Match live form-control pseudo-class state and bounded invalidation

[wieslawsoltes]

Parent epic: #235. Owning workstreams: selector/invalidation #237, cascade/value resolution #238, and dynamic state/frame scheduling #242.

Proven gap

The character-data audit on draft #245 produced a product-neutral textarea candidate that fails before its mutation assertions: :invalid reads the authored value attribute instead of the live control value, and :placeholder-shown is not implemented. That draft deliberately added no competing fix. Existing #237/#238 acceptance names state mutations generally but has no focused form-state source-of-truth and invalidation matrix.

This issue does not own #245's structural child-list routes/checkpoints. Start implementation only after #245 is rebased or its relevant test is relocated without conflict.

Ordered work

1. Inventory form-state pseudos used by current contracts and reachable desktop/webview inputs: :valid/:invalid, :required/:optional, :placeholder-shown, :read-only/:read-write, range states, checked/indeterminate, disabled/enabled, and supported user-valid/user-invalid behavior.
2. Define the live IDL/content-attribute source for input, textarea, select, option, and form state.
3. Add dependency metadata and one bounded invalidation checkpoint for value, selection, placeholder, required, pattern, range, checked, disabled, reset, and form-owner changes.
4. Qualify search, Settings, quick-input, issue-reporter, and extension/webview form surfaces that reach the supported slice.

Acceptance and performance gates

• Chromium/native WPT-derived match and computed-style matrices agree before and after programmatic value writes, native input, attribute mutation, reset, reparenting, and detach/reattach.
• Selector APIs and stylesheet matching use the same state while preserving the specified distinction between live properties and content attributes.
• Initial and mutation scene/pixel checks prove focus, placeholder, validation, and disabled styling without stale retained nodes.
• A 4,096-control matrix records state probes, matched rules, recascade roots/nodes, layout/scene/publication counts, time, allocations, and peak RSS. Unrelated controls/rules do not force full-document work.
• No duplicate structural invalidation implementation is introduced alongside Optimize structural CSS invalidation and DOM mutation checkpoints #245.

Proposed PR stack

1. live form-state model + matcher contracts;
2. dependency invalidation + cascade/scene mutation;
3. remaining pseudo-class slices and WPT promotion;
4. bounded performance and unchanged-product acceptance.

[wieslawsoltes]

Wave 1 scheduling boundary: begin this issue only after capability-matrix PR #271 lands and draft structural PR #245 is reconciled/settled. Consume #271's exact CSS evidence format and preserve #245's ownership of child-list routes, mutation checkpoints, scaling counters, and its current WPT profile edits.

The first #257 stack remains: (1) live input/textarea/select state source plus matcher contracts, (2) state dependency metadata and bounded invalidation/cascade/scene mutation, (3) remaining pseudo-class/WPT slices, and (4) 4,096-control performance plus unchanged-product acceptance. No #245-owned source file should be edited until its merge boundary is known.

[wieslawsoltes]

Taking the first bounded #257 slice from exact WebScene main bea90e8edb14dcb5a4c8e0257117934c3d462ea0.

Live overlap audit: the only open PR is docs-only #76. Prerequisites #245/#271 and the #338/#339 Spotify resize work are merged; this slice will not extend those resize paths or own #238 value-resolution work.

Owned boundary for this slice:

• make :valid, :invalid, and :placeholder-shown consume the existing live input/textarea value state;
• compile the corresponding required/value/placeholder dependencies;
• use one bounded dynamic-state invalidation path for programmatic and native value changes, preserving Optimize structural CSS invalidation and DOM mutation checkpoints #245's structural child-list machinery;
• promote the existing six-case css-textarea-dynamic-state.html contract only with direct Chromium parity;
• add focused selector/computed-style, mutation/lifecycle, scene, 4,096-control cascade/layout timing, heap, and RSS evidence.

Excluded: remaining form pseudos, full constraint validation/pattern/range algorithms, reset/form-owner work, general cascade/value serialization (#238), animation/media scheduling (#242), and further #338/#339 resize optimization. I will re-audit live PR paths before commit and PR.

[wieslawsoltes]

First bounded live form-control state slice merged via PR #342 as 348ea440501c4059da6f95d1fbd6f6159a5df47b (source 0d6d95a8e3007b833cbfa289f413bc70218d2f2d).

Landed behavior:

• :valid / :invalid and :placeholder-shown consume live input/textarea value state;
• programmatic value changes, native edits, content-attribute/default-value synchronization, form reset, detach/reattach, and required/placeholder mutations route through bounded dependency invalidation;
• empty/nonempty transitions avoid unrelated selector work while controls still repaint;
• the existing textarea browser contract is promoted to required.

Evidence:

• Chromium 150: css-textarea-dynamic-state.html 6/6;
• native required profile: 1/1 document, 6/6 subtests;
• focused 4,096-control gate: 1,000 transitions in 7.80331 ms on exact-head Linux CI, stable V8 heap (816,704 -> 816,704 bytes), bounded RSS (92,598,272 -> 97,316,864 bytes);
• exact-head Linux document contracts passed.

The Linux package matrix compiled and executed the new gate, then its broad aggregate failed the same six unrelated tests as the preceding main package run. That baseline comparison is recorded on PR #342.

This issue remains open for the excluded follow-on pseudo-classes and full constraint-validation slices.