fix(signals): keep a mainline effect value out of its parked transaction (#3412)

[brenelz]

Fixes #3412

Problem

With a Loading on={count()} boundary and an unconditional details() reader outside it, flipping show to false while details is still pending leaves show() ? details() : "hidden" displaying the old value until the unrelated async settles.

Cause

The count write opens a transaction that stays parked (Details and Panel read details() outside any boundary), and both effects are stamped with it. On the later ambient show write, Panel recomputes mainline, reads show as false, and publishes "hidden" into _value with mainline ownership — which is what the flush's "everything computed mainline applies now" rule expects.

recompute then forces a second run of the effect inside its own parked transaction to refresh the staged view. That re-run only writes _pendingValue, but it also re-stamped _valueTransition to the parked transaction, claiming ownership of the value the mainline run produced.

During finalization the boundary sweep sees copy settled and writes _disabled = false. That signal is stamped with the parked transaction (its on reset staged the fallback flip there), so the write legitimately re-enters it mid-flush. With the transaction active and Panel's ownership pointing at it, the runEffect ownership gate leaves Panel queued and the next pass parks it. Show applies because it was never stamped.

Without on, nothing re-enters the transaction in that flush, so the misattributed ownership is harmless and Panel applies by accident — which is why the minimization looks like a boundary bug.

Fix

Save _valueTransition before the forced in-transaction re-run and restore it afterward. The contested-effect bookkeeping is untouched, so the transaction still re-derives the effect against its own committed world at commit.

Tests

• packages/signals/tests/effect-mainline-ownership-3412.test.ts — the four-variant matrix (boundary / on / unconditional reader) at the signals level; only the reporter's shape failed before the fix.
• packages/web/test/loading-on-outside-reader-3412.spec.tsx — the same matrix rendered through @solidjs/web.
• Full signals suite (1775 passed) and web suite (740 passed) are green with the fix.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: b28a7ea

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

This PR includes changesets to release 11 packages

Name	Type
@solidjs/signals	Patch
test-integration	Patch
@solidjs/web	Patch
@solidjs/babel-plugin	Patch
@solidjs/compiler	Patch
@solidjs/diagnostics	Patch
@solidjs/element	Patch
@solidjs/h	Patch
@solidjs/html	Patch
solid-js	Patch
@solidjs/universal	Patch

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[codspeed]

Merging this PR will not alter performance

✅ 160 untouched benchmarks

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_{Comparing brenelz:investigate/loading-reset-stale-3412 (b28a7ea) with next (7f6332a)}