feat(engine): 添加运行时上下文支持并重构工具迭代限制

添加 RuntimeContext 类用于捕获模型运行时的日期时间信息，
包括UTC时间、本地时间和时区信息，并在系统提示中显示这些信息。

同时增加最大上下文消息数和工具迭代次数的配置选项，
将验证服务从引擎加载器中移除，并更新相关的数据结构和接口。

BREAKING CHANGE: 移除了验证服务，相关字段被替换为证据状态和接受状态。

- 添加 RuntimeContext 类和相关渲染方法
- 增加 max_context_messages 和 max_tool_iterations 配置
- 移除 ValidationService 相关代码
- 更新消息记录中的验证状态字段
- 添加原始工具调用检测和回退处理

app-instance/backend/beaver/engine/loader.py

@@ -24,7 +24,7 @@ from beaver.skills.learning.eval import SkillDraftEvaluator
 from beaver.skills.publisher import SkillPublisher
 from beaver.skills.reviews import ReviewService
 from beaver.skills.specs import SkillSpecStore
-from beaver.tasks import TaskExecutionPlanner, TaskService, ValidationService
+from beaver.tasks import TaskExecutionPlanner, TaskService
 from beaver.tasks.skill_resolver import TaskSkillResolver
 from beaver.skills import SkillAssembler, SkillsLoader
 from beaver.tools import ObjectBackedTool, ToolAssembler, ToolExecutor, ToolRegistry
@@ -91,7 +91,6 @@ class EngineLoadResult:
     task_skill_resolver: TaskSkillResolver | None = None
     task_service: TaskService | None = None
     task_execution_planner: TaskExecutionPlanner | None = None
-    validation_service: ValidationService | None = None
     mcp_manager: MCPConnectionManager | None = None
     mcp_report: dict[str, dict] = field(default_factory=dict)
     closeables: list[tuple[str, Callable[[], None]]] = field(default_factory=list, repr=False)
@@ -166,7 +165,6 @@ class EngineLoader:
         task_skill_resolver: TaskSkillResolver | None = None,
         task_service: TaskService | None = None,
         task_execution_planner: TaskExecutionPlanner | None = None,
-        validation_service: ValidationService | None = None,
     ) -> None:
         self.config = config or load_config(workspace=workspace, config_path=config_path)
         configured_workspace = self.config.agents_defaults.workspace
@@ -192,7 +190,6 @@ class EngineLoader:
         self._task_skill_resolver = task_skill_resolver
         self._task_service = task_service
         self._task_execution_planner = task_execution_planner
-        self._validation_service = validation_service
 
     def load(self) -> EngineLoadResult:
         """装配当前主链需要的最小 runtime 对象。"""
@@ -276,7 +273,6 @@ class EngineLoader:
         )
         task_service = self._task_service or TaskService(workspace / "tasks")
         task_execution_planner = self._task_execution_planner or TaskExecutionPlanner(task_skill_resolver=task_skill_resolver)
-        validation_service = self._validation_service or ValidationService()
         mcp_manager = MCPConnectionManager(
             self.config.tools.mcp_servers,
             authz_config=self.config.authz,
@@ -311,7 +307,6 @@ class EngineLoader:
             task_skill_resolver=task_skill_resolver,
             task_service=task_service,
             task_execution_planner=task_execution_planner,
-            validation_service=validation_service,
             mcp_manager=mcp_manager,
         )
         if self._session_manager is None: