Tool Permission System Design

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)

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 }

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

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}` }
}

// 工厂函数用 TOOL_DEFAULTS 填充未声明的属性
const TOOL_DEFAULTS = {
  isEnabled:         () => true,
  isConcurrencySafe: () => false,   // 默认不并发（怕数据竞争）
  isReadOnly:        () => false,   // 默认假设会写入
  isDestructive:     () => false,   // 默认假设不可逆操作要谨慎
  checkPermissions:  (input) => ({ behavior: 'allow', updatedInput: input }), // 默认交给中央权限系统
}
function buildTool(def) { return { ...TOOL_DEFAULTS, ...def } }

class MyTool implements Tool {
  isReadOnly = () => false
  isConcurrencySafe = () => false

  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（命中后 type:'safetyCheck' → bypass 也拦不住，见下方说明）
    if (isDangerousPath(input.path)) {
      return {
        behavior: 'ask',
        message: '...',
        decisionReason: { type: 'safetyCheck', reason: '...', classifierApprovable: false }
      }
    }

    return { behavior: 'passthrough', message: '...' }  // 没意见 → 交给外层
  }
}

// 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" }]
    }]
  }
}

// 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
  )
}

// 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
}