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/ww_llm_gateway/gateway.py

@@ -0,0 +1,99 @@
+"""网关核心：路由 → 调用适配器 → 记账 → 返回（ARCH §4.1–4.3/§4.8）。
+
+M1 单 provider，无回退/熔断（那是 M5/T5.4）。流式经 `stream()` 归一为 `Delta`。
+日志脱敏：只记长度，绝不记原文/api key（不变量、§9.3）。
+"""
+
+from __future__ import annotations
+
+from collections.abc import AsyncIterator, Callable
+
+import structlog
+from ww_shared import AppError, ErrorCode
+
+from .adapters.base import ProviderAdapter, ProviderUsage
+from .ledger import LedgerSink
+from .pricing import cost_minor
+from .routing import Route, resolve_route
+from .types import Delta, LlmRequest, LlmResponse, ServedBy, Tier, Usage
+
+log = structlog.get_logger(__name__)
+
+
+def _input_len(req: LlmRequest) -> int:
+    if isinstance(req.input, str):
+        return len(req.input)
+    return sum(len(b.text) for b in req.input)
+
+
+class Gateway:
+    def __init__(
+        self,
+        adapters: dict[str, ProviderAdapter],
+        ledger: LedgerSink,
+        resolver: Callable[[Tier], Route] = resolve_route,
+    ) -> None:
+        self._adapters = adapters
+        self._ledger = ledger
+        self._resolve = resolver
+
+    def _adapter_for(self, provider: str) -> ProviderAdapter:
+        adapter = self._adapters.get(provider)
+        if adapter is None:
+            raise AppError(ErrorCode.LLM_UNAVAILABLE, f"no adapter for provider {provider!r}")
+        return adapter
+
+    def _usage(self, route: Route, pu: ProviderUsage) -> Usage:
+        cost, currency = cost_minor(route.provider, route.model, pu.input_tokens, pu.output_tokens)
+        return Usage(
+            provider=route.provider,
+            model=route.model,
+            input_tokens=pu.input_tokens,
+            output_tokens=pu.output_tokens,
+            cache_read_tokens=pu.cache_read_tokens,
+            cost_minor=cost,
+            currency=currency,
+        )
+
+    def _log_call(self, req: LlmRequest, usage: Usage, *, stream: bool) -> None:
+        log.info(
+            "llm_call",
+            provider=usage.provider,
+            model=usage.model,
+            tier=req.tier,
+            input_tokens=usage.input_tokens,
+            output_tokens=usage.output_tokens,
+            cache_read_tokens=usage.cache_read_tokens,
+            cost_minor=usage.cost_minor,
+            currency=usage.currency,
+            stream=stream,
+            input_chars=_input_len(req),
+            project_id=str(req.scope.project_id) if req.scope.project_id else None,
+        )
+
+    async def run(self, req: LlmRequest) -> LlmResponse:
+        route = self._resolve(req.tier)
+        adapter = self._adapter_for(route.provider)
+        result = await adapter.complete(req, route.model)
+        usage = self._usage(route, result.usage)
+        await self._ledger.record(req.scope, usage)
+        self._log_call(req, usage, stream=False)
+        return LlmResponse(
+            text=result.text,
+            parsed=result.parsed,
+            usage=usage,
+            served_by=ServedBy(provider=route.provider, model=route.model),
+        )
+
+    async def stream(self, req: LlmRequest) -> AsyncIterator[Delta]:
+        route = self._resolve(req.tier)
+        adapter = self._adapter_for(route.provider)
+        final = ProviderUsage(input_tokens=0, output_tokens=0)
+        async for chunk in adapter.stream(req, route.model):
+            if chunk.text:
+                yield Delta(text=chunk.text)
+            if chunk.usage is not None:
+                final = chunk.usage
+        usage = self._usage(route, final)
+        await self._ledger.record(req.scope, usage)
+        self._log_call(req, usage, stream=True)