Let local desktop tabs opt into the server browser

[carlos-443-diaz]

Problem

When the macOS desktop app owns a local Browser tab, remote clients receive its preview stream. After macOS locks the screen, Electron webviews can stop painting, leaving remote viewers connected to stale or blank frames. Keeping the desktop app running is desirable because it remains the normal local client.

Existing capability

T3 already supports server-browser tabs, sticky headless preview sessions, and streaming those tabs to desktop, web, and mobile clients. Remote environments can already move tabs between desktop and server browser hosts.

Proposed scope

Add an explicit per-tab action for the primary local environment: Open in this environment server browser. It would mark that preview session as headless and move only the selected tab to the existing server-browser path. Defaults would not change, and normal desktop tabs would retain desktop profiles, passkeys, and native tooling.

Why explicit selection

Automatic lock-time migration would reopen state in another browser process and could lose profile, login, or page state. Per-tab selection makes that tradeoff visible and predictable.

Verification completed

A focused implementation passed the changed-package checks and browser tests. In a controlled macOS test, a paired tablet kept control of the selected tab, loaded a page, scrolled it, and reloaded it while the Mac was locked. The production signed Nightly was not replaced.

Would maintainers accept this focused extension of the existing server-browser workflow?