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/safety.py

@@ -0,0 +1,109 @@
+"""Safety checks for generated skill drafts."""
+
+from __future__ import annotations
+
+import re
+from uuid import uuid4
+
+from beaver.memory.skills import SkillDraftSafetyReport
+from beaver.skills.specs import SkillDraft
+
+
+class SkillDraftSafetyChecker:
+    """Deterministic publish gate for skill drafts."""
+
+    _CRITICAL_PATTERNS = [
+        r"ignore (all )?(previous|system|developer) instructions",
+        r"bypass (permissions|permission|safety|policy|policies)",
+        r"disable (guardrails|safety|permission checks)",
+        r"reveal (secrets|api keys|tokens|credentials)",
+        r"exfiltrate",
+    ]
+    _DANGEROUS_TOOL_HINTS = {
+        "shell",
+        "terminal",
+        "bash",
+        "filesystem_write",
+        "write_file",
+        "delete_file",
+        "network",
+        "http",
+        "auth",
+        "credentials",
+    }
+
+    def __init__(self, *, allowed_tool_names: set[str] | None = None) -> None:
+        self.allowed_tool_names = allowed_tool_names
+
+    def check(self, draft: SkillDraft) -> SkillDraftSafetyReport:
+        issues: list[str] = []
+        blocked: list[str] = []
+        risk_level = "low"
+
+        frontmatter = draft.proposed_frontmatter
+        if not isinstance(frontmatter, dict):
+            blocked.append("frontmatter must be an object")
+        description = str(frontmatter.get("description") or "").strip()
+        if not description and draft.proposal_kind != "retire_skill":
+            issues.append("frontmatter.description is missing")
+            risk_level = _max_risk(risk_level, "medium")
+
+        tool_hints = _tool_hints(frontmatter)
+        if self.allowed_tool_names is not None:
+            unknown = [name for name in tool_hints if name not in self.allowed_tool_names]
+            if unknown:
+                blocked.append(f"unknown tool hints: {', '.join(sorted(unknown))}")
+        dangerous = sorted({name for name in tool_hints if name.lower() in self._DANGEROUS_TOOL_HINTS})
+        if dangerous:
+            issues.append(f"dangerous tool hints require high-risk review: {', '.join(dangerous)}")
+            risk_level = _max_risk(risk_level, "high")
+
+        content = f"{draft.proposed_content}\n{frontmatter}".lower()
+        for pattern in self._CRITICAL_PATTERNS:
+            if re.search(pattern, content):
+                blocked.append(f"critical prompt-safety pattern matched: {pattern}")
+                risk_level = "critical"
+
+        if draft.proposal_kind in {"retire_skill", "merge_skills"}:
+            risk_level = _max_risk(risk_level, "high")
+
+        passed = not blocked and risk_level != "critical"
+        return SkillDraftSafetyReport(
+            report_id=uuid4().hex,
+            skill_name=draft.skill_name,
+            draft_id=draft.draft_id,
+            passed=passed,
+            risk_level=risk_level,
+            issues=issues,
+            blocked_reasons=blocked,
+            suggested_fix=_suggest_fix(blocked, issues),
+            created_at=_utc_now(),
+        )
+
+
+def _tool_hints(frontmatter: dict) -> list[str]:
+    raw = frontmatter.get("tools")
+    if isinstance(raw, list):
+        return [str(item).strip() for item in raw if str(item).strip()]
+    if isinstance(raw, str):
+        return [item.strip() for item in raw.split(",") if item.strip()]
+    return []
+
+
+def _max_risk(left: str, right: str) -> str:
+    order = {"low": 0, "medium": 1, "high": 2, "critical": 3}
+    return left if order[left] >= order[right] else right
+
+
+def _suggest_fix(blocked: list[str], issues: list[str]) -> str:
+    if blocked:
+        return "Remove blocked instructions or invalid tool hints before review."
+    if issues:
+        return "Review the flagged issues before publishing."
+    return ""
+
+
+def _utc_now() -> str:
+    from datetime import datetime, timezone
+
+    return datetime.now(timezone.utc).isoformat()