$props & $derived should use let instead of const about svelte HOT 3 CLOSED

This comes down to stylistic preference. I personally for example want to use const for components that only have readonly props. Or I prefer to use const for $derived because for me it better communicates that this is a readonly value, not necessarily that the value itself never changes.

We shouldn't be in the business of dictating these preferences, therefore closing.

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You think about it that way, I think about it completely different. For me it's that I as the user am not allowed to reassign the derived value / the prop, not that the value doesn't change.
So yes this is absolutely stylistic preferences.

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Javascript already has a muddy definition of const but the following should impossible in javascript with const

const { value } = $props()

console.log(value) // 1

function doSomethingLater{
    console.log(value) // 4
}

The const declaration creates an immutable reference to a value.
The variable identifier cannot be reassigned.
You should understand const declarations as "create a variable whose identity remains constant"

https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Statements/const

Silently converting the behavior of const to let for signals doesn't feel like a stylistic preference to me.

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