pi: 档位判定 tool_call hook + 心跳报 native

- worker.mjs: mailContext 加 permissionMode 字段（从 SSE payload 读入）
- tool_call hook 增加档位判定：
  full → 不拦截任何工具（直接 return）
  plan → 被守卫工具（bash/write/edit）一律 block + 返回原因说明
  workspace → 走原有问人流程（不变）
- index.mjs 心跳上报 mode_enforcement: 'native'
- 导入 normalizeMode/MODE_FULL/MODE_PLAN 从 lib/permission-mode.js
- 377 测试全过

plugins/pi-mail-bridge/src/index.mjs

@@ -322,6 +322,7 @@ async function main() {
   const beat = async () => {
     const [platform_sessions, models] = await Promise.all([reportSessions(), reportModels()]);
     const body = {};
+    body.mode_enforcement = 'native'; // tool_call hook 能 block bash/write/edit
     if (platform_sessions) body.platform_sessions = platform_sessions;
     if (models) body.models = models;
     try {

plugins/pi-mail-bridge/src/worker.mjs

@@ -54,6 +54,7 @@ import { explicitSends, shouldSkipAutoRelay } from '../lib/relay-dedup.js';
 import { autoRelayDecision } from '../lib/relay-policy.js';
 import { adoptedSessionID, adoptMissingMessage } from '../lib/adopt.js';
 import { isApproval, isAlwaysDecision } from '../lib/permission-grants.js';
+import { normalizeMode, MODE_FULL, MODE_PLAN } from '../lib/permission-mode.js';
 import { clampRelayKey, isPermanentFailure } from '../lib/relay-key.js';
 
 // ─── 与主进程的通道 ───
@@ -90,7 +91,7 @@ let job = null;
 let client = null;
 let modelRuntime = null;
 let piSessionId = '';
-let mailContext = { replyTo: '', subject: '', mailID: '' };
+let mailContext = { replyTo: '', subject: '', mailID: '', permissionMode: 'workspace' };
 let lastSyncedName = '';
 let relayedKey = '';
 let finished = false;
@@ -110,6 +111,18 @@ function permissionExtension() {
 
   return (pi) => {
     pi.on('tool_call', async (event, ctx) => {
+      // ── 档位判定 ──
+      // plan:  被守卫的工具一律直接拒绝（该档语义是「不动手」，没什么可问人的）
+      // full:  不拦截（已声明全权）
+      // workspace: 走原有问人流程
+      const mode = normalizeMode(mailContext.permissionMode);
+      if (mode === MODE_FULL) return; // full 档不拦任何工具
+      if (mode === MODE_PLAN && GUARDED.has(event.toolName)) {
+        return {
+          block: true,
+          reason: `plan 档下不允许执行 ${event.toolName}。本档只允许读与查，请把方案写在回信里。如需动手请让发件人把档位改成 workspace。`,
+        };
+      }
       if (!GUARDED.has(event.toolName)) return;
 
       const sid = ctx?.sessionManager?.getSessionId?.() || '';
@@ -559,6 +572,7 @@ process.on('message', (msg) => {
       replyTo: msg.data?.from_name || '',
       subject: msg.data?.subject || '',
       mailID: msg.data?.mail_id || '',
+      permissionMode: msg.data?.permission_mode || 'workspace',
     };
     lastSyncedName = msg.lastSyncedName || '';
     for (const t of msg.grants || []) grants.add(t);