Store updates break transitions and components

Describe the bug Components with an out:[transition] and a store subscription don’t get destroyed if the store is updated while out:[transition] is in progress.

To Reproduce https://svelte.dev/repl/00d38994d0364ea3a3ae629937142ea6?version=3.12.1

1. Create a store
2. Subscribe to it in component A
3. Create an element with out:fade in component A
4. Destroy component A and trigger a store update before the animation has completed Result: component A never got destroyed.

Expected behavior Components should be destroyed

Severity Very. It breaks apps without a single warning or error. This means that the more complex/nested your app is, the harder it is to troubleshoot.

Additional context Any app that relies on URL params to update the store is highly susceptible to this bug. I ran into it with Sapper as well.

[Conduitry]

Fixed in 3.21.0 - https://svelte.dev/repl/00d38994d0364ea3a3ae629937142ea6?version=3.21.0

[jhwheeler]

Fixed in 3.21.0 - https://svelte.dev/repl/00d38994d0364ea3a3ae629937142ea6?version=3.21.0

not really fixed, if the duration of transition for out:send is more than 100ms it will likely to stuck again, if duration is 600ms or 1000ms… it will surely stuck.

I can confirm this is still an issue as described, except the threshold I found was 240ms. Anything above that and this bug occurs; 240ms or below, it works as expected.

Here you can see an example REPL: https://svelte.dev/repl/c2ec0888fcf044f78b0ab05c446d5787?version=3.24.1