Flux can't change prompt during training

bmaltais says this is a problem in sd-scripts

Changing the prompt.txt during training produces the following message when the next sample point is reached, at which point it hangs. I like to change the prompt to see various aspects as the training proceeds, but can't with Flux loras.

(path)\venv\lib\site-packages\torch\utils\checkpoint.py:61: UserWarning: None of the inputs have requires_grad=True. Gradients will be None
warnings.warn(

Reproduce Flux LoRA training while changing prompt.txt before the next sample point, using the reported torch.utils.checkpoint.py warning as the initial symptom. Trace why training hangs after the prompt change; done means prompt updates take effect without the warning-induced hang.

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