fix(svelte-query): untrack observer subscription

[gzuuus]

Fixes #11541

🎯 Changes

For queries without cached data, queryFn executes synchronously inside the subscription $effect (onSubscribe → shouldFetchOnMount → fetch). Any reactive state read by queryFn before its first await was therefore recorded as a dependency of that effect. Writes to that state tore the observer down (cancelling the in-flight fetch) and re-subscribed — and since the query stays dataless, every re-subscription starts a new fetch: an unbounded teardown/refetch loop. See #11541 for the full mechanism and the exact set of conditions that sustain it.

The fix keeps the observer read tracked, but runs the subscription itself inside untrack():

$effect(() => {
  const o = observer
  const unsubscribe = isRestoring.current
    ? () => undefined
    : untrack(() => o.subscribe(() => update(createResult())))
  return unsubscribe
})

Note: the naive untrack(() => observer.subscribe(...)) is not enough — it also untracks the observer read, so changing queries would no longer re-subscribe. The existing test “should track queries added to an initially empty array” catches that case, which is why the observer read stays outside the untrack().

Applied to both createBaseQuery.svelte.ts (also covers createInfiniteQuery) and createQueries.svelte.ts.

✅ Checklist

• I have followed the steps in the Contributing guide.
• I have tested code changes locally with pnpm run test:pr, or these tests do not apply to this pull request.
• I fully understand the code in this pull request, including any code generated with AI assistance.

🚀 Release Impact

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

Summary by CodeRabbit

• Bug Fixes

  • Prevented reactive state updates during an in-flight query from unnecessarily restarting subscriptions or cancelling fetches.
  • Query functions that read state before their first asynchronous wait now complete reliably without repeated refetches.

• Tests

  • Added regression coverage for single-fetch behavior and successful completion in both individual and multiple-query scenarios.

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ℹ️ Recent review info

⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between d346e85 and 23136f4.

📒 Files selected for processing (5)

• .changeset/svelte-query-untrack-subscribe.md
• packages/svelte-query/src/createBaseQuery.svelte.ts
• packages/svelte-query/src/createQueries.svelte.ts
• packages/svelte-query/tests/createQueries/createQueries.svelte.test.ts
• packages/svelte-query/tests/createQuery/createQuery.svelte.test.ts

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📝 Walkthrough

Walkthrough

The Svelte Query subscription effects now execute observer subscriptions inside untrack(). Observer reads remain tracked. Regression tests cover reactive state access during asynchronous query functions, and a patch changeset records the fix.

Changes

Svelte Query subscription fix

Layer / File(s)	Summary
Untrack observer subscriptions packages/svelte-query/src/createBaseQuery.svelte.ts, packages/svelte-query/src/createQueries.svelte.ts	Both subscription effects capture the observer before calling subscribe inside untrack().
Regression coverage and release metadata packages/svelte-query/tests/createQuery/createQuery.svelte.test.ts, packages/svelte-query/tests/createQueries/createQueries.svelte.test.ts, .changeset/svelte-query-untrack-subscribe.md	Tests verify one fetch and successful completion when query functions read and update reactive state during asynchronous execution. The changeset records a patch release for @tanstack/svelte-query.

Priority: ➖ Normal

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Bug fix · Severity of issue fixed: Medium

Suggested reviewers: sukvvon

Merge Risk: ⚪ Minimal · up to 23136

The subscription change preserves query reactivity and cleanup while preventing reactive query-function reads from causing refetch loops. No actionable merge-blocking risk remains.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely describes the main change: running the Svelte Query observer subscription inside untrack().
Description check	✅ Passed	The description includes all required template sections, explains the motivation and implementation, confirms testing and contributor checks, and documents the changeset release impact.
Linked Issues check	✅ Passed	The change meets the coding requirements in [#11541]. createBaseQuery.svelte.ts reads observer into o before it runs o.subscribe(...) inside untrack(). The observer read remains tracked, so …
Out of Scope Changes check	✅ Passed	The changeset, source changes, explanatory comments, and regression tests directly support [#11541]. The pull request changes only observer subscription tracking for the affected Svelte Query paths. N…
Docstring Coverage	✅ Passed	Docstring coverage is 100.00% which is sufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 2 functions across 4 files. (1 skipped: 1 …

✨ Finishing Touches

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