Tool Permission System

Core Idea

Every time an agent calls a tool, a permission pipeline runs before execution. This pipeline is the single place that decides: auto-allow, ask the user, or deny. The pipeline is layered — different stakeholders (enterprise admin, user, project team, session) can each contribute rules, with higher layers overriding lower ones.

Tool call request
  ↓
[硬否决] Deny rules → immediate deny
  ↓
[强制确认] Ask rules → force prompt (even in bypass mode)
  ↓
[工具自身] Tool's checkPermissions() → tool-specific logic
  ↓
[安全绕过免疫] Safety checks (.git/, .claude/, shell configs) → prompt, immune to bypass
  ↓
[模式快速通过] Bypass / acceptEdits mode → immediate allow
  ↓
[白名单] Allow rules → immediate allow
  ↓
[默认] passthrough → prompt user (ask)

外层包装（作用于整条流水线之后）：

• dontAsk 模式：把所有 ask 转为 deny（用于无交互的后台 agent）
• auto 模式：把所有 ask 转给 AI 分类器判断，而不是打断用户
• headless 模式：先跑 PermissionRequest hooks，hooks 没回应就自动 deny

Workflow

1. 定义三种决策行为

type PermissionBehavior = 'allow' | 'deny' | 'ask'

type PermissionDecision =
  | { behavior: 'allow'; updatedInput?: unknown; decisionReason?: DecisionReason }
  | { behavior: 'ask';   message: string; suggestions?: PermissionUpdate[] }
  | { behavior: 'deny';  message: string; decisionReason: DecisionReason }

2. 建立分层规则来源

规则来源按优先级从高到低排列：

policySettings    ← 企业管理员，用户不可覆盖
userSettings      ← 用户全局 (~/.agent/settings.json)
projectSettings   ← 项目级 (.agent/settings.json，可提交 git)
localSettings     ← 本地私有 (.agent/settings.local.json)
cliArg            ← 启动参数
command           ← 运行时命令
session           ← 当次会话临时

每条规则的格式：ToolName 或 ToolName(content)。

3. 实现权限决策函数

async function hasPermission(tool, input, context): Promise<PermissionDecision> {
  // Step 1: deny rules (优先级最高，含企业强制)
  const denyRule = findMatchingRule(context.denyRules, tool, input)
  if (denyRule) return { behavior: 'deny', message: '...', decisionReason: { type: 'rule', rule: denyRule } }

  // Step 2: ask rules (强制弹框，绕过模式也无法跳过)
  const askRule = findMatchingRule(context.askRules, tool, input)
  if (askRule) return { behavior: 'ask', message: '...' }

  // Step 3: 工具自身的 checkPermissions()
  const toolResult = await tool.checkPermissions(input, context)
  if (toolResult.behavior === 'deny') return toolResult
  if (toolResult.behavior === 'ask' && toolResult.decisionReason?.type === 'rule') return toolResult  // ask rule 免疫 bypass
  if (toolResult.behavior === 'ask' && toolResult.decisionReason?.type === 'safetyCheck') return toolResult  // 安全检查免疫 bypass

  // Step 4: bypass 模式快速通过
  if (context.mode === 'bypassPermissions') return { behavior: 'allow', updatedInput: input }

  // Step 5: allow rules 白名单
  const allowRule = findMatchingRule(context.allowRules, tool, input)
  if (allowRule) return { behavior: 'allow', updatedInput: input }

  // Step 6: 默认转 ask
  return { behavior: 'ask', message: `Agent requested to use ${tool.name}` }
}

4. 为每个工具实现 checkPermissions()

每个工具可以有自己的内部权限逻辑：

class MyTool implements Tool {
  async checkPermissions(input, context): Promise<PermissionResult> {
    // 检查工具特定规则（如 Bash 检查具体命令前缀）
    const allowRules = getRuleContentsForTool(context, this, 'allow')
    if (allowRules.has(getCommandPrefix(input.command))) {
      return { behavior: 'allow' }
    }

