fix(electric-db-colleciton): ignore snapshot-end before up-to-date

[samwillis]

🎯 Changes

CI run failing with the reproduction from before fixing: https://github.com/TanStack/db/actions/runs/19739188291/job/56558506582?pr=924

Issue

In eager sync mode, a snapshot-end message arriving before the first up-to-date message was incorrectly triggering a commit, making data visible prematurely.

Root Cause

Electric adds a snapshot-end marker after the initial snapshot data in the log. However, this snapshot-end can be from a significant period before the stream is actually up to date (i.e., fully synced with the current state of the database). The existing code at line 993 in electric.ts:

if (hasUpToDate || hasSnapshotEnd) {

...would enter the commit logic for either message type. In the else branch, transactions were committed whenever snapshot-end arrived, even before the first up-to-date:

} else {
  // Normal mode or on-demand: commit transaction if one was started
  if (transactionStarted) {
    commit()
    transactionStarted = false
  }
}

This caused eager mode to show potentially stale/incomplete data to users before the stream was truly up to date.

Note: progressive mode was already protected because it buffers messages during isBufferingInitialSync() and only commits on up-to-date. on-demand mode is not affected because the log is in changes_only mode and doesn't have an initial snapshot.

Fix

Modified the commit logic to only commit on snapshot-end if:

1. It's an up-to-date message, OR
2. It's on-demand mode (where snapshot-end semantically means "ready"), OR
3. The first up-to-date has already been received (hasReceivedUpToDate is true)

const shouldCommit =
  hasUpToDate ||
  syncMode === `on-demand` ||
  hasReceivedUpToDate

if (transactionStarted && shouldCommit) {
  commit()
  transactionStarted = false
}

This ensures that in eager mode, snapshot-end before the first up-to-date is ignored (no commit), while subsequent snapshot-end messages (after the first up-to-date) will correctly trigger commits.

Tests

• Added test: should ignore snapshot-end before first up-to-date in progressive mode
• Added test: should commit on snapshot-end in eager mode AFTER first up-to-date
• Updated test: should NOT commit multiple snapshot-end messages before up-to-date in eager mode

✅ 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: 1e178db

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

This PR includes changesets to release 2 packages

Name	Type
@tanstack/electric-db-collection	Patch
@tanstack/db-collection-e2e	Patch

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commit: 1e178db

[github-actions]

Size Change: 0 B

Total Size: 87 kB

ℹ️ View Unchanged

Filename	Size
./packages/db/dist/esm/collection/change-events.js	1.38 kB
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./packages/db/dist/esm/collection/events.js	388 B
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./packages/db/dist/esm/collection/lifecycle.js	1.67 kB
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./packages/db/dist/esm/collection/state.js	3.43 kB
./packages/db/dist/esm/collection/subscription.js	2.55 kB
./packages/db/dist/esm/collection/sync.js	2.37 kB
./packages/db/dist/esm/deferred.js	207 B
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./packages/db/dist/esm/indexes/auto-index.js	742 B
./packages/db/dist/esm/indexes/base-index.js	766 B
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./packages/db/dist/esm/indexes/reverse-index.js	513 B
./packages/db/dist/esm/local-only.js	837 B
./packages/db/dist/esm/local-storage.js	2.1 kB
./packages/db/dist/esm/optimistic-action.js	359 B
./packages/db/dist/esm/paced-mutations.js	496 B
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./packages/db/dist/esm/query/builder/functions.js	733 B
./packages/db/dist/esm/query/builder/index.js	3.96 kB
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./packages/db/dist/esm/query/compiler/expressions.js	430 B
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./packages/db/dist/esm/query/ir.js	673 B
./packages/db/dist/esm/query/live-query-collection.js	360 B
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./packages/db/dist/esm/query/optimizer.js	2.56 kB
./packages/db/dist/esm/query/predicate-utils.js	2.91 kB
./packages/db/dist/esm/query/subset-dedupe.js	921 B
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./packages/db/dist/esm/strategies/debounceStrategy.js	247 B
./packages/db/dist/esm/strategies/queueStrategy.js	428 B
./packages/db/dist/esm/strategies/throttleStrategy.js	246 B
./packages/db/dist/esm/transactions.js	2.9 kB
./packages/db/dist/esm/utils.js	881 B
./packages/db/dist/esm/utils/browser-polyfills.js	304 B
./packages/db/dist/esm/utils/btree.js	5.61 kB
./packages/db/dist/esm/utils/comparison.js	852 B
./packages/db/dist/esm/utils/index-optimization.js	1.51 kB
./packages/db/dist/esm/utils/type-guards.js	157 B

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[github-actions]

Size Change: 0 B

Total Size: 3.34 kB

ℹ️ View Unchanged

Filename	Size
./packages/react-db/dist/esm/index.js	225 B
./packages/react-db/dist/esm/useLiveInfiniteQuery.js	1.17 kB
./packages/react-db/dist/esm/useLiveQuery.js	1.11 kB
./packages/react-db/dist/esm/useLiveSuspenseQuery.js	431 B
./packages/react-db/dist/esm/usePacedMutations.js	401 B

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[kevin-dp]

Good catch!

[github-actions]

🎉 This PR has been released!

• @tanstack/electric-db-collection@0.2.9

Thank you for your contribution!