Record clean security workplan cutoff

Assistant: codex
Assistant-Model: gpt-5.6-sol
Assistant-Session: 01a0260c-4067-7052-9647-ad000d576e38

src/whitehat_security/engagement.py

@@ -37,6 +37,8 @@ class Engagement:
         return engagement
 
     def validate(self, *, now: datetime | None = None) -> None:
+        if self.raw.get("status") == "cancelled":
+            raise AuthorizationError("engagement is cancelled")
         current = now or datetime.now(UTC)
         start = _timestamp(self.raw["window_start"])
         end = _timestamp(self.raw["window_end"])