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/checkpoint_routes.py

@@ -12,7 +12,9 @@ from typing import Optional
 from src.blackboard.operations import Blackboard
 from src.utils import get_data_root
 
-router = APIRouter(prefix="/api/projects/{project_id}/tasks/{task_id}/checkpoints", tags=["checkpoints"])
+router = APIRouter(
+    prefix="/api/projects/{project_id}/tasks/{task_id}/checkpoints",
+    tags=["checkpoints"])
 
 
 # ── 请求模型 ──
@@ -50,10 +52,12 @@ def list_checkpoints(project_id: str, task_id: str):
 
 
 @router.post("")
-def create_checkpoint(project_id: str, task_id: str, req: CreateCheckpointRequest):
+def create_checkpoint(project_id: str, task_id: str,
+                      req: CreateCheckpointRequest):
     """Agent 创建 checkpoint"""
     if req.type not in ("verify", "decision", "action"):
-        raise HTTPException(status_code=400, detail=f"Invalid checkpoint type: {req.type}")
+        raise HTTPException(status_code=400,
+                            detail=f"Invalid checkpoint type: {req.type}")
 
     bb = _bb(project_id)
     # 验证 task 存在
@@ -73,10 +77,15 @@ def create_checkpoint(project_id: str, task_id: str, req: CreateCheckpointReques
 
 
 @router.post("/{checkpoint_id}/approve")
-def approve_checkpoint(project_id: str, task_id: str, checkpoint_id: str, req: ResolveCheckpointRequest):
+def approve_checkpoint(project_id: str, task_id: str,
+                       checkpoint_id: str, req: ResolveCheckpointRequest):
     """用户通过 checkpoint → 自动推进 task 状态"""
     bb = _bb(project_id)
-    result = bb.resolve_checkpoint(checkpoint_id, "approve", req.resolved_by, req.note)
+    result = bb.resolve_checkpoint(
+        checkpoint_id,
+        "approve",
+        req.resolved_by,
+        req.note)
     if result is None:
         raise HTTPException(status_code=404, detail="Checkpoint not found")
     if "error" in result:
@@ -97,10 +106,15 @@ def approve_checkpoint(project_id: str, task_id: str, checkpoint_id: str, req: R
 
 
 @router.post("/{checkpoint_id}/reject")
-def reject_checkpoint(project_id: str, task_id: str, checkpoint_id: str, req: ResolveCheckpointRequest):
+def reject_checkpoint(project_id: str, task_id: str,
+                      checkpoint_id: str, req: ResolveCheckpointRequest):
     """用户驳回 checkpoint → task 回到 working"""
     bb = _bb(project_id)
-    result = bb.resolve_checkpoint(checkpoint_id, "reject", req.resolved_by, req.note)
+    result = bb.resolve_checkpoint(
+        checkpoint_id,
+        "reject",
+        req.resolved_by,
+        req.note)
     if result is None:
         raise HTTPException(status_code=404, detail="Checkpoint not found")
     if "error" in result: