(provider=c.provider, masked_key=mask_api_key("")) for c in creds]
+    return ProvidersResponse(
+        providers=providers,
+        tier_routing=[_routing_view(r) for r in routing],
+    )
+
+
+@router.get("")
+async def list_providers(store: StoreDep) -> ProvidersResponse:
+    return await _build_response(store)
+
+
+@router.put("")
+async def upsert_providers(
+    body: ProvidersUpsertRequest,
+    store: StoreDep,
+) -> ProvidersResponse:
+    enc_key = get_settings().credential_enc_key
+    for cred in body.credentials:
+        api_key_enc = encrypt_api_key(cred.api_key, key=enc_key)
+        await store.upsert_credential(STUB_OWNER_ID, cred.provider, api_key_enc)
+        # 仅记 provider + 末四位掩码，绝不记明文
+        log.info(
+            "provider_credential_upserted",
+            provider=cred.provider,
+            masked_key=mask_api_key(cred.api_key),
+        )
+    for routing in body.tier_routing:
+        await store.upsert_routing(
+            StoredRouting(
+                tier=routing.tier,
+                provider=routing.provider,
+                model=routing.model,
+                fallback=routing.fallback,
+            )
+        )
+        log.info(
+            "tier_routing_upserted",
+            tier=routing.tier,
+            provider=routing.provider,
+            model=routing.model,
+        )
+    return await _build_response(store)
+
+
+def _capabilities_view(caps: Capabilities) -> CapabilitiesView:
+    return CapabilitiesView(
+        structured_output=caps.structured_output,
+        prefix_cache=caps.prefix_cache,
+        thinking=caps.thinking,
+    )
+
+
+@router.post("/test")
+async def test_connection(
+    body: TestConnectionRequest,
+    probe: ProbeDep,
+) -> TestConnectionResponse:
+    caps = await probe.probe(STUB_OWNER_ID, body.provider)
+    log.info("provider_probe_ok", provider=body.provider)
+    return TestConnectionResponse(
+        provider=body.provider,
+        ok=True,
+        capabilities=_capabilities_view(caps),
+    )