[Medium] Race Condition in metamask-extension

## Bug Report

**Type**: Race Condition
**Severity**: Medium
**File**: src/concurrent/metamask-extension.go:189

### Description
多个线程同时访问共享变量时缺乏同步机制。

### Impact
可能导致数据不一致或程序崩溃。

### Proposed Fix
使用mutex保护共享变量。

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Automated Bug Report - 2026-02-05

Start by checking whether src/concurrent/metamask-extension.go:189 exists, then inspect the shared-variable access described in the report. Confirm the race condition and define completion as synchronized access with a regression check covering the affected behavior.

Written by the indexing model from the issue text.