fix(lint): 修复 PR #14 引入的 lint 回退 (119→0)

PR #14 从旧分支复制文件导致回退了 PR #10 的 lint 修复。
修复内容:
- autoflake 移除未使用导入/变量
- autopep8 修复缩进/空格
- 手动修复 F821(pathlib→Path), F541(f-string), F841(未使用变量)
- 所有修复均通过 flake8 --max-line-length=120 --extend-ignore=E501 检查 (0 errors)

src/api/mail_routes.py

@@ -9,7 +9,7 @@ from __future__ import annotations
 import json
 from datetime import datetime
 from pathlib import Path
-from typing import Any, Dict, List, Optional
+from typing import Any, Dict, Optional
 
 from fastapi import APIRouter, HTTPException, Query
 
@@ -34,7 +34,9 @@ def _get_valid_agents() -> set:
         except Exception:
             pass
     # fallback：硬编码
-    return {"zhangfei-dev", "guanyu-dev", "zhaoyun-data", "jiangwei-infra", "pangtong-fujunshi", "simayi-challenger"}
+    return {"zhangfei-dev", "guanyu-dev", "zhaoyun-data",
+            "jiangwei-infra", "pangtong-fujunshi", "simayi-challenger"}
+
 
 router = APIRouter(prefix="/api/mail", tags=["mail"])
 
@@ -97,7 +99,10 @@ async def list_mail(
 ):
     """Mail 列表（按时间倒序）"""
     bb = _bb()
-    tasks = bb.list_tasks(status=status, assignee=to_agent, assigned_by=from_agent)
+    tasks = bb.list_tasks(
+        status=status,
+        assignee=to_agent,
+        assigned_by=from_agent)
 
     mails = []
     for t in tasks:
@@ -222,13 +227,16 @@ async def send_mail(body: Dict[str, Any]):
 
         # A8: 只有原邮件的双方能回复（严格 1 对 1）
         if from_agent not in (orig_from, orig_to):
-            raise HTTPException(400, f"只有邮件的发送者或接收者可以回复")
+            raise HTTPException(400, "只有邮件的发送者或接收者可以回复")
 
         # A6/A7: 自动纠正 to → 原邮件发件者
         to_agent = body.get("to", "").strip()
         corrected_to = orig_from  # 回复方向固定: reply → original sender
         if to_agent and to_agent != corrected_to:
-            auto_corrected = {"field": "to", "original": to_agent, "corrected": corrected_to}
+            auto_corrected = {
+                "field": "to",
+                "original": to_agent,
+                "corrected": corrected_to}
         to_agent = corrected_to
     else:
         # --- A2: to 必填（非回复场景） ---
@@ -255,7 +263,8 @@ async def send_mail(body: Dict[str, Any]):
     conversation_id = body.get("conversation_id")
     if not conversation_id and original:
         try:
-            orig_meta = json.loads(original.must_haves) if original.must_haves else {}
+            orig_meta = json.loads(
+                original.must_haves) if original.must_haves else {}
             conversation_id = orig_meta.get("conversation_id")
         except Exception:
             pass
@@ -310,10 +319,12 @@ async def delete_mail(prefix: Optional[str] = Query(None)):
     for t in tasks:
         if t.title and t.title.startswith(prefix):
             if t.status not in ("cancelled",):
-                bb.update_task_status(t.id, "cancelled", agent="mail-cleanup-api")
+                bb.update_task_status(
+                    t.id, "cancelled", agent="mail-cleanup-api")
                 deleted_ids.append(t.id)
 
-    return {"ok": True, "deleted_count": len(deleted_ids), "deleted_ids": deleted_ids}
+    return {"ok": True, "deleted_count": len(
+        deleted_ids), "deleted_ids": deleted_ids}
 
 
 @router.patch("/{mail_id}")