Headless Chrome answers pointer and hover media queries from the machine's own input devices

Fact

pointer, any-pointer, hover and any-hover are not emulated by default, so headless Chrome evaluates them against whatever input devices the machine running it has. A laptop with a trackpad matches (any-pointer: fine), and a CI runner with no mouse does not. Emulation.setEmulatedMedia silently ignores these four features: no error, and nothing changes. Touch emulation (Puppeteer's hasTouch: true) does change them, but only towards touch: pointer: coarse, hover: none, no fine pointer.

Why it matters

A page that switches to touch controls when there is no fine pointer is tested in two different modes by the same suite. On the laptop the touch-only controls stay display: none, so a layout test passes there and fails in CI on the first change that moves them. It reads as a CI flake or a font difference between platforms, but the CI result is the one that is true for touch screens.

How to apply

• Set the mode in each test rather than inheriting it from the host: hasTouch: true for touch. No setting forces a fine pointer, so for mouse runs stub the app's own check (for example matchMedia in an init script) or accept that CI will run that test in touch mode.
• Before blaming CI for a layout failure that does not reproduce, run the suite locally in touch mode too.
• Log matchMedia('(any-pointer: fine)').matches in CI once, to know which mode it runs.