Puppeteer's setViewport reloads the page whenever isMobile or hasTouch changes

Fact

page.setViewport() compares isMobile and hasTouch with the page's current emulation and, if either differs, ends by calling page.reload(). The documentation only says this happens "in certain cases". Changing just width, height or deviceScaleFactor never reloads.

Why it matters

• Switching a page into or out of phone emulation mid-test throws away everything the app held in memory: a game in progress, an open dialog, a filled form. The page is back at its start screen and nothing reports it.
• Before the first goto the reload re-creates about:blank, and scripts registered with evaluateOnNewDocument run there. That document has an opaque origin, so touching localStorage throws SecurityError: ... Access is denied for this document, which arrives as a pageerror and fails any "no page errors" assertion.

How to apply

• Pick isMobile and hasTouch once per page, before navigating, then sweep screen sizes with setViewport({ width, height }) and those two unchanged.
• Size media queries (width, height, aspect-ratio) need no mobile emulation at all; only pointer/hover queries and meta-viewport layout do.
• Guard init scripts that use storage: wrap them in try { … } catch {}, or return early when location.protocol === 'about:'.