The Dai token contract is immutable and was provided a chainId in its constructor.
The Dai permit derives the digest from the DOMAIN_SEPARATOR, which is based on the chainId provided in the constructor rather than the current chainId.
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Dai 代币合约是不可变的，并在其构造函数中提供了一个 chainId。
Dai 许可证从 DOMAIN_SEPARATOR 中派生摘要，该摘要基于构造函数中提供的chainId，而不是当前的chainId。
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