Qualify the unchanged webview resource broker across representative Code OSS consumers #428

Parent: #266
Webview epic: #264
Release epic: #227

Proven remaining gap

All existing native children of #266 are closed. Merged coverage proves the unchanged VS Code OSS v6 Service Worker for Markdown scripts/styles/images, local-resource admission, 200/206/304/401/404 and HEAD behavior, ranges and validators, bounded streaming, CacheStorage replacement continuity, localhost redirects, parser resources, nested client ancestry, and 100-cycle retirement.

The remaining #266 acceptance item is breadth: the pinned Code OSS tree routes notebook renderer/preload modules, custom-editor assets, extension-detail media, chat/MCP webview modules, Mermaid module/Codicon assets, Simple Browser scripts/styles, and release-note media through the same asWebviewUri authority and v6 worker, but no single executable gate proves that representative matrix without a consumer-specific bypass.

The unchanged v6 worker does not define a host-unavailable offline fallback. Its CacheStorage use retains a validated body for 304 reuse. Existing same-registration active-worker replacement coverage therefore satisfies the product cache behavior; durable cross-engine storage is a separate standards/authority decision and is outside this acceptance-only child.

Focused scope

• Add a bounded executable fixture using the exact pinned 645f29c v6 worker.
• Drive representative script/module, stylesheet/font, image/media, and fetch resources named for Markdown, notebook, custom editor, extension detail, chat/MCP, Mermaid, Simple Browser, and release notes.
• Prove every admitted request reaches the same host broker with the expected path, method, destination, MIME/body behavior, client identity, and no direct host fallback.
• Cover missing and out-of-root denials before bytes, a 32-concurrent-resource batch within the existing 64 MiB queued-body ceiling, one warm validator/cache reuse path, and 100 mixed-consumer cycles with bounded latency, engine-owned memory, process high-water RSS, pending requests, and teardown.
• Run the same contract in Chrome and native, plus exact-head directly related checks.

Ownership and non-overlap

Own only the existing pinned Markdown resource fixture, the Service Worker stream/fetch native gate, a dedicated WebPlatformSubset profile, and focused validation evidence. Runtime files change only if the exact fixture proves a new generic defect.

Do not touch #425/#239 nested CSSOM paths, #288 MessagePort lifetime paths, consolidation #76, AppScene, or vscode-demo.

Acceptance

• Chrome and native pass the representative consumer/resource matrix using the exact pinned v6 worker.
• Security/admission, cache/validator, concurrency/body bounds, and client retirement remain fail-closed and bounded.
• One hundred mixed cycles retain <= 8 MiB V8 heap and external memory; process RSS high-water grows <= 256 MiB. Warm 64 KiB delivery p95 remains <= 100 ms. Current RSS after engine teardown remains diagnostic because system allocators may retain freed transfer pages.
• Directly related hosted checks pass before focused merge.
• Stream and cache admitted Code OSS webview resources #266/[Epic] Qualify unchanged Code OSS webviews and nested document contexts #264/[Epic] Complete remaining Code OSS native release acceptance #227 record exactly what the fixture proves; packaged UI behavior remains with the release/package acceptance owners.