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/skills/learning/evidence.py

@@ -0,0 +1,76 @@
+"""Evidence selection for skill learning."""
+
+from __future__ import annotations
+
+from dataclasses import dataclass, field
+from typing import Any
+
+from beaver.engine.session.manager import SessionManager
+from beaver.memory.runs.store import RunMemoryStore
+
+
+@dataclass(slots=True)
+class EvidencePacket:
+    run_ids: list[str]
+    session_ids: list[str]
+    task_summaries: list[str]
+    session_excerpts: list[str]
+    metadata: dict[str, Any] = field(default_factory=dict)
+
+
+class EvidenceSelector:
+    def __init__(self, run_store: RunMemoryStore, session_manager: SessionManager | None = None) -> None:
+        self.run_store = run_store
+        self.session_manager = session_manager
+
+    def select_runs_for_revision(self, skill_name: str, version: str, limit: int = 5) -> list[str]:
+        runs = self.run_store.list_runs_by_skill(skill_name, version=version, limit=limit)
+        return [record.run_id for record in runs]
+
+    def select_runs_for_new_skill(self, theme: str, limit: int = 5) -> list[str]:
+        lowered = theme.lower().strip()
+        matches = []
+        for record in self.run_store.list_runs():
+            if lowered and lowered not in record.task_text.lower():
+                continue
+            matches.append(record.run_id)
+        return matches[-limit:]
+
+    def build_evidence_packet(self, run_ids: list[str], session_ids: list[str] | None = None) -> EvidencePacket:
+        runs_by_id = {record.run_id: record for record in self.run_store.list_runs()}
+        resolved_run_ids: list[str] = []
+        resolved_session_ids: list[str] = list(dict.fromkeys(session_ids or []))
+        task_summaries: list[str] = []
+        session_excerpts: list[str] = []
+        for run_id in run_ids:
+            record = runs_by_id.get(run_id)
+            if record is None:
+                continue
+            resolved_run_ids.append(run_id)
+            if record.session_id not in resolved_session_ids:
+                resolved_session_ids.append(record.session_id)
+            summary = record.task_text.strip()
+            if summary:
+                task_summaries.append(summary[:400])
+            if self.session_manager is not None:
+                excerpt = self._session_excerpt(record.session_id, run_id)
+                if excerpt:
+                    session_excerpts.append(excerpt)
+        return EvidencePacket(
+            run_ids=resolved_run_ids,
+            session_ids=resolved_session_ids,
+            task_summaries=task_summaries[:8],
+            session_excerpts=session_excerpts[:6],
+            metadata={"bounded": True},
+        )
+
+    def _session_excerpt(self, session_id: str, run_id: str) -> str:
+        if self.session_manager is None:
+            return ""
+        events = self.session_manager.get_run_event_records(session_id, run_id)
+        visible: list[str] = []
+        for event in events:
+            if not event.context_visible or not event.content:
+                continue
+            visible.append(f"{event.role}: {event.content.strip()}")
+        return "\n".join(visible[:12])[:2000]