# Browser Capture Harness

The desktop capture harness is the real-Electron verification path for browser screenshots.
It validates the compositor behavior that unit tests cannot see:

- the resident automation `<webview>` starts in the production parking state;
- the parked guest has no copyable viewport frame;
- the resident webview guest is sized to 1280x800 logical pixels;
- the app-style prep sequence moves the host to a paintable 1x1 clipped state, waits two animation frames and a layout read, then both viewport `capturePage` and full-page CDP screenshots return real pixels;
- restore returns the host to offscreen parking after every capture.

Run it with the repo Electron:

```bash
npm run capture-harness --workspace=@getpaseo/desktop
```

The harness writes PNG evidence and `results.json` to:

```text
packages/desktop/capture-harness/out/
```

A passing run prints `PASS` lines for guest sizing, the expected parked-capture failure,
five viewport prep captures, five full-page prep captures, and final completion. The PNG
sizes may be device-pixel scaled; on a Retina display the 1280x800 logical viewport is
usually saved as 2560x1600.

## Mechanism

Electron captures copy from the guest web contents' compositor surface. A resident
webview parked at `left:-20000px` and `opacity:0` does not have a copyable surface, and
`capturePage({ stayHidden:false })` or CDP `Page.captureScreenshot` cannot rescue it.

Before pixel capture, the app renderer temporarily makes the resident host paintable:
`left:0`, `top:0`, `opacity:1`, `pointer-events:none`, host size `1x1`, and
`overflow:hidden`, with the full-size 1280x800 webview inside. Main captures only after
the renderer acknowledges two animation frames plus a `getBoundingClientRect()` read, and
the renderer restores parking in a `finally`.