refactor: 架构重组 — doc/bot → core/infra，新增 Agent 调度模块

- src/doc/ 拆分为 src/core/extraction/, matching/, validation/（核心业务逻辑）
- src/bot/ 重命名为 src/infra/browser/（浏览器自动化基础设施）
- fill_consumable_doc.py → src/infra/documents/consumable.py
- 新增 Agent 调度模块：coordinator.py, events.py, session.py，重构 orchestrator.py
- 更新 AGENTS.md、README.md 及所有子目录 README

src/agent/session.py

@@ -0,0 +1,101 @@
+"""Agent 会话管理
+
+负责会话状态的定义、序列化和持久化。
+"""
+
+from __future__ import annotations
+
+import json
+from dataclasses import asdict, dataclass, field
+from enum import StrEnum
+from pathlib import Path
+from typing import Any
+
+from .. import get_logger
+
+log = get_logger("agent.session")
+
+# ------------------------------------------------------------------
+# 状态枚举
+# ------------------------------------------------------------------
+
+
+class AgentState(StrEnum):
+    IDLE = "idle"
+    EXTRACTING = "extracting"
+    AWAITING_SUPPLEMENT = "awaiting_supplement"
+    READY = "ready"
+    SUBMITTING = "submitting"
+    DONE = "done"
+    ERROR = "error"
+
+
+# ------------------------------------------------------------------
+# Agent 会话数据模型
+# ------------------------------------------------------------------
+
+
+@dataclass
+class AgentSession:
+    """Agent 会话状态"""
+
+    session_id: str
+    state: AgentState = AgentState.IDLE
+    rounds: int = 0
+    max_rounds: int = 5
+    invoice_type: str = "travel"  # "travel" 或 "normal"
+    extracted_info: dict[str, Any] = field(default_factory=dict)
+    validation_reports: list[dict[str, Any]] = field(default_factory=list)
+    user_supplements: list[str] = field(default_factory=list)
+    error_message: str = ""
+
+    def to_dict(self) -> dict[str, Any]:
+        return asdict(self)
+
+    @classmethod
+    def from_dict(cls, data: dict[str, Any]) -> AgentSession:
+        # 兼容旧版本：state 可能是字符串
+        if "state" in data and isinstance(data["state"], str):
+            data["state"] = AgentState(data["state"])
+        return cls(**data)
+
+    def is_terminal(self) -> bool:
+        """判断会话是否处于终态（已提交或已完成）"""
+        return self.state in (AgentState.DONE, AgentState.SUBMITTING, AgentState.READY)
+
+
+# ------------------------------------------------------------------
+# 持久化
+# ------------------------------------------------------------------
+
+AGENT_STATE_FILE = "agent_state.json"
+
+
+def save_agent_state(session_dir: Path, session: AgentSession) -> None:
+    """将 Agent 会话状态持久化到 session 目录。"""
+    state_path = session_dir / AGENT_STATE_FILE
+    tmp_path = session_dir / (AGENT_STATE_FILE + ".tmp")
+    with open(tmp_path, "w", encoding="utf-8") as f:
+        json.dump(session.to_dict(), f, ensure_ascii=False, indent=2)
+    tmp_path.replace(state_path)
+
+
+def load_agent_state(session_dir: Path) -> AgentSession | None:
+    """从 session 目录加载 Agent 会话状态。"""
+    state_path = session_dir / AGENT_STATE_FILE
+    if not state_path.exists():
+        return None
+    try:
+        with open(state_path, encoding="utf-8") as f:
+            return AgentSession.from_dict(json.load(f))
+    except Exception as e:
+        log.warning("加载 Agent 状态失败: %s", e)
+        return None
+
+
+def create_agent_session(session_id: str, invoice_type: str = "travel") -> AgentSession:
+    """创建新的 Agent 会话。"""
+    return AgentSession(
+        session_id=session_id,
+        invoice_type=invoice_type,
+    )