    // 检查危险路径
    if (isDangerousPath(input.path)) {
      return {
        behavior: 'ask',
        message: '...',
        decisionReason: { type: 'safetyCheck', reason: '...', classifierApprovable: false }
      }
    }

    return { behavior: 'passthrough', message: '...' }
  }
}

5. 实现 Hook 系统（可选但推荐）

Hook 让用户/企业在工具生命周期各节点插入自定义逻辑：

// 配置格式（settings.json）
{
  "hooks": {
    "PreToolUse": [{
      "matcher": "MyTool",          // 可选，工具名过滤
      "hooks": [{
        "type": "command",          // command | prompt | agent | http
        "command": "check-safety.sh $TOOL_INPUT"
      }]
    }],
    "PostToolUse": [{
      "matcher": "FileEdit",
      "hooks": [{ "type": "command", "command": "prettier --write $FILE_PATH" }]
    }]
  }
}

Hook 执行结果影响权限决策：

• exit 0 → 通过
• exit 2 → block（工具不执行）
• stdout 包含 JSON {"action": "allow"} → 覆盖决策

6. 实现 Denial 追踪（AI 分类器场景）

当使用 AI 分类器自动判断权限时，需要 circuit breaker 防止分类器过于严格：

// 连续拒绝 3 次或累计拒绝 20 次 → 回退到人工确认
const DENIAL_LIMITS = { maxConsecutive: 3, maxTotal: 20 }

function shouldFallback(state: DenialTrackingState): boolean {
  return (
    state.consecutiveDenials >= DENIAL_LIMITS.maxConsecutive ||
    state.totalDenials >= DENIAL_LIMITS.maxTotal
  )
}

Required Decisions

设计时必须明确的三个问题：

1. 哪些操作永远不需要确认？ → 放入 allow rules（如只读操作）
2. 哪些操作永远需要确认，不可绕过？ → 用 decisionReason.type === 'safetyCheck' 标记
3. 无人值守场景（CI/后台 agent）怎么处理？ → shouldAvoidPermissionPrompts = true + 跑 hooks + 自动 deny

Minimal Pattern

// 最简实现：三层规则 + 工具自检
type Rule = { toolName: string; content?: string; behavior: 'allow' | 'deny' | 'ask' }

type PermissionContext = {
  mode: 'default' | 'bypassPermissions' | 'acceptEdits'
  allowRules: Rule[]
  denyRules: Rule[]
  askRules: Rule[]
}

async function checkPermission(toolName: string, input: unknown, ctx: PermissionContext) {
  if (ctx.denyRules.some(r => matches(r, toolName, input))) return 'deny'
  if (ctx.askRules.some(r => matches(r, toolName, input))) return 'ask'
  if (ctx.mode === 'bypassPermissions') return 'allow'
  if (ctx.allowRules.some(r => matches(r, toolName, input))) return 'allow'
  return 'ask'  // default: prompt
}

Boundaries

This skill owns:

• 权限决策流水线的设计与实现
• 分层规则来源（policySettings → session）的优先级架构
• 工具级 checkPermissions() 接口设计
• Hook 系统的配置格式和生命周期事件
• AI 分类器 + Denial 追踪的 circuit breaker 模式
• 危险操作硬编码黑名单的设计原则

This skill does not own:

• 具体工具的业务逻辑（只关注权限接口）
• UI 确认弹框的实现（只关注决策结果）
• 用户认证/身份校验（不同于工具权限）
• AI 分类器的具体 prompt 工程

When More Detail Is Needed

• 完整 TypeScript 类型定义 → references/permission-types.ts
• 决策流水线带注释的详细实现 → references/permission-pipeline.md
• Denial 追踪 circuit breaker 完整代码 → references/denial-tracking.ts
• Hook 系统架构与所有事件类型 → references/hook-system.md
• settings.json 配置完整示例 → references/settings-examples.json