MCP是手腳，Skill是靈魂· 第二篇:給Skill穿上鎧甲

# 脆弱版：沒有任何防禦
def process_github_issues(mcp_output):
 issues = mcp_output["data"]["issues"] # KeyError 風險
 for issue in issues:
 assignee = issue["assignee"]["login"] # assignee 可能是 null！
 priority = int(issue["labels"][0]["name"]) # labels 可能為空！
 if priority > 5:
 send_notification(assignee, issue["title"])

# 鎧甲版：先定義模型，再驗證
from pydantic import BaseModel, Field, validator
from typing import Optional, List

class GitHubIssue(BaseModel):
 id: int
 number: int
 title: str
 state: str = "open"
 assignee: Optional[GitHubUser] = None
 labels: List[GitHubLabel] = []
 @validator('state')
 def validate_state(cls, v):
 if v not in ['open', 'closed']:
 raise ValueError(f'Invalid state: {v}')
 return v
class GitHubIssueList(BaseModel):
 issues: List[GitHubIssue] = []
 total_count: int = 0
 page: int = 1
 has_more: bool = False

def process_github_issues(mcp_output):
 try:
 issue_list = GitHubIssueList(**mcp_output.get("data", {}))
 except ValidationError as e:
 logger.error(f"MCP 輸出格式異常: {e}")
 return ProcessResult(success=False, error=str(e))
 notifications_sent = []
 for issue in issue_list.issues:
 if issue.assignee is None: # 要先判斷，IDE 會提示
 continue
 priority_labels = [l for l in issue.labels if l.name.startswith("P")]
 if not priority_labels:
 continue
 send_notification(issue.assignee.login, issue.title)
 notifications_sent.append(issue.number)
 return ProcessResult(success=True, notifications_sent=notifications_sent, total_processed=len(issue_list.issues))

class MCPGuard:
 def __init__(self, strict_mode: bool = False):
 self.strict_mode = strict_mode
 def call(self, mcp_tool_func, output_model: Type[T], *args, **kwargs) -> "MCPCallResult[T]":
 start_time = time.time()
 try:
 raw_output = mcp_tool_func(*args, **kwargs)
 except Exception as e:
 return MCPCallResult(success=False, error=str(e), error_type="api_error", call_duration_ms=...)
 try:
 if isinstance(raw_output, dict):
 validated_data = output_model(**raw_output)
 elif isinstance(raw_output, list):
 validated_data = output_model(items=raw_output)
 else:
 validated_data = output_model.parse_raw(str(raw_output))
 return MCPCallResult(success=True, data=validated_data, call_duration_ms=...)
 except ValidationError as e:
 if self.strict_mode: raise
 return MCPCallResult(success=False, error=str(e), error_type="validation", raw_output=raw_output)
 def guarded(self, output_model: Type[T]):
 def decorator(func):
 @wraps(func)
 def wrapper(*args, **kwargs):
 return self.call(func, output_model, *args, **kwargs)
 return wrapper
 return decorator