feat(beaver): 完成Task Team功能v1实现，重构后端架构支持统一内核

新增内部Task系统，包括验证、反馈门控机制，实现自动质量验证
(通过率>=0.75)和用户反馈闭环(satisfied/revise/abandon)。

实现Agent Team v1协调器，支持sequence/parallel/dag执行策略，
sub-agent复用主AgentLoop，每个run使用独立memory snapshot。

建立Skill学习pipeline，包含draft/审核/发布/回滚完整生命周期，
通过Task验证通过且用户满意才生成学习候选。

重构目录结构，移除third_party依赖，建立统一engine内核，
所有agent共享运行时基础组件。

更新ContextBuilder清理provider消息字段，增强SkillContext版本管理，
集成TaskExecutionPlanner和TaskSkillResolver实现技能解析机制。

app-instance/backend/beaver/tasks/service.py

@@ -0,0 +1,167 @@
+"""Internal service for automatic Task mode."""
+
+from __future__ import annotations
+
+from datetime import datetime, timezone
+from pathlib import Path
+from typing import Any
+from uuid import uuid4
+
+from .models import TaskEvent, TaskRecord, ValidationResult
+from .store import TaskStore
+
+
+class TaskService:
+    def __init__(self, root: str | Path) -> None:
+        self.store = TaskStore(root)
+
+    def create_task(
+        self,
+        *,
+        session_id: str,
+        description: str,
+        creator: str = "main-agent",
+        metadata: dict[str, Any] | None = None,
+    ) -> TaskRecord:
+        now = self._now()
+        task = TaskRecord(
+            task_id=uuid4().hex,
+            session_id=session_id,
+            description=description,
+            goal=description,
+            constraints=[],
+            priority=0,
+            status="open",
+            creator=creator,
+            created_at=now,
+            updated_at=now,
+            metadata=dict(metadata or {}),
+        )
+        self.store.upsert_task(task)
+        self._event(task, "created", payload={"description": description})
+        return task
+
+    def get_task(self, task_id: str) -> TaskRecord | None:
+        return self.store.get_task(task_id)
+
+    def get_task_by_run_id(self, run_id: str) -> TaskRecord | None:
+        return self.store.get_task_by_run_id(run_id)
+
+    def get_latest_open_task(self, session_id: str) -> TaskRecord | None:
+        return self.store.get_latest_open_task(session_id)
+
+    def start_run(self, task_id: str, *, user_message: str, attempt_index: int) -> TaskRecord:
+        task = self._require(task_id)
+        task.status = "running"
+        task.updated_at = self._now()
+        task.metadata["latest_user_message"] = user_message
+        task.metadata["latest_attempt_index"] = attempt_index
+        self.store.upsert_task(task)
+        self._event(task, "run_started", payload={"user_message": user_message, "attempt_index": attempt_index})
+        return task
+
+    def append_run(self, task_id: str, run_id: str, *, skill_names: list[str] | None = None) -> TaskRecord:
+        task = self._require(task_id)
+        if run_id not in task.run_ids:
+            task.run_ids.append(run_id)
+        for name in skill_names or []:
+            if name not in task.skill_names:
+                task.skill_names.append(name)
+        task.updated_at = self._now()
+        self.store.upsert_task(task)
+        self._event(task, "run_completed", run_id=run_id, payload={"skill_names": skill_names or []})
+        return task
+
+    def record_validation(self, task_id: str, run_id: str, validation: ValidationResult) -> TaskRecord:
+        task = self._require(task_id)
+        task.status = "awaiting_feedback"
+        task.updated_at = self._now()
+        task.validation_result = validation.to_dict()
+        self.store.upsert_task(task)
+        self._event(task, "validated", run_id=run_id, payload=validation.to_dict())
+        return task
+
+    def add_feedback(
+        self,
+        task_id: str,
+        *,
+        feedback_type: str,
+        comment: str | None = None,
+        run_id: str | None = None,
+    ) -> TaskRecord:
+        task = self._require(task_id)
+        now = self._now()
+        matching_feedback = any(
+            item.get("run_id") == run_id and item.get("feedback_type") == feedback_type
+            for item in task.feedback
+        )
+        conflicting_feedback = next(
+            (
+                item
+                for item in task.feedback
+                if item.get("run_id") == run_id and item.get("feedback_type") != feedback_type
+            ),
+            None,
+        )
+        if conflicting_feedback is not None:
+            raise ValueError(
+                f"Feedback for run_id={run_id!r} was already recorded as "
+                f"{conflicting_feedback.get('feedback_type')!r}"
+            )
+        if task.status in {"closed", "abandoned"} and not matching_feedback:
+            raise ValueError(f"Task {task.task_id} is already finalized as {task.status!r}")
+        if matching_feedback:
+            return task
+
+        entry = {
+            "feedback_type": feedback_type,
+            "comment": comment or "",
+            "run_id": run_id,
+            "created_at": now,
+        }
+        task.feedback.append(entry)
+        if feedback_type == "revise":
+            task.status = "needs_revision"
+        elif feedback_type == "abandon":
+            task.status = "abandoned"
+            task.closed_at = now
+            task.close_reason = comment or "abandoned"
+        elif feedback_type == "satisfied":
+            task.status = "closed"
+            task.closed_at = now
+            task.close_reason = "satisfied"
+            task.satisfaction = 1.0
+        task.updated_at = now
+        self.store.upsert_task(task)
+        self._event(task, f"feedback_{feedback_type}", run_id=run_id, payload=entry)
+        return task
+
+    def _require(self, task_id: str) -> TaskRecord:
+        task = self.store.get_task(task_id)
+        if task is None:
+            raise ValueError(f"Unknown task_id: {task_id}")
+        return task
+
+    def _event(
+        self,
+        task: TaskRecord,
+        event_type: str,
+        *,
+        run_id: str | None = None,
+        payload: dict[str, Any] | None = None,
+    ) -> None:
+        self.store.append_event(
+            TaskEvent(
+                event_id=uuid4().hex,
+                task_id=task.task_id,
+                session_id=task.session_id,
+                run_id=run_id,
+                event_type=event_type,
+                created_at=self._now(),
+                payload=dict(payload or {}),
+            )
+        )
+
+    @staticmethod
+    def _now() -> str:
+        return datetime.now(timezone.utc).isoformat()