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

packages/llm_gateway/tests/test_gateway.py

@@ -0,0 +1,82 @@
+"""T1.1 网关核心单测：run / stream / 记账 / 路由 / 错误。"""
+
+from __future__ import annotations
+
+import uuid
+
+import pytest
+from fakes import FakeAdapter, FakeLedger, fake_route
+from ww_llm_gateway.gateway import Gateway
+from ww_llm_gateway.routing import resolve_route
+from ww_llm_gateway.types import LlmRequest, Scope
+from ww_shared import AppError, ErrorCode
+
+
+async def test_run_returns_text_usage_and_served_by(req: LlmRequest) -> None:
+    adapter = FakeAdapter(text="第一章正文")
+    ledger = FakeLedger()
+    gw = Gateway({"deepseek": adapter}, ledger, resolver=fake_route)
+
+    resp = await gw.run(req)
+
+    assert resp.text == "第一章正文"
+    assert resp.served_by.provider == "deepseek"
+    assert resp.served_by.fell_back is False
+    assert resp.usage.input_tokens == 100
+    assert resp.usage.output_tokens == 50
+    assert adapter.complete_calls == 1
+
+
+async def test_run_writes_exactly_one_ledger_record(req: LlmRequest) -> None:
+    ledger = FakeLedger()
+    gw = Gateway({"deepseek": FakeAdapter()}, ledger, resolver=fake_route)
+
+    await gw.run(req)
+
+    assert len(ledger.records) == 1
+    assert ledger.records[0].provider == "deepseek"
+    assert ledger.records[0].model == "deepseek-chat"
+
+
+async def test_run_computes_cost_from_pricing(req: LlmRequest) -> None:
+    ledger = FakeLedger()
+    gw = Gateway({"deepseek": FakeAdapter()}, ledger, resolver=fake_route)
+
+    resp = await gw.run(req)
+
+    # ceil(100/1e6*27 + 50/1e6*110) == 1 cent
+    assert resp.usage.cost_minor == 1
+    assert resp.usage.currency == "USD"
+
+
+async def test_stream_yields_deltas_and_records_once(req: LlmRequest) -> None:
+    ledger = FakeLedger()
+    gw = Gateway({"deepseek": FakeAdapter(deltas=["a", "b", "c"])}, ledger, resolver=fake_route)
+
+    collected = [d.text async for d in gw.stream(req)]
+
+    assert "".join(collected) == "abc"
+    assert len(ledger.records) == 1
+    assert ledger.records[0].output_tokens == 50
+
+
+async def test_unknown_provider_raises_llm_unavailable(req: LlmRequest) -> None:
+    gw = Gateway({}, FakeLedger(), resolver=fake_route)
+
+    with pytest.raises(AppError) as exc:
+        await gw.run(req)
+
+    assert exc.value.code == ErrorCode.LLM_UNAVAILABLE
+
+
+def test_resolve_route_parses_tier_defaults() -> None:
+    route = resolve_route("writer")
+    assert route.provider == "deepseek"
+    assert route.model == "deepseek-chat"
+
+
+def test_agent_passes_only_tier_never_model() -> None:
+    # 不变量 ②：LlmRequest 无 model 字段，只有 tier
+    req = LlmRequest(tier="analyst", input="x", scope=Scope(user_id=uuid.UUID(int=9)))
+    assert "model" not in LlmRequest.model_fields
+    assert req.tier == "analyst"