fix(signals): affects() as an action's first statement never lights isPending

[brenelz]

Summary

Fixes #2887 — affects(store) declared as the first statement of an action (before any optimistic write) never read as pending through tracked isPending probes for the duration of the action; the badge blipped true for a single tick at settle instead. Moving the same affects call after the first write worked, exactly as the issue describes.

Root cause

affects() on a lane-less node writes true into the node's isPending companion signal, which (being the first optimistic write) creates a lane for the companion. Companion lanes must stay children of their owner's lane so their effects flush immediately instead of waiting on the transaction's async — but the parent link was captured only at lane creation from parentSource._optimisticLane. With affects first, the owner has no lane yet, so the companion lane was born parentless. The action's optimistic write then reached the shared subscriber (the badge memo), found no parent-child relation in assignOrMergeLane, and merged the companion's lane into the store's async-carrying lane. runLaneEffects skips lanes with pending async, so every tracked reader of the verdict deferred to settle.

The mark itself was held correctly the whole time (refcount, untracked probes read true) — only tracked/effect-driven readers were starved.

Fix

When an owner's lane is created in getOrCreateLane, adopt any lane its companions (_pendingSignal, _latestValueComputed) already created as a child of the new lane — the parent-child relation becomes a property of the nodes rather than of write order. Adoption is guarded to the companion's own unmerged, still-parentless root, so a lane group that has absorbed unrelated work is never re-parented.

Testing

• New regression test in affects-propagation.test.ts reproducing the issue's setup (derived optimistic store + live mapArray subscriber + tracked badge memo): fails without the fix (badge log stays empty during the action), passes with it.
• Full suites pass: solid-signals, solid, solid-web; package typecheck clean.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 06d821d

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

This PR includes changesets to release 9 packages

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

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[codspeed-hq]

Merging this PR will not alter performance

✅ 7 untouched benchmarks
⏩ 113 skipped benchmarks¹

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_{Comparing brenelz:fix/affects-first-statement-lane (06d821d) with next (587cf48)}

Footnotes

1. 113 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