fix(signals): a Show branch mounted by a held write reads the value that mounted it (#4010)

[ryansolid]

Requested by Ryan · project thread

Fixes #4010.

Before: when a held write mounts a <Show> branch, a binding inside it that re-runs before the transaction lands (an isPending reader, or a plain binding re-run by a live write) is served the committed screen, where the Show condition is still null. item().name throws into <Errored>, and since #3977 the unchanged landing never re-runs it, so the error sticks.

After: the branch's bindings read the transaction that mounted them until it lands. No error, and the final screen is correct.

How: holdFrame already visits exactly the held frame's members, so it now tags each with an internal CONFIG_HELD_FRAME bit (cleared in commitPendingNode with CONFIG_HELD, and defensively at the three lane sites that drop CONFIG_HELD). A new internal bornInto(c, t) treats a tagged member like a never-run node, born into t. It is used in frameRead, stagedScreen and recompute. observeFlight (in verdict.ts, so only isPending/latest users pay) makes such a member wait on its own transaction's flight; without that gate a keyed branch that probes and reads the flight loops forever. Each of the four sites is needed: removing any one fails at least one new test.

Size

+89 B minified in the always-loaded signals core (+121 B with isPending/latest). Ten scenarios crossed their caps; each is raised to measured + 10 B rounded up to 0.01 KB, with a dated ledger note in scripts/size/scenarios.js. Two of them are frozen floor caps in floor-caps.json: core floor 7.45 -> 7.48 KB and the simple-app floor 9.94 -> 9.98 KB. Hello world stays under 10 KB at 9,966 B.

Size-Exception: accepted by the maintainer (2026-10-13) — #4010's held-frame tag lives in the always-loaded core read path; hello world stays under 10 KB.

Behavior note

A never-run verdict reader that reads its own transaction's held flight now waits on it instead of seeing the committed value. Consistent with A29 ("a node born into the future has no screen"); no existing test pinned the old behavior.

Public API changes

None. bornInto and CONFIG_HELD_FRAME are internal.

How did you test this change?

• packages/signals/tests/held-branch-verdict-reader-4010.test.ts (4 tests) and packages/web/test/show-held-branch-verdict-reader-4010.spec.tsx (the reporter's repro, count 0 and 1). All fail on unmodified next.
• signals 5201 passed; solid-js 856/856; web jsdom 1391/1391; web hydrate unchanged; web server has 1 failure that also fails on next (server-functions-adapter-request.spec.tsx). Typecheck clean.
• scripts/size: every scenario within its cap; check-floor-caps passes with the Size-Exception line.

🤖 Generated with Claude Code

https://claude.ai/code/session_01NcUAu8BQ6Xsf8XRBhr9V1w

[changeset-bot]

🦋 Changeset detected

Latest commit: 73c288c

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

This PR includes changesets to release 13 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
board-example	Patch
todos-server-example	Patch

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[github-actions]

Size (brotli, eager entry chunk)

scenario	head	vs base	minified vs base	minified vs recorded	cap		lazy chunks (not counted)
signals: core floor (createSignal/Memo/Effect/Root/flush)	7.47 KB	+25 B (+0.3%)	+89 B	0 B	7.48 KB	✅
signals: + createStore	14.93 KB	+48 B (+0.3%)	+89 B	0 B	14.94 KB	✅
signals: + isPending/latest	9.75 KB	+47 B (+0.5%)	+121 B	0 B	9.77 KB	✅
app: render + one signal (the simple-app floor)	9.97 KB	+47 B (+0.5%)	+89 B	0 B	9.98 KB	✅
app: hydrating (no stores) with Show/For/Loading/Errored/lazy	17.89 KB	+51 B (+0.3%)	+89 B	−77 B	17.93 KB	✅	lazy-page.js 0.04 KB
app: hydrating + every store primitive family	29.44 KB	−15 B (−0.1%)	+100 B	+128 B	29.50 KB	✅	lazy-page.js 0.04 KB
app: CSR with Show/For/Loading/Errored/lazy	13.05 KB	+46 B (+0.4%)	+89 B	0 B	13.07 KB	✅	lazy-page.js 0.04 KB
app: CSR, observe tier (same app on the observe artifacts)	14.62 KB	+2 B (+0.0%)	+89 B	0 B	14.64 KB	✅	lazy-page.js 0.04 KB
app: CSR, observe tier + attribution engine enabled	28.98 KB	+54 B (+0.2%)	+89 B	0 B	29.00 KB	✅	lazy-page.js 0.04 KB
app: compiled floor (one template, one text hole, one delegated click)	10.15 KB	+16 B (+0.2%)	+89 B	0 B	10.17 KB	✅
app: compiled CSR (JSX todo app: spread/merge/omit, events, class/style, keyed For, Show, Loading + lazy, store)	25.74 KB	+93 B (+0.4%)	+89 B	0 B	25.75 KB	✅	stats.js 0.18 KB
app: compiled hydrating (the same JSX todo app through hydrate(), compiled hydratable)	31.61 KB	+49 B (+0.2%)	+89 B	0 B	31.62 KB	✅	stats.js 0.20 KB
frames: eager client consumer (frames client + transport, lazy codec)	11.43 KB	0 B	0 B	0 B	11.43 KB	✅
page: base server components (hydrating + dynamic + frames + sf reference)	34.17 KB	+90 B (+0.3%)	+89 B	−1626 B	34.33 KB	✅	assets.js 0.78 KB, bind.js 1.83 KB, decode.js 6.23 KB, lazy-page.js 0.04 KB, regions.js 0.80 KB, trace.js 8.99 KB, wire.js 0.93 KB
page: live server components (base + live/GET + action + isPending/latest)	37.87 KB	+13 B (+0.0%)	+121 B	−1682 B	38.15 KB	✅	assets.js 0.78 KB, bind.js 1.83 KB, decode.js 6.23 KB, lazy-page.js 0.04 KB, regions.js 0.80 KB, trace.js 8.99 KB, wire.js 0.93 KB
page: compiled base server components (the base page as JSX: templates with class/style/attributes/events, For/Show; no spread)	34.95 KB	−18 B (−0.1%)	+89 B	−2704 B	35.66 KB	✅	assets.js 0.78 KB, bind.js 1.83 KB, decode.js 6.23 KB, regions.js 0.80 KB, sc-comments.js 0.20 KB, trace.js 8.95 KB, wire.js 0.93 KB
page: compiled live server components (the compiled base page + live/GET + action + isPending/latest)	40.55 KB	+46 B (+0.1%)	+138 B	−2697 B	41.21 KB	✅	eager (counted): web.js 21.50 KB; assets.js 0.78 KB, bind.js 1.84 KB, decode.js 6.23 KB, regions.js 0.79 KB, sc-comments.js 0.19 KB, trace.js 8.93 KB, wire.js 0.93 KB
page: base + router (base page + @solidjs/router: createRouter, two routes, preload, useNavigate)	41.49 KB	+117 B (+0.3%)	+83 B	−1619 B	41.79 KB	✅	assets.js 0.78 KB, bind.js 1.85 KB, decode.js 6.23 KB, lazy-page.js 0.04 KB, regions.js 0.80 KB, server.js 1.02 KB, serverForms.js 3.58 KB, trace.js 8.98 KB, wire.js 0.94 KB
page: live + router (live page + @solidjs/router: createRouter, two routes, preload, useNavigate)	47.21 KB	+24 B (+0.1%)	+139 B	−1612 B	47.49 KB	✅	eager (counted): client.js 27.69 KB; assets.js 0.78 KB, bind.js 1.84 KB, decode.js 6.23 KB, lazy-page.js 0.04 KB, regions.js 0.81 KB, server.js 1.02 KB, serverForms.js 3.30 KB, trace.js 8.96 KB, wire.js 0.94 KB
server: floor (getRequestEvent + isServer)	1.33 KB	0 B	0 B	0 B	1.34 KB	✅
server: renderToString (the server-render floor)	20.47 KB	0 B	0 B	0 B	20.48 KB	✅

_{Bundled with Rolldown (what Vite ships), brotli q11, decimal KB. A scenario fails only when it is over its brotli cap and its minified size is more than 20 B over the minified recorded with the cap; over the cap within that allowance is brotli layout noise and passes with a warning. Caps and their recorded minified in scripts/size/scenarios.js; the floor and page caps in floor-caps.json are frozen (lower only, or Size-Exception: in the PR body). npm run ratchet lowers caps per RC; it never raises one (scripts/size/README.md).}

[ryansolid]

The Size check is red because of this PR: the fix adds +89 B minified to always-loaded floor code, which puts 10 scenarios over their caps (core floor by 18 B, compiled CSR by 86 B, the rest by 17 to 37 B). It's not a flake, so I haven't re-run it. The floor caps are frozen, so this waits on a maintainer decision: either raise the caps with a Size-Exception note, or find an offset elsewhere in the floor. The tests are green.

— Claude via Claude Code

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Generated by Claude Code

[coveralls]

Coverage Report for CI Build 38436719295

Coverage remained the same at 77.429%

Details

• Coverage remained the same as the base build.
• Patch coverage: No coverable lines changed in this PR.
• No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

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Coverage Stats

Relevant Lines:	1321
Covered Lines:	1079
Line Coverage:	81.68%
Relevant Branches:	1036
Covered Branches:	746
Branch Coverage:	72.01%
Branches in Coverage %:	Yes
Coverage Strength:	27.13 hits per line

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💛 - Coveralls

[codspeed]

Merging this PR will improve performance by 9.56%

⚠️ 2 benchmarks spent significant time in system calls

System calls cannot be consistently instrumented, so they are not included in the measure, which understates the real cost. Please switch to the Walltime instrument to accurately measure system calls.

Measurement and system calls

• readAllowed
• propagation:diamond

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 2 improved benchmarks
✅ 193 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	createStore setter: delete + set one root key (#3044 overlay)	2.1 ms	1.8 ms	+13.5%
⚡	memo + sync render effect only (reference)	28.2 ms	26.6 ms	+5.75%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing claude/project-thread-w8qjvi-4010 (73c288c) with next (25935fe)}

[ryansolid]

Two red checks, neither from the fix's code:

• Size check: every scenario is now within its raised cap. Only the check-floor-caps step fails, because it reads SIZE_EXCEPTION from the pull_request event payload, which still holds the PR body from before the Size-Exception: line was added. Editing the body doesn't fire a new event and a re-run reuses the old payload, so it passes on the next push to this branch.
• CodSpeed: dbmon shallow full tick reads −7%. CodSpeed flags that it compared across different runtime environments, the same code (b26f40e) showed no change on its earlier run, and that store benchmark never enters a held frame. I've re-run the benchmarks once.

— Claude via Claude Code

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Generated by Claude Code