fix(db): isolate reused subquery placements

[KyleAMathews]

Reusing one subquery builder in both FROM and JOIN now behaves like two lexical placements of the same relation. Same-key self-joins no longer collapse to an empty result.

Root cause

CollectionRef.sourceId identifies a lexical source position, but embedding a query builder reused its existing IR and therefore reused its source IDs. The live-query graph then treated both sides of a self-join as one source position. Changing or bypassing the compiled-query cache did not help because the collision existed before compilation.

Approach

• Clone a subquery's IR when it is placed into another query.
• Preserve the query's expressions, callbacks, Collections, and public semantics while assigning fresh IDs to nested CollectionRef nodes.
• Clone nested query/include structure safely, retaining shared and cyclic object topology with a WeakMap.
• Apply the placement boundary to FROM, JOIN, and included subqueries.

Key invariants

• A source ID belongs to one lexical query-source placement, not to a Collection or reusable builder.
• Reused placements still read the same underlying Collections.
• Optimizer and compiled-query cache semantics remain unchanged.
• Auto-index off and eager produce the same public rows.

Non-goals

• This does not redesign the compiled-query cache.
• This does not allow duplicate aliases across unionAll branches; that existing validation remains unchanged.
• This does not change query types or public APIs.

Trade-offs

Cloning the small IR tree at placement time does modest extra construction work, but keeps runtime graph ownership explicit. Caching a logical plan factory could also instantiate fresh graph state, but would be a substantially larger compiler redesign.

Verification

pnpm vitest run --pool-options.threads.maxThreads=2 packages/db/tests/query/join-subquery.test.ts packages/db/tests/query/compiler/subquery-caching.test.ts packages/db/tests/query/optimizer.test.ts packages/db/tests/query/ir-stable-identity.test.ts packages/db/tests/query/union-all.test.ts packages/db/tests/query/builder/union-all.test.ts
pnpm exec eslint packages/db/src/query/builder/clone-query.ts packages/db/src/query/builder/index.ts packages/db/tests/query/join-subquery.test.ts
pnpm exec tsc --noEmit -p packages/db/tsconfig.json
pnpm --filter @tanstack/db build

The focused test set passes 200/200.

Files changed

• clone-query.ts: cycle-safe placement cloning with fresh source identities.
• builder/index.ts: clones builders at subquery and include placement boundaries.
• join-subquery.test.ts: shared-versus-separate builder matrix across predicate and auto-index modes.
• Changeset: records the runtime bug fix for @tanstack/db.

---

Stacked on #1877, which supplies the adjacent pushed-predicate and alias-remapping fixes.

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commit: 6560ad0

[github-actions]

Size Change: +774 B (+0.47%)

Total Size: 167 kB

📦 View Changed

Filename	Size	Change
packages/db/dist/esm/query/builder/clone-query.js	743 B	+743 B (new file)	🆕
packages/db/dist/esm/query/builder/index.js	6.72 kB	+31 B (+0.46%)

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Filename	Size
packages/db/dist/esm/client.js	3.66 kB
packages/db/dist/esm/collection-options.js	236 B
packages/db/dist/esm/collection/change-events.js	1.44 kB
packages/db/dist/esm/collection/changes.js	2.4 kB
packages/db/dist/esm/collection/cleanup-queue.js	794 B
packages/db/dist/esm/collection/events.js	481 B
packages/db/dist/esm/collection/index.js	4.36 kB
packages/db/dist/esm/collection/indexes.js	1.99 kB
packages/db/dist/esm/collection/lifecycle.js	2.15 kB
packages/db/dist/esm/collection/mutations.js	2.61 kB
packages/db/dist/esm/collection/state.js	6.51 kB
packages/db/dist/esm/collection/subscription.js	8.73 kB
packages/db/dist/esm/collection/sync.js	4.63 kB
packages/db/dist/esm/collection/transaction-metadata.js	144 B
packages/db/dist/esm/deferred.js	207 B
packages/db/dist/esm/errors.js	5.26 kB
packages/db/dist/esm/event-emitter.js	964 B
packages/db/dist/esm/index.js	3.71 kB
packages/db/dist/esm/indexes/auto-index.js	829 B
packages/db/dist/esm/indexes/base-index.js	1.14 kB
packages/db/dist/esm/indexes/basic-index.js	2.07 kB
packages/db/dist/esm/indexes/btree-index.js	2.26 kB
packages/db/dist/esm/indexes/index-registry.js	820 B
packages/db/dist/esm/indexes/reverse-index.js	376 B
packages/db/dist/esm/live-query-adapter.js	318 B
packages/db/dist/esm/live-query-observer.js	3.69 kB
packages/db/dist/esm/live-query-options.js	702 B
packages/db/dist/esm/live-query-window-controller.js	4.36 kB
packages/db/dist/esm/local-only.js	989 B
packages/db/dist/esm/local-storage.js	2.17 kB
packages/db/dist/esm/optimistic-action.js	359 B
packages/db/dist/esm/paced-mutations.js	496 B
packages/db/dist/esm/proxy.js	3.32 kB
packages/db/dist/esm/query/builder/functions.js	1.47 kB
packages/db/dist/esm/query/builder/query-ir.js	116 B
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packages/db/dist/esm/query/compiler/evaluators.js	1.96 kB
packages/db/dist/esm/query/compiler/expressions.js	560 B
packages/db/dist/esm/query/compiler/group-by.js	4.13 kB
packages/db/dist/esm/query/compiler/index.js	9.11 kB
packages/db/dist/esm/query/compiler/joins.js	2.99 kB
packages/db/dist/esm/query/compiler/lazy-targets.js	1.1 kB
packages/db/dist/esm/query/compiler/order-by.js	1.91 kB
packages/db/dist/esm/query/compiler/parent-routes.js	319 B
packages/db/dist/esm/query/compiler/query-equivalence.js	455 B
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packages/db/dist/esm/query/compiler/select.js	1.58 kB
packages/db/dist/esm/query/effect.js	4.6 kB
packages/db/dist/esm/query/equality-value-identity.js	591 B
packages/db/dist/esm/query/expression-helpers.js	1.43 kB
packages/db/dist/esm/query/ir-stable-identity.js	4.04 kB
packages/db/dist/esm/query/ir.js	1.59 kB
packages/db/dist/esm/query/live-query-collection.js	391 B
packages/db/dist/esm/query/live/bucket-facade-adapter.js	2.73 kB
packages/db/dist/esm/query/live/collection-config-builder.js	6.97 kB
packages/db/dist/esm/query/live/collection-registry.js	264 B
packages/db/dist/esm/query/live/collection-subscriber.js	2.26 kB
packages/db/dist/esm/query/live/internal.js	145 B
packages/db/dist/esm/query/live/materialized-pipeline.js	2.32 kB
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packages/db/dist/esm/query/optimizer.js	3.05 kB
packages/db/dist/esm/query/query-once.js	359 B
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packages/db/dist/esm/strategies/debounceStrategy.js	247 B
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packages/db/dist/esm/strategies/throttleStrategy.js	246 B
packages/db/dist/esm/transactions.js	3.71 kB
packages/db/dist/esm/utils.js	1.08 kB
packages/db/dist/esm/utils/array-utils.js	270 B
packages/db/dist/esm/utils/browser-polyfills.js	304 B
packages/db/dist/esm/utils/btree.js	4.51 kB
packages/db/dist/esm/utils/callbacks.js	174 B
packages/db/dist/esm/utils/comparison.js	1.49 kB
packages/db/dist/esm/utils/cursor.js	676 B
packages/db/dist/esm/utils/error.js	167 B
packages/db/dist/esm/utils/get-or-create.js	155 B
packages/db/dist/esm/utils/index-optimization.js	2.42 kB
packages/db/dist/esm/utils/type-guards.js	230 B
packages/db/dist/esm/utils/uuid.js	449 B
packages/db/dist/esm/virtual-props.js	360 B

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Size Change: 0 B

Total Size: 7.34 kB

ℹ️ View Unchanged

Filename	Size
packages/react-db/dist/esm/DbProvider.js	317 B
packages/react-db/dist/esm/HydrationBoundary.js	263 B
packages/react-db/dist/esm/index.js	330 B
packages/react-db/dist/esm/live-query-internals.js	282 B
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packages/react-db/dist/esm/usePacedMutations.js	401 B

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