Intercept connected resources through Service Workers

[wieslawsoltes]

Problem

Merged #303/#304 route explicit fetch() through a claimed Service Worker, while dynamically connected script, stylesheet, and image elements still read directly from the host loader. Unchanged webview code can therefore establish a controller but bypass it for resource elements.

Result

• Starts a bounded FetchEvent request before host prefetch for connected script, stylesheet, and image elements, carrying the browser request destination and controlled client generation.
• Keeps the DOM task queue available while the worker resolves or messages its client; completion wakes the runtime instead of blocking the controlled page.
• Uses the worker body for successful handled responses, falls through only when unhandled, and dispatches element error without host fallback for handled rejection, invalid status, timeout, or retired clients.
• Retires pending worker fetch promises when their client generation disappears and preserves the existing 32-request/64 MiB bounds.
• Adds a WPT-derived native/Chromium contract and a 100-cycle native script/style/image, navigation, latency, heap, and RSS gate.

Part of #308 and #266. #308 remains open for parser-blocking initial document resources, nested frame hydration, and CSS url() image interception. #266 retains range/cache-validator, local-resource security, and exact unchanged Markdown product completion.

Validation

• Clean snapshot/native rebuild on rebased exact main b69f931d.
• Portable bootstrap literal regression: 3/3; extracted bootstrap syntax passes packaged Node 24.
• Focused native gate after rebase: 100 script/style/image cycles, p95 0.259 ms; V8 heap 1,183,164 -> 1,183,164 bytes; RSS 38,387,712 -> 49,299,456 bytes; pending-fetch navigation retirement 68.8 ms.
• Native candidate contract: 1/1 document, 3/3 subtests, 87 ms. Evidence: /private/tmp/webscene-308-native-profile-final2-26431500/results.json.
• Google Chrome 153 oracle: 3/3 subtests, 63 ms. Evidence: /private/tmp/webscene-308-chrome-contract-evidence-2.json.
• Existing readable FetchEvent, CacheStorage/TransformStream resource plane, and 100-cycle Service Worker lifecycle gates pass.
• Split IndexedDB bootstrap below the MSVC literal limit #307/Make retained inset parsing portable on macOS #306/Generate effective CSS property metadata #309 paths are disjoint; no Reduce theme-fetch promise continuation latency during workbench startup #297/Keep the IndexedDB bootstrap below the MSVC literal limit #301/Make retained inset length parsing portable below macOS 26 #302/Make retained inset parsing portable on macOS #306 or CSS parser/cascade implementation paths changed.

[wieslawsoltes]

Rebased cleanly onto current main b69f931d after #313. Exact-head native rebuild passed. The focused 100-cycle connected-resource gate passes with p95 0.259 ms, flat V8 heap (1,183,164 bytes), bounded RSS (38,387,712 → 49,299,456 bytes), and pending-fetch navigation retirement in 68.8 ms. The CSS metadata generator suite on the new base independently passes 6/6 plus --check.