Reactivity regression since 5.39.0

[Conduitry]

Describe the bug

I have a pattern for trying to deal with async data that isn't working properly anymore since 5.39.0. $inspect(delayed_value) shows that delayed_value is getting updated, but this is not reflected in the DOM.

The $derived on line 8 looks useless, but it is part of what makes this break, and it was part of a more complicated expression in my original app that did actually do something.

Apart from any runtime changes in 5.39.0, the compilation change that I'm seeing since 5.38.10 is await null; starting to get compiled to (await $.save(null))();.

Reproduction

https://svelte.dev/playground/hello-world?version=5.39.3#H4sIAAAAAAAACnWR3WoDIRSEX0VkIS6U9H6bFHrXd2hKsOvYCqe66NlNw5J3r2ZtQ_pzI_iNc2Y4ztLrd8hOPoIoiEOIZISCcQzTyhtpHSHJ7mmWfBzKuwIyr66HYVinCcSFveiEv3gfPMNzHiM3qY9u4Pud33HGiUVECjRBbIUdfS-292Iu4o4JLPoxxuzMYpNYM1R7t4gNrEXP6yFCqba4ilu1a36DV5OmEQVe_GfUftkjeIxeLM766Cydyvnd7RW8NyB9hNnXmaIxiG6CUbW40umYey-janV90I6FH4mu81Y2hNWSU6ssOf9m_Cqgqq9xPg15AepKLdrm9rJiP5dPC_Y64JT5T5B_ifHBsuOY78_5ph0dnDeys5oSTp-3GN7uKAIAAA

Logs

init undefined
update foo

System Info

REPL

Severity

blocking an upgrade

[dummdidumm]

This was fixed at some point