[Bug] Update weights from disk ends in runtime corruption for different size model

[zhaochenyang20]

Checklist

• 1. I have searched related issues but cannot get the expected help.
• 2. The bug has not been fixed in the latest version.
• 3. Please note that if the bug-related issue you submitted lacks corresponding environment info and a minimal reproducible demo, it will be challenging for us to reproduce and resolve the issue, reducing the likelihood of receiving feedback.
• 4. If the issue you raised is not a bug but a question, please raise a discussion at https://github.com/sgl-project/sglang/discussions/new/choose Otherwise, it will be closed.
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Describe the bug

In our unit test test_update_weights_from_disk.py, we only test the update of the Engine with a wrong model name. But if you update llama 3.2 1B with llama 3.2 3B, the engine will be corrupted. This is found in our document native_api.ipynb. I now change our native_api.ipynb to be the same as our unit test. But I fix the error of updating weights from disk with a model of a different size.

Reproduction

Easy to reproduce.

Environment

Easy to say.

[zhaochenyang20]

This should not be closed since this bug is not fixed right now.