While working on #18106 I noticed that we're not adding eager effects inside `mark_reactions` when `DEV` is `false`. As a result production build could have `$state.eager` or `$state.pending` not working correctly.

No test because I can't get Vitest to not run with `DEV` being `true`.

While working on #18106 I noticed that we're not adding eager effects
inside `mark_reactions` when `DEV` is `false`. As a result production
build could have `$state.eager` or `$state.pending` not working
correctly.

~No test because I can't get Vitest to not run with `DEV` being `true`.~
added a test

This PR was opened by the [Changesets
release](https://github.com/changesets/action) GitHub action. When
you're ready to do a release, you can merge this and the packages will
be published to npm automatically. If you're not ready to do a release
yet, that's fine, whenever you add more changesets to main, this PR will
be updated.


# Releases
## svelte@5.55.6

### Patch Changes

- fix: leave stale promises to wait for a later resolution, instead of
rejecting ([#18180](#18180))

- fix: keep dependencies of `$state.eager/pending`
([#18218](#18218))

- fix: reapply context after transforming error during SSR
([#18099](#18099))

- fix: don't rebase just-created batches
([#18117](#18117))

- chore: allow `null` for `pending` in typings
([#18201](#18201))

- fix: flush eager effects in production
([#18107](#18107))

- fix: rethrow error of failed iterable after calling `return()`
([#18169](#18169))

- fix: account for proxified instance when updating `bind:this`
([#18147](#18147))

- fix: ensure scheduled batch is flushed if not obsolete
([#18131](#18131))

- fix: resolve stale deriveds with latest value
([#18167](#18167))

- chore: remove unnecessary `increment_pending` calls
([#18183](#18183))

- fix: correctly compile component member expressions for SSR
([#18192](#18192))

- fix: reset `source.updated` stack traces after `flush`
([#18196](#18196))

- fix: replacing async 'blocking' strategy with 'merging'
([#18205](#18205))

- fix: allow `@debug` tags to reference awaited variables
([#18138](#18138))

- fix: re-run fallback props if dependencies update
([#18146](#18146))

- fix: abort running obsolete async branches
([#18118](#18118))

- fix: ignore comments when reading CSS values
([#18153](#18153))

- fix: wrap `Promise.all` in `save` during SSR
([#18178](#18178))

- fix: ignore false-positive errors of `$inspect` dependencies
([#18106](#18106))

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