Paint CSS Custom Highlight ranges for Code OSS

[wieslawsoltes]

Active implementation checkpoint — 20 September 2026

Exact upstream heads are WebScene 3cc78ac28101e23f07ded947b44869277da6632d and AppScene acf42662309ea601720ed07c440cf183d7c73fe3; unchanged Code OSS is 645f29cc3176500b4b5762ba887cf2a7f0ffdf2c. Local vscode-demo is 06b5fa4328bae547e40462cbd049b6322f8e8d8e, clean, 294 commits ahead, and intentionally unpushed with Actions disabled.

Focused merge stacks

• Worker/resource stack — merged: WebScene Load dynamically inserted CSS imports asynchronously #702, Complete WorkerOptions and worker load policy #703, Enforce Worker policy across redirect hops #705 and Expose fetch request headers to resource hosts #707; AppScene Expose CSS retained-effect computed values #282; local vscode-demo Add native WebGPU runtime support #10. Dynamic CSS imports, Worker options/credentials/CORS, per-hop redirect validation, and request-header ABI v5 are on main.
• Interactive validation stack — merged: WebScene Present bounded interactive reportValidity feedback #709, Fix validation message text measurement #711, Dismiss stale validation feedback after mutations #712, Bound validation message wrapping and formatting #718, Add bounded validation message formatter ABI #721, Add bounded validation message timeout #723, Bound form ownership invalidation #724, Reflect form labels in semantic validity #725, Implement bounded custom element states #726, Implement live form control collections #727, Implement bounded form state restoration #728 and Wire Flutter validation localization #729; AppScene Wake native runtime for queued WebSocket events #284; local vscode-demo Broaden WebScene compatibility coverage and release gates #11. This includes focused invalid reporting, text-measurement repair, stale-feedback dismissal, bounded wrapping, localization ABI, optional timeout scheduling, and mutation-local form/fieldset ownership invalidation.
• Selector/pseudo stack — merged through scoped selection: WebScene Complete selector matching, specificity, and dependency invalidation coverage #237/Match live hyperlink selector state #730, Implement bounded local-link selector state #735, Implement bounded target-within selector state #736 and Implement functional local-link path depth #737 merged live location selectors; Paint Code OSS placeholder pseudo styles #738 merged paint-only Code OSS ::placeholder; Implement static Code OSS details content #739 merged the bounded static subset for the ten unchanged Code OSS ::details-content rules. Native GitHub stack #745 merged atomically as Implement live Range boundaries for Code OSS highlights #742 (live Range boundaries), Add Highlight and CSS.highlights registry for Code OSS #744 (bounded Highlight/CSS.highlights registry), and Paint CSS Custom Highlight ranges for Code OSS (#746) #747 (functional ::highlight(name) theme cascade plus retained range paint), closing Implement CSS Custom Highlight API for Code OSS ranges #740/Implement live Range boundaries for Code OSS highlights #741/Add Highlight and CSS.highlights registry for Code OSS #743/Paint CSS Custom Highlight ranges for Code OSS #746 at main 7a2d0f8d. PR Paint scoped selection ranges for Code OSS #751 then merged global/scoped ::selection cascade, theme colors, forward/backward range normalization, and retained background/foreground commands at main 2c83b45f, closing Paint scoped ::selection ranges for Code OSS and xterm #750. Focused native/compiler run 35469464706 and precompiled contracts 35469464714 passed. Details animation/compositing, control-part/shadow-selector inventory, and remaining CSS work stay recorded in Complete selector matching, specificity, and dependency invalidation coverage #237/[Epic] CSS features, compatibility, validation, and performance #235.
• Typed transition stack — merged: WebScene PR Implement typed registered custom-property animations #752 merged typed <angle>/<percentage> @property support. PR Implement Code OSS starting-style entry transitions #753 then merged Implement @starting-style entry transitions used by Code OSS #749 at main 3cc78ac2, adding document-level @starting-style, precedence-correct starting cascades, first-render/display re-entry, opacity/2D transform/background-color admission, transition-behavior: allow-discrete, computed-versus-used display behavior, CSSStartingStyleRule, detached-state release, reinsertion, teardown, and a zero-allocation guard across 256 unrelated nodes. Focused precompiled JavaScript 35473084845, Linux native SDK 35473084825, and native Linux document contracts 35473084848 passed.
• Consolidations — open and deliberately unmerged: WebScene Add Code OSS browser and native desktop compatibility #76 is refreshed to ed2eb2c57ec6b1a8bda4bd75747379a7c19c86cf; AppScene Stream native application video directly from file and network URLs #65 is at 2d2407f5e38c4cdd3d851394a5636cc0a8ce9064; vscode-demo Typescript #1 tracks the local unpushed integration branch.

One-agent mode is enforced. No subagent is active. Reusable runtime behavior continues to land in WebScene or AppScene; unchanged Code OSS remains pinned. The change-related #752 and #753 runs passed. Broad PR CI/NuGet plus consolidation, post-merge main and previous-main runs were canceled to release runners; no WebScene job is intentionally retained between focused PRs. Full package, performance, visual, physical-platform and VM qualification remains deferred under the fast implementation directive; focused parser/native correctness and allocation checks are complete locally.

Next: finish the remaining planned CSS and product features, then physical Linux pixels, synchronization/device-loss/resize/soak/performance, visual comparison, VM/computer-use, and unchanged Code OSS Release qualification. Rich clipboard MIME, MULTIPLE/SAVE_TARGETS, recorded desktop-service/cross-platform work, workspace/Explorer, file/save, terminal, Markdown preview, accessibility, lifecycle, package-size, and no-browser promotion gates remain tracked and incomplete.

Parent: #740
Depends on: #741/#743 and PRs #742/#744 in native stack #745
Epic: #235

Scope

Complete unchanged Code OSS Custom Highlight rendering on top of retained Range/registry state:

• parse functional ::highlight(<custom-ident>) selectors and preserve the originating selector/cascade metadata;
• retain only the Code OSS property subset: color and background-color, including custom-property resolution, importance, source order, and stylesheet replacement/removal;
• intersect registered live ranges with text nodes and retained text fragments using UTF-16 boundary offsets;
• emit clipped background rectangles before selected glyphs and foreground text spans with the authored color;
• resolve overlaps by Highlight priority, then registry insertion order; skip collapsed, detached, hidden, display-none, wrong-root, and empty intersections;
• recompute only on registered Highlight/range/style/text/layout changes; static scenes request zero idle frames and add no DOM/visual-tree nodes;
• clean range paint on registry deletion, stylesheet mutation, detach, nested-context teardown, navigation, and engine destruction.

Acceptance

• Unchanged Code OSS chat-find current/other matches and Markdown added/deleted inner ranges paint with authored custom-property colors.
• Same-node and cross-node ranges, wrapping, collapsed ranges, overlap priority/order, hidden/detached text, registry replacement/deletion, stylesheet mutation, and nested contexts have focused scene contracts.
• Work counters scale with intersected registered ranges/fragments and are independent of unrelated DOM, rules, and unregistered Highlights.
• Static highlighted scenes have zero idle frame demand; mutation bursts coalesce; repeated create/delete/navigation return commands, bindings, heap/RSS, and lifecycle counts to baseline.
• The top of native stack #745 carries the focused implementation gate; lower stack CI can be canceled as redundant.

Complete arbitrary highlight pseudo properties, Range mutation adjustment, spelling/grammar/target-text pseudos, and full Selection paint remain separate work.