Unified Frame Pipeline and Low-Performance Paint Tier
Window, VisualViewport, and key scroll measurements now share one read-then-write frame pipeline, with a clear solid-surface tier for Save-Data and confirmed low-end devices.
# Unified Frame Pipeline and Low-Performance Paint Tier
This release consolidates scattered window, VisualViewport, and key scroll work into one auditable frame scheduler, while giving data-saving and confirmed low-end devices a paint fallback that preserves function and contrast.
## Read once, then write once per frame
- `mobile-shell.js` is now the only native listener for window resize plus VisualViewport resize and scroll. Repeated requests for the same key within an event storm keep the latest job, all layout reads run first, and all style writes follow in the same frame.
- The Home wallpaper stage and desktop-icon geometry, Knowledge reading progress and table of contents, mobile Dock, motion layer, and focused Quick Transfer control use the same pipeline. Route exits unsubscribe their related jobs.
- Viewport dimensions, keyboard offset, and the Dock selection surface commit together. When native page scale differs from 1, the smaller VisualViewport is not misclassified as an on-screen keyboard.
- Build guards reject a second native viewport listener in public scripts and verify that primary consumers retain the keyed measure/mutate contract.
## A clear low-performance paint tier
- `low` activates when Save-Data is enabled or the browser explicitly reports no more than 2 logical cores or 2 GiB of device memory. Devices with unknown capability remain `normal` instead of receiving a guessed downgrade.
- The low tier removes large blur, backdrop filters, wallpaper filters, looping clouds, permanent `will-change`, and full-page View Transitions. Solid high-contrast fallbacks cover the top bar, taskbar, Dock, account layer, and modal backdrop.
- The normal tier keeps the XP, Pixel Art, and Y2K wallpaper, glass depth, and interactions unchanged. Small icon shadows and short transform/opacity feedback remain available.
## Verification boundary
Controlled Headless Chrome passes 117 checks: 40 same-frame event groups produce one read and one write phase; 390×844 and 844×390 viewport variables match final Dock geometry; native 2× page scale yields zero keyboard offset; Save-Data, two-core, and unknown-capability profiles select the correct tier; and the low-tier screenshot retains clear text and controls without large paint effects. This automation does not emulate or claim validation of a real iOS or Android on-screen keyboard. No production data, release, or deployment is involved.
