Add a focused native webview removal regression check

[reowens]

The desktop preload verifier runs in a VM and cannot observe Electron's native guest removal callback. A private standalone fixture found 4 WebViewElement.disconnectedCallback exceptions on 44.4.2 after all guests had reached bridge, DOM, picker and attachment readiness. A same-input 44.5.1 run had 0 exceptions. Current upstream has already upgraded to44.4.5 in PR16961; an additional current-source check on official44.4.5 also passes all 4 cases.

Proposed scope: add 1 opt-in desktop verification command and 1 self-contained native fixture script. Keep the current runtime and lockfile. Load only the built host/picker preloads, require readiness and attached identity, then remove guests under both context-isolation settings with and without an explicit host DOM-ready barrier. Capture host exceptions/error console, step deadlines, creator-collected exit and captured-process cleanup. Use fresh private data with navigation/permissions denied, without importing the desktop main or starting the server.

This is separate from open PR13265, which fixes the macOS VM environment. It does not implement tab ordering from PR13799, reproduce the historical sandbox startup failure, or add an application runtime fix.

A 2-file patch and local receipts are prepared against b1ec4b36876e7f3ad03a1e9e921286ec7d58fe95. Current-source 44.4.5 validation exits0 with all 4 cases ready,0 host exceptions/error console, no timeout and all 8 captured PIDs absent. Preloads were built with reused matching dependencies and direct Rolldown 1.2.5, not the upstream Vite+ 1.0.0 pipeline. Only macOS arm64 was tested, and removals are already attached. Native stderr is retained, including Widget/SharedImageManager messages. Public evidence must accompany any submission.

Would you accept this native regression-check scope as an outside maintenance contribution, or prefer the fixture retained as reproduction evidence only?

Prepared with GPT-6.1-Sol through the Codex harness in T3 Code, using1 agent and primary-agent review.