fix(db): prevent cross-query data contamination in useLiveInfiniteQuery

[melvinhagberg]

When using useLiveInfiniteQuery with syncMode: 'on-demand', navigating between different queries on the same collection causes the wrong data to appear on the first page.

This happens because a new subscription's first snapshot reads from the local index, which may contain data loaded by a different subscription's loadSubset call.

The fix tracks whether loadSubset has been called on a collection. When a new subscription's first snapshot runs:

• If loadSubset has never been called, local data is from initial sync (valid for all queries)
• If loadSubset has been called, local data may be contaminated, so we skip local reads and let loadSubset provide the correct data

🎯 Changes

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested this code locally with pnpm test:pr.

🚀 Release Impact

• This change affects published code, and I have generated a changeset.
• This change is docs/CI/dev-only (no release).

[changeset-bot]

🦋 Changeset detected

Latest commit: c2b7c80

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 12 packages

Name	Type
@tanstack/db	Patch
@tanstack/angular-db	Patch
@tanstack/electric-db-collection	Patch
@tanstack/offline-transactions	Patch
@tanstack/powersync-db-collection	Patch
@tanstack/query-db-collection	Patch
@tanstack/react-db	Patch
@tanstack/rxdb-db-collection	Patch
@tanstack/solid-db	Patch
@tanstack/svelte-db	Patch
@tanstack/trailbase-db-collection	Patch
@tanstack/vue-db	Patch

Not sure what this means? Click here to learn what changesets are.

Click here if you're a maintainer who wants to add another changeset to this PR

[samwillis]

Hey @melvinhagberg

Just to check the intention of this fix. Am I correct that what you were experiencing was that the page would briefly show valid data for the query, but data that would not be the first page, and appear incorrect? So for example, after changing the orderBy, it would show the data that had already loaded (as its in the on-demand collection) until the "true" first page had loaded from the server?

I'm a little hesitant of the coarseness of this change (it's scoped to the source collection, and flicks on after the first loadSubset), and that it defaults to enabled.

I think we have a few options:

1. Something like this, but make it scoped to the useLiveInfiniteQuery call site. Essentially ensuring that it always waits for the promise from the first loadSubset to return before we loading state changes. We essentially then always go to the server.
2. Do 1, but make it opt in.
3. Make a much more intelligent tracking of the queries and determine if the first page is already covered by what we have loaded in the collection. I think we have some of the part need for this with the "loadSnapshot Deduper", but it's a more complex solve.