[httpsphl]

Why

The owner found the bot's live page blurry when full screen, and slow. Both came from saving resources:

• The page was drawn at 1 pixel per page pixel. On a scaled screen (125%, 150%) or a zoomed app, the picture was stretched.
• Frames were capped at about 15 per second.

What

• Sharp page. browser.resize takes an optional scale: the app's devicePixelRatio × 100. The page is drawn that sharp with deviceScaleFactor, up to 2×. Its size in CSS pixels does not change.
• How the frames are made.
  • The screencast keeps the page's own pixels whatever the scale. I checked this with the real Edge and recorded it in spec 19.
  • So on a sharper screen, the screencast runs at 64 px and only says the page changed. The frame sent to the app is a Page.captureScreenshot (JPEG, quality 60, optimizeForSpeed).
  • The screencast frame is acknowledged only after that screenshot, so screenshots never pile up.
  • The picture kept while the browser rests is sharp too.
• Frame rate. About 30 frames per second while the owner holds the browser, about 15 while they only watch the bot.
• The bot's screenshots (browser_screenshot) stay the size of the page, so they cost the bot the same tokens. They are clipped where the page is scrolled to (Page.getLayoutMetrics → cssVisualViewport.pageX/pageY) and scaled back down (clip.scale).
• Spec 19, 21.3, 21.7 and 21.8 are updated.

Checks

• cargo fmt, clippy -D warnings, cargo test --workspace and pnpm check pass.
• New real-Edge test in browser_panel.rs:
  • at scale 200 the page reports devicePixelRatio 2;
  • its frame is 2000×1400 for a 1000×700 page;
  • the bot's screenshot of a page scrolled to #end is 1000×700.
• I looked at that screenshot once by hand: it showed the black bottom of the test page, so the clip follows the scroll.

Manual check on the real app

1. On a scaled screen, open a bot's browser full screen. The text should be sharp.
2. Take control and scroll. It should feel smoother.
3. Ask the bot for a screenshot. It should still be page-sized.