✨ feat: 阶段 0 收尾——认证边界、请求上下文与垂直切片（WP-01 第 5-7 步）

- 认证：Web Session（__Host- Cookie、HttpOnly/Secure/SameSite=Lax、CSPRNG opaque token 数据库只存哈希）、CSRF 双提交、Origin 校验、dev 登录/登出端点；未认证 401、缺 CSRF 403
- 中间件：Hunjing-Request-ID 回显/生成（request_ UUIDv4）+ W3C traceparent 校验透传；JSON 结构化日志与敏感头脱敏
- 迁移 2：conversation/branch/message/run/idempotency_record 五表（含检查约束与复合索引）；Session 补 token/csrf 哈希列
- 垂直切片：POST /v1/conversations/{id}/messages 按 Idempotency-Key 幂等（同键同体 200 重放、异体 409），同事务原子写 Message+Run+Audit+Outbox+幂等记录；ContentBlock text/markdown 判别联合（未知类型 422）
- SSE：GET /v1/runs/{id}/events 返回快照与终止状态事件 envelope
- 测试 26 项全绿：IDOR 跨域 404 fail-closed、失败注入回滚无孤儿（Run 崩溃后 message/run/audit/outbox/幂等全零）、SSE 事件序、auth 边界；ruff/mypy strict 干净
- 修复真实问题：asyncpg 跨事件循环（anyio/pytest-asyncio 双 loop、模块级 engine 改为 app 实例持有）、httpx 拒存 http 下 Secure Cookie

backend/app/conversations/schemas.py

@@ -0,0 +1,60 @@
+"""对话域 schema：ContentBlock 判别联合（垂直切片子集）。
+
+完整 21 类型随 WP-03 落地；本切片登记 text/markdown 并拒绝未知类型，
+契约真源为 openapi/openapi.yaml。
+"""
+
+from typing import Annotated, Literal
+
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class BlockBase(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    id: str | None = None  # 创建请求可省略，由服务端生成
+    status: Literal["pending", "streaming", "completed", "failed", "cancelled"] | None = None
+
+
+class TextBlock(BlockBase):
+    type: Literal["text"]
+    text: str
+    language: str | None = None
+
+
+class MarkdownBlock(BlockBase):
+    type: Literal["markdown"]
+    text: str
+    flavor: Literal["hunjing-gfm-v1"] = "hunjing-gfm-v1"
+
+
+ContentBlock = Annotated[TextBlock | MarkdownBlock, Field(discriminator="type")]
+
+
+class MessageIn(BaseModel):
+    model_config = ConfigDict(extra="forbid")
+
+    content: list[ContentBlock] = Field(min_length=1, max_length=64)
+    start_run: bool = True
+
+
+class MessageOut(BaseModel):
+    id: str
+    conversation_id: str
+    branch_id: str
+    role: str
+    content: list[dict[str, object]]
+    created_at: str
+
+
+class RunOut(BaseModel):
+    id: str
+    conversation_id: str | None
+    status: str
+    created_at: str
+    completed_at: str | None = None
+
+
+class MessageCreatedOut(BaseModel):
+    message: MessageOut
+    run: RunOut | None