fix(signals): draft reads compose overrides over a truth-staged backing

[brenelz]

Summary

With several optimistic-store actions in flight (optimistic votes++, server confirm, refresh(store)), rapid clicks rendered 1, 2, 3, 4, then fell back to 2, then 5, while the server counted every vote. Reproduces identically at the core with a plain promise source and with an async-generator (live stream) source, so the transport is not involved.

Root cause

When the first vote's truth lands while the second is still retained, the landing is staged into the retaining transaction (#3164 fold) and the second vote's +1 replays over it. A third click's draft then read the staged truth without the replayed override: the four draft-read paths (data key, hot path, has, ownKeys) composed live overrides only while target.pb === null, on the assumption that an existing pending backing was the draft's own view-seeded clone. A truth-staged backing is authoritative truth without overrides. ensurePB's hand-off parks such a backing and reseeds from the view on the draft's first write, but votes++ reads first — it read base, wrote base + 1, and the override it emitted landed on the value already displayed. The click was invisible and the count stuck (or fell back) until truth caught up.

Minimal sequence:

step	expected	before
click A	1	1
click B	2	2
A's truth (1) lands, B retained	2	2
click C	3	2
B's truth (2) lands	3	2
C's truth (3) lands	3	3

Fix

draftSeesOverrides(target): draft reads compose overrides whenever the pending backing is not the draft's own tentative clone (tentativePBs), applied to all four draft paths. Nothing changes for a draft that has opened its own backing (reads must see its writes) or for authoritative drafts.

Tests

tests/optimistic-store-refetch-hold.test.ts gains "#2951 compose half": three votes in flight, the third made after the first landing, every visible value monotonic. Fails without the fix at click C (expected 2 to be 3). A ten-click replay on the app's exact schedule renders 1 through 10 with each click instant. Full signals suite, solid suite, and the web Loading/optimistic/store specs pass on the rebuilt dist.

🤖 Generated with Claude Code

[changeset-bot]

🦋 Changeset detected

Latest commit: 0212cba

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-hq]

Merging this PR will not alter performance

✅ 136 untouched benchmarks

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_{Comparing brenelz:fix/optimistic-draft-reads-compose (0212cba) with next (439a2fe)}