Svelte 5: next43 -> next44: can't convert symbol to string

[dm-de]

Describe the bug

Possible related to this: #10343

This adds new bug to Svelte 5

Reproduction

Click on any button - and you get many errors

See Item.svelte HTML comment. This line produce error.

LINK

Logs

Uncaught TypeError: can't convert symbol to string

readonly_error playground:output:335
proxy playground:output:86
set playground:output:241
foo playground:output:3415
batch_inspect playground:output:558
on_click playground:output:3370
handle_event_propagation playground:output:2279

System Info

running Svelte compiler version 5.0.0-next.44

Severity

blocking an upgrade

[evnix]

I upgraded from next.37 to next.59

and got the same error,

as mentioned, we can't do an upgrade