test(web,signals): tier-1 coverage for the headless-UI props chain

[ryansolid]

What

Tier-1 benches and tests for the shape every headless-UI library (Kobalte) renders per element: merge(defaults) → omit(consumed) → compiler mergeProps(call-site statics) stacked per component layer, ending in a polymorphic dynamic(() => props.as) and one spread.

The existing utilities.bench.ts / spread-enumerate.bench.tsx / dynamic-tag.bench.tsx each measure one op in isolation, and each looks cheap. The chain is where the cost lives — every layer re-processes every key of the layer below — and nothing in the repo measured or pinned it, so it was invisible to CodSpeed.

Fixture

One shared source, packages/web/test/harness/polymorphic.tsx: Dialog.Trigger → Button.Root → Polymorphic mirroring the kobalte solid2 branch (context-driven aria, defaults, consumed keys, as="a" override shadowing the default), plus a CompiledRow floor twin that writes the same <a> directly. The DOM bench, SSR bench, parity scenario, and specs all render this identical tree, compiled by each project's generate.

Added

	file	measures / pins
bench	web/test/polymorphic-chain.bench.tsx	DOM: mount+clear 1k, update 10th ×16; owner-drift gated; chain vs floor
bench	web/test/server/polymorphic-chain.bench.tsx	SSR: renderToString 200 rows; chain vs floor (pure construction cost)
bench	signals/tests/store/props-chain.bench.ts	merge/omit chain at depth 1/3/7; build and build + consume separately
harness	polymorphic-chain, polymorphic-chain-compiled-floor scenarios	hydration ids through the chain, element identity across update, adopt-all, no separators
spec	web/test/polymorphic-chain.spec.tsx, server/polymorphic-chain.spec.tsx	chain resolves to the floor's exact attribute set; consumed keys and as absent; reactive attrs live; element kept across updates; SSR same set + keys
spec	signals/tests/store/utilities.test.ts "props chain"	shadowing order, hidden keys accumulate through nested omits and survive re-merges, live reads through every layer, spread-copy snapshot, descriptor kind (data vs getter) survives to the bottom of the chain

The last one is the contract the upcoming view work must keep: a consumer at the bottom of the chain (spread's children fast path, static-source detection) has to be able to read the compiler's static/dynamic verdict for a key.

Baseline (next, this machine)

lane	compiled floor	chain	ratio
SSR, 200 rows	0.21 ms	3.87 ms	18× (≈19 µs/element)
DOM mount+clear 1k	20 ms	49 ms	2.5×
DOM update 100/1k ×16	2.8 ms	6.3 ms	2.3×
signals chain depth 3	—	21 µs
signals chain depth 7	—	65 µs

No source changes, no changeset. Both compilers verified (JSX_COMPILER=babel A/B on the specs and harness).

[changeset-bot]

⚠️ No Changeset found

Latest commit: 9f465d5

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[coveralls]

Coverage Report for CI Build 34934352482

Warning

No base build found for commit a5d8eae on next.
Coverage changes can't be calculated without a base build.
If a base build is processing, this comment will update automatically when it completes.

Coverage: 71.842%

Details

• Patch coverage: No coverable lines changed in this PR.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

Requires a base build to compare against. How to fix this →

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Coverage Stats

Relevant Lines:	1007
Covered Lines:	772
Line Coverage:	76.66%
Relevant Branches:	790
Covered Branches:	519
Branch Coverage:	65.7%
Branches in Coverage %:	Yes
Coverage Strength:	15.1 hits per line

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💛 - Coveralls

[codspeed]

Merging this PR will improve performance by 12.09%

⚠️ 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

⚡ 1 improved benchmark
✅ 159 untouched benchmarks
🆕 12 new benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	projection derive: write one NESTED field (reference)	2.8 ms	2.5 ms	+12.09%
🆕	build	N/A	286.3 µs	N/A
🆕	build + consume	N/A	271.1 µs	N/A
🆕	build	N/A	509.1 µs	N/A
🆕	build + consume	N/A	486.4 µs	N/A
🆕	build	N/A	2.4 ms	N/A
🆕	build + consume	N/A	1.1 ms	N/A
🆕	polymorphic-chain mount+clear 1000 rows: chain	N/A	841.9 ms	N/A
🆕	polymorphic-chain mount+clear 1000 rows: compiled	N/A	380.9 ms	N/A
🆕	polymorphic-chain update 100/1000 rows × 16: chain	N/A	93.1 ms	N/A
🆕	polymorphic-chain update 100/1000 rows × 16: compiled	N/A	45 ms	N/A
🆕	polymorphic-chain: 200 rows (renderToString): chain	N/A	53.2 ms	N/A
🆕	polymorphic-chain: 200 rows (renderToString): compiled	N/A	5.7 ms	N/A

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 bench/polymorphic-chain (9f465d5) with next (a5d8eae)}